Sérgio Ferreira-Cardoso

Morphological convergence and dental simplification in myrmecophagous placentals

Introduction

In biology, convergence is a phenomenon characterized by the evolution of similar features without direct common ancestry. Similar selective pressures may result in identical phenotypes evolving independently in two or more lineages. Once seen as exceptional, convergent evolution is today considered as pervasive (McGhee, 2011). In part, cases of convergence can be explained by how organisms develop under the laws of physics, how they originate from a single cell, and how their organization is coded and transmitted to the next generation (developmental constraints). On the other hand, some phenotypes are functional in nature, while others constitute lethal conditions that cannot survive (functional constraints; McGhee, 2001[START_REF] Mcghee | The geometry of evolution: adaptive landscapes and theoretical morphospaces[END_REF]. Life is therefore limited to the intersection of developmentally and functionally viable forms [START_REF] Mcghee | Theoretical morphology: the concept and its applications[END_REF], limiting phenotypic variation and leading to similar responses under convergent selective pressures providing evolutionary replicates [START_REF] Losos | Improbable destinies: fate, chance, and the future of evolution[END_REF].

Among countless examples of evolutionary convergence, one of the most striking is that of antand termite-eating placental mammals (Redford, 1987). The ecological convergence towards dietary specialization was accompanied by numerous adaptations at the morphological, physiological, behavioral, and genetic levels [START_REF]Quick-snacking anteater avoids attack[END_REF]Redford & Dorea, 1984;McNab, 1985;[START_REF] Rose | [END_REF][START_REF] Delsuc | Convergence of gut microbiomes in myrmecophagous mammals[END_REF][START_REF] Emerling | Enamel loss in placental mammals[END_REF]. Extant strict myrmecophagous placentals eating more than 90% of termites and/or ants include five lineages: anteaters, the giant armadillo, pangolins, the aardwolf, and the aardvark (Fig. 1; Redford, 1987). Most of these species, historically classified as Edentata (except the aardwolf; see 'Phylogenetic background'), show numerous convergently evolved morphological characters, such as tooth reduction/loss, elongated snouts, vermiform sticky tongues, and strong claws and forelimbs for digging into social insect nests [START_REF] Rose | [END_REF]Davit-Béal et al., 2009;[START_REF] Casali | Morphology of the tongue of Vermilingua (Xenarthra: Pilosa) and evolutionary considerations[END_REF]Goździewska-Harłajczuk et al., 2018;Ferreira-Cardoso et al., 2019).

Cranial traits constitute the most defining characteristics of myrmecophagous placentals [START_REF] Gaudin | Reexamination of the morphological evidence for the cohort Epitheria (Mammalia, Eutheria)[END_REF]Gaudin & Branham, 1998;Reiss, 2001). This is mostly due to the plasticity of the mammalian feeding apparatus and to its role in the several adaptive radiations of the group (Hiiemae, 2000;Schwenk, 2000). This adaptive evolution of the placental skull, combined with conserved developmental processes, resulted in a compartmentalization of the skull in small adaptive units, or modules (Olson & Miller, 1958;Cheverud, 1982a;Goswami, 2006;Porto et al., 2009). These developmental modules often translate into sets of highly correlated traits (phenotypic modules), with a main functional role, an underlying genetic and developmental basis, and a fair degree of independence within an organism [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]Wagner, 1996;Klingenberg, 2005). Under a certain adaptive landscape (e.g., dietary specialization), variational properties such as trait correlation and modularity were suggested to increase the amount of change in the direction of selection (evolvability; Riedl, 1978;Hansen & Houle, 2008;[START_REF] Marroig | The evolution of modularity in the mammalian skull II: evolutionary consequences[END_REF]. The unique cranial phenotype associated to myrmecophagy is, therefore, an example of the trade-off between facilitation and constraint of morphological variation in the context of a functionally and physiologically demanding dietary regime. (Kumar et al., 2017). Divergence times (branch lengths) were adjusted for pangolins (Gaubert et al., 2018), xenarthrans (Gibb et al., 2016), and afrotherians (Meredith et al., 2011). Branches colored in red indicate myrmecophagous species; the branch colored in yellow indicates a non-obligate myrmecophagous species; tip labels in blue indicate clades previously historically ascribed to the Edentata.

Ant-and termite-eating placentals have sparked the interest of several studies for more than a century, mainly related to their tooth development (Gervais, 1867;Rose, 1892;[START_REF] Röse | Uber rudinmentare Zahnanlagen der Gattung Manis[END_REF]Martin, 1916;Anthony, 1934a;Davit-Béal et al., 2009), and their loss of chewing abilities and evolution of modified masticatory and hyoid apparatus (Owen, 1856;Reiss, 1997;Endo et al., 1998Endo et al., , 2007Endo et al., , 2017;;Naples, 1999a). Despite all the drawn attention, the use of modern geometric morphometric methods is yet to be undertaken on the skull of myrmecophagous placentals, while it could enable to assess the phenotypic variation patterns (e.g., Cheverud, 1982[START_REF] Cheverud | Morphological integration in the saddle-back tamarin (Saguinus fuscicollis) cranium[END_REF]Hallgrímsson et al., 2004;[START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF].

Such methods can also provide new insights into ontogenetic patterns (Cheverud, 1982b;Klingenberg, 2016) and systematics [START_REF] Palci | Geometric morphometrics, homology and cladistics: review and recommendations[END_REF]. Additionally, the advent of X-ray µ-computed tomography (µCT) and enhanced-contrast scanning protocols now allows performing non-destructive analyses to explore osteological and soft-tissue traits at an unprecedented scale and precision.

The feeding apparatus of myrmecophagous placentals provides a particularly interesting framework to study morphological convergence associated with ecological adaptations. The developmental processes involved in skull formation are well-documented and modular parcellation and its relationship to functional constraints is established for several model and non-model placental species.

Moreover, part of these developmental processes, such as face/rostrum elongation, tooth development, or bone-muscle interaction, underlies most of the convergent phenotypic traits associated to myrmecophagy.

The myrmecophagous skull thus offers a case study of morphological convergence.

Methodological framework

A set of different methods was used in order to perform the four studies presented in the different chapters of this thesis. A detailed 'Materials and methods' section is provided for each chapter and, therefore, I here provide only the broad outline of my methodological approach.

Data acquisition

First, and foremost, I visited five of the largest natural history collections in the World, including the Natural History Museum (London), the Musée Royal de l'Afrique Centrale / Koninklijk Museum voor Midden-Afrika (Africa Museum; Tervuren), the Museum für Naturkunde (Berlin), the American Museum of Natural History (New York), and the National Museum of Natural History (Washington, DC).

Additionally, I borrowed osteological and wet specimens from the Muséum National d'Histoire Naturelle (Paris), and the Museum of Vertebrate Zoology (Berkeley). Each visit consisted in between one and two days of comparative anatomy work, followed by the placement of three-dimensional (3D) homologous anatomical landmarks (types I and II; Fig. 2). This last step was performed with a Revware MicroScribe M digitizer (accuracy: 0.0508 mm). The number of landmarks placed varied between 85 and 119, according to the clade considered. In total, I landmarked 703 specimens belonging to myrmecophagous species, and some non-myrmecophagous outgroups, including sloths, armadillos, hyenas, bears, and foxes. All resulting data was subsequently processed using Avizo (FEI), Fiji (Schindelin et al., 2012), and MorphoDig [START_REF] Lebrun | MorphoDig[END_REF]. These softwares were used to compress the data and generate threedimensional surfaces (e.g., [START_REF] Ferreira-Cardoso | Floccular fossa size is not a reliable proxy of ecology and behaviour in vertebrates[END_REF][START_REF] Martinez | Convergent evolution of an extreme dietary specialisation, the olfactory system of worm-eating rodents[END_REF].

Lastly, I dissected the heads of six specimens of anteaters stored at the Institut de Sciences de l'Evolution (Montpellier) and at the Institut Pasteur de Guyane (Cayenne). These specimens were dissected at Montpellier and Cayenne, and were subsequently stained with iodine in order to increase the contrast of head muscles and allow to µ-CT scan and digitally reconstruct their morphologies. Some of these specimens were subjected to serial slicing in order to produce histological sections of muscles and mandibles. Histological procedures were performed at the Institut de Recherche en Cancérologie de Montpellier (IRCM).

Data analysis

All morphometric data were processed and analyzed using free statistical analyses software R (Team, 2013). Geometric morphometrics analytical procedures were implemented with the geomorph v.3.5.0 R package (Adams et al., 2017) and the R code provided in Claude (2008). Most analyses implied the Procrustes superimposition (Rohlf & Slice, 1999) of the landmark data sets in order to scale them to centroid size and optimally translate and rotate the specimens using least-squares criterion. Specific R packages and functions are listed in each chapter.

Phylogenetic framework Historical review

In 1742, the French doctor and naturalist Félix Vicq-d'Azyr published the second volume of his "Système anatomique: quadrupèdes" (Vicq-d'Azyr, 1742), as part of a book series named "Encyclopédie Méthodologique". In this book, Vicq-d'Azyr named a new clade of mammals that he designated as "édentés/Edentati". The diagnostic trait for this group was the lack of incisor teeth. It comprised four genera, including sloths (Pigri), armadillos (Loricati), anteaters and the aardvark (Myrmecophagi), and pangolins (Squammei) [START_REF] Vicq-D'azyr | Systême anatomique des quadrupèdes[END_REF]. The name Edentata was posteriorly adopted by naturalists, and its structure re-organized into five different groups: armadillos, anteaters, sloths, aardvarks, and pangolins (e.g., [START_REF] Cuvier | Tableau élémentaire de l'histoire naturelle des animaux[END_REF]. Edentata has been used to designate these taxa (Rose, 1892;Tims, 1908), on the basis of common morphological traits that were considered as synapomorphies of the group. [START_REF] Huxley | A manual of the anatomy of vertebrated animals[END_REF] diagnosis of the Edentata (or Bruta, which translates to brute, coarse, or beast) reflected some of the convergently evolved morphological traits related to myrmecophagy. These include tooth loss or reduction, tooth structure simplification, hypselodonty, monophyodonty (except in some armadillos) and forelimbs adapted for digging [START_REF] Huxley | A manual of the anatomy of vertebrated animals[END_REF]. [START_REF] Huxley | A manual of the anatomy of vertebrated animals[END_REF] divided the Edentata into two groups based on their feeding on plants (sloths; Phytophaga) or insects (Entomophaga), the latter group including anteaters, pangolins, armadillos, and aardvarks. Each of these taxa were placed separately in their own taxa, but no tentative affinities were proposed. By the time Huxley published his work, a little more than a hundred years after the formalization of the Edentata, an increasingly amount of knowledge on the anatomy and physiology of these mammals allowed researchers to question the pertinence of such a grouping. [START_REF] Huxley | A manual of the anatomy of vertebrated animals[END_REF] himself precedes his diagnose and description of the Edentata by stating the group was "ill-defined" and heterogeneous.

However, it would take until the early 1900's for the first formal division of the Edentata in three clearly different orders. Weber (1904, p. 412) argued that although it became usual to group these taxa in the same order, the morphological differences were too many for the classification to be coherent. In the same sequence, Weber referred to the reduced dentition and tooth structure simplification as a "multiple reduction and transformation" (translated from German) that could not be used as a grouping factor (see below). [START_REF] Weber | Die Säugetiere. Einführung in die Anatomie und Systematik der recenten und fossilen Mammalia[END_REF] considered the Edentata as an "inferior" group within the therian mammals, the Paratheria, leaving its relationships with the remaining mammals ill-described. [START_REF] Weber | Die Säugetiere. Einführung in die Anatomie und Systematik der recenten und fossilen Mammalia[END_REF] divided the edentates in two groups: i) the Nomarthra including two orders of species with normal vertebral articulation (pangolins and aardvarks); ii) the order Xenarthra showing abnormal accessory articulations in the last thoracic and lumbar vertebrae (anteaters, sloths, and armadillos). Additionally, [START_REF] Weber | Die Säugetiere. Einführung in die Anatomie und Systematik der recenten und fossilen Mammalia[END_REF] coined the term Pholidota, the order in which pangolins are still classified, thus replacing the previous Squamata designation that was in synonymy with the reptile clade. Within Xenarthra, he maintained the previously used divisions between anteaters (Myrmecophagidae), sloths (Bradypodidae), and armadillos (Dasypodidae).

Since the early 20 th century, the name Edentata has been used to refer to Xenarthra, and the similarities between the latter with Pholidota and Tubulidentata have been attributed to convergent evolution toward myrmecophagy (e.g., [START_REF] Rose | [END_REF]McGhee, 2011). This classification became broadly accepted, even before the beginning of the molecular phylogenetic era, with Xenarthra being considered on its own separate clade within Eutheria, split into two orders Cingulata (armadillos) and Pilosa (sloths and anteaters) [START_REF] Mckenna | Toward a phylogenetic classification of the Mammalia[END_REF]. [START_REF] Mckenna | Toward a phylogenetic classification of the Mammalia[END_REF] considered the Pholidota on their own incertae sedis clade, while the Tubulidentata were grouped with the ungulates with a similar rank to the artiodactyl, proboscidean, or sirenian orders. These proposals, however, were not corroborated by the more recent molecular phylogenetic analyses (see below).

Present state of the phylogeny of placental mammals

Since the 1980's-1990's onwards, molecular phylogenies provided increasing evidence confirming the polyphyly of the Edentata (De [START_REF] Jong | Protein sequence analysis applied to xenarthran and pholidote phylogeny. The evolution and ecology of armadillos, sloths and vermilinguas[END_REF][START_REF] Springer | Endemic African mammals shake the phylogenetic tree[END_REF][START_REF] De Jong | Molecules remodel the mammalian tree[END_REF]Murphy et al., 2001b). Pangolins are a sister group to carnivores and are nested within the Laurasiatheria [START_REF] Sarich | Mammalian systematics: twenty-five years among their albumins and transferrins[END_REF]Murphy et al., 2001b,a;Meredith et al., 2011). Aardvarks form a sub-clade with tenrecs and elephant shrews, within the Afrotheria [START_REF] Waddell | Towards Resolving the Interordinal Relationships of Placental Mammals[END_REF][START_REF] Asher | The new framework for understanding placental mammal evolution[END_REF]Meredith et al., 2011). Xenarthrans are the group with the most undefined position in the placental tree [START_REF] Nishihara | Retroposon analysis and recent geological data suggest nearsimultaneous divergence of the three superorders of mammals[END_REF][START_REF] Teeling | Making the impossible possible: rooting the tree of placental mammals[END_REF][START_REF] Foley | Mammal madness: is the mammal tree of life not yet resolved?[END_REF], with its relationships changing in each of the three proposed hypothesis: i) Atlantogenata-Boreoeutheria (Fig. 1); ii) Afrotheria-Exafroplacentalia; iii) Xenarthra-Epitheria.. To date, the root of the placental tree is still unresolved, with all three hypotheses being currently considered equally likely [START_REF] Nishihara | Retroposon analysis and recent geological data suggest nearsimultaneous divergence of the three superorders of mammals[END_REF][START_REF] Teeling | Making the impossible possible: rooting the tree of placental mammals[END_REF]. Nevertheless, all provide unequivocal evidence for the polyphyly of Cuvier's Edentata, asserting the high degree of morphological convergence resulting from directional selection towards a myrmecophagous dietary regime.

Dissertation's main goals

In this thesis, I combined comparative anatomy and geometric morphometrics of the myrmecophagous skull and mandible, using modern µCT techniques and large museum collection sampling in order to provide new insights into the convergent evolution of the head, skull, and muscles of ant-and termite eating placental mammals. The studies here presented focus on the skull of 15 myrmecophagous placental species, including anteaters, the giant armadillo, pangolins, the aardvarks, and the aardwolf, as well as their closely related species.

In the first chapter, I used a landmark-based approach to describe and quantify inter-and intraspecific skull shape variation, as well as allometric patterns of the World most heavily poached mammals, pangolins (Pholidota).

In the second chapter, I analyzed the internal anatomy of the mandible of all myrmecophagous placental clades and compare it to non-myrmecophagous taxa in order to re-interpret phenotypic convergence and discuss functional aspects of tooth regression. I additionally used collection specimens and contrast-enhanced µCT scanning to perform a comparative anatomical description of the masticatory, hyoid, lingual, and facial musculatures of the three anteater genera (Vermilingua).

Finally, I assessed and compared intra-and interspecific phenotypic covariation patterns between myrmecophagous placentals, using a geometric morphometric approach. I used exploratory and confirmatory methods to understand the impact of myrmecophagy-driven morphological adaptation in skull modularity and integration.

The main goal of this dissertation was to generate knowledge on the cranial morphological convergence based on comparative anatomy and geometric morphometrics approaches, and to contribute to an integrative project (ConvergeAnt) including other aspects of myrmecophagy-driven adaptation at the genomic and microbiome levels.

Chapter 1: Morphological evolution, classifications and phylogeny From early in the history of humankind, the description of biological diversity led naturalists to create divisions as a mean to classify life in a logical way. The formal classification of living beings have their roots in the works of Aristotle, Theophrastus, or Pliny the Elder [START_REF] Lecointre | The tree of life : a phylogenetic classification[END_REF]. Since Greco-Roman times, several classification methods were proposed in order to create a widespread and "correct" way to group biological entities. In 1758, Carl Linnaeus published the tenth edition of his most remarkable work, Systema Naturae, in which a hierarchical system based on morphological similarities was proposed. It is in this edition that Linnaeus generalized the use of a binomial nomenclature for species.

This classification was based on the idea of a natural order dictated by in the act of the creation of life by God [START_REF] Linnaeus | Systema naturae[END_REF]. As the philosophers of Ancient Greece, 18 th century naturalists thought that the identity and function of biological entities determined their classification (essentialism; [START_REF] Cartwright | Some remarks on essentialism[END_REF][START_REF] Lecointre | The tree of life : a phylogenetic classification[END_REF]. The notion of time and the concept of phylogenetic relationships, as we know them today, were not present in Linnaeus' work. Nevertheless, this classification is the foundation of the taxonomic system has been used to the present day.

The Linnean classification scheme proved useful in the classification of living beings, but the French Revolution, at the end of the 18 th century, led to a change in how naturalists conceived nature. Despite many philosophers had expressed proto-transformist ideas since Ancient Greece, it was the accumulation of knowledge during the Enlightenment and the separation of the religious and intellectual realms during the transition of the 18 th and 19 th centuries that propelled the ideas that species were not immutable entities [START_REF] Stott | Darwin's ghosts: the secret history of evolution[END_REF]. De Maillet, Erasmus Darwin, or Lamarck are just some examples of the people who paved the way to Charles Darwin and Alfred R. Wallace [START_REF] Stott | Darwin's ghosts: the secret history of evolution[END_REF]. If the dogma of a natural hierarchy determined by God lost consensus within the scientific community, it took until 1859 for the formalization of a hypothesis that could explain the diversity of groups (or taxa) described. Charles Darwin's On the Origin of Species (1859) is the keystone of evolutionary biology, associating facts from different research fields such as paleontology, geology, and economics to propose a hypothesis that could explain the origin of biodiversity. But the most revolutionary aspect of this work was the interpretation of species as stages, in time and space, of a variation spectrum. The main reason for this, was the fact that Darwin shifted the scale of morphological description and comparison. While previous thinkers followed a typical essentialist approach to classify living beings, Darwin defined species based on simple mathematical concepts such as average and variance (Lecointre and Le Guyader, 2001). Based on his observations and published works on agricultural plant varieties and livestock breeding, Darwin became aware of the potential for variation within a single species [START_REF]On the origin of species by means of natural selection or the preservation of favoured races in the struggle for life[END_REF]. As such, the boundaries of previously created "boxes" in which taxa were organized became less clear. Darwin's main question went beyond the simple attribution of living entities to a species, aiming at understanding why species were relatively discrete entities (average) while exhibiting an enormous potential to vary (variance; Lecointre and Le Guyader, 2001). Since then, the classification of living beings evolved into a two-layered universe, in which the first layer consists of an observed pattern, and the deeper layer of the processes underlying such pattern. With Darwin, variation became a central focus in biology and naturalist work shifted from recognizing morphological patterns to understanding why a certain species is constrained to present a specific set of average traits. Furthermore, given that life can be interpreted as a variation continuum, new research fields focused on the causes of variation and the constraints limiting it.

In sum, Darwin's main conclusion was that all living and fossil species are related, to some degree, and that the sets of traits that characterize species (phenotypes) are, in part, the result of selective pressures acting during a number of generations. The potential variation range presented by a species is thus reduced and the observed patterns are the result of both genealogical (phylogenetic) and environmental constraints. [START_REF]On the origin of species by means of natural selection or the preservation of favoured races in the struggle for life[END_REF] was the first to introduce the principle of genealogy -hierarchical relationship between individuals of the same kin -to the interpretation of life. From 1859 onwards, the concept of phylogenetic tree would be used as a means to associate phenotypic resemblance with the idea of ancestry (time dimension). The view of descent with modification is behind the foundation of evolutionary biology as a research field, and the source for systematics, the study of the relationships between living and extinct taxa (Lecointre and Le Guyader, 2001). Although Darwin's book became the paramount work in evolutionary biology, Alfred Wallace also proposed evolutionary hypotheses. As a result, both signed the first document to ever propose natural selection as the mechanism behind speciation (Darwin and Wallace, 1958). Despite the importance of Darwin and Wallace's works, most keystone concepts in evolutionary biology were defined either before, or after their publication. The best example is probably the word phylogeny, which was not coined until 1866, when Ernst Haeckel tried to synthesize Lamarck's and Darwin-Wallace's hypothesis in his "Ontogeny recapitulates phylogeny" (or biogenetic fundamental law; [START_REF] Haeckel | Generelle Morphologie der Organismen[END_REF]. While the idea that the embryonic stages of "higher" species represented the adult stages of "primitive" organisms has been refuted several times (e.g., [START_REF] Sánchez-Villagra | Embryos in deep time: the rock record of biological development[END_REF], Haeckel produced the first figure with a non-schematic phylogenetic tree, in which the main groups of animals, plants, and the paraphyletic unicellular eukaryotes (Protista) are represented. Although Haeckel's biogenetic fundamental law and tree topology were not confirmed by posterior scientific and technological developments, his tree is a landmark that preconized the future of biology. The interpretation of the trait variation in a phylogenetic context is today one of the richest fields in the life sciences.

From the late 1800's to the 1960's, the description and quantification of phenotypic variation constituted the main source of information used to deduce phylogenetic relationships [START_REF] Mooi | Phylogenies without synapomorphies-a crisis in fish systematics: time to show some character[END_REF][START_REF] Lee | Morphological phylogenetics in the genomic age[END_REF]. Recently, molecular data became increasingly used to perform phylogenetic inference, as continual methodological developments and computational capacity allow to treat an increasing amount of data (genome scale) and generate well-supported, fully-resolved trees [START_REF] Lee | Morphological phylogenetics in the genomic age[END_REF]. Molecular phylogenetics has allowed new insights into the tree of life and an increasingly better understanding of the evolutionary history of living beings [START_REF] Zuckerkandl | Molecules as documents of evolutionary history[END_REF][START_REF] Woese | Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya[END_REF]. The development of these techniques has even allowed scientists to perform phylogenetic inference based on DNA and proteins collected from fossil specimens [START_REF] Yang | Phylogenetic resolution within the Elephantidae using fossil DNA sequence from the American mastodon (Mammut americanum) as an outgroup[END_REF][START_REF] Poinar | Molecular coproscopy: dung and diet of the extinct ground sloth Nothrotheriops shastensis[END_REF][START_REF] Delsuc | Ancient mitogenomes reveal the evolutionary history and biogeography of sloths[END_REF][START_REF] Presslee | Palaeoproteomics resolves sloth relationships[END_REF]. In some cases, the coupling of fossil-based molecular and morphological data has completely restructured the morphology-based phylogenetic relationships, as recently exemplified by the case of sloths [START_REF] Delsuc | Ancient mitogenomes reveal the evolutionary history and biogeography of sloths[END_REF], or resolved the phylogeny and biogeography of emblematic species like the New Zealand moas [START_REF] Cooper | Complete mitochondrial genome sequences of two extinct moas clarify ratite evolution[END_REF][START_REF] Haddrath | Complete mitochondrial DNA geonome sequences of extinct birds: ratite phylogenetics and the vicariance biogeography hypothesis[END_REF]. Molecular phylogenies are, therefore, invaluable tools to propose alternative scenarios for the evolutionary history of phenotypic traits, facilitating the interpretation of ontogenetic, functional, and ecological signals by establishing a solid basis for ancestral state estimation [START_REF] Lee | Morphological phylogenetics in the genomic age[END_REF]. On the other hand, the study of evolution in a deep time context will always remain dependent on morphological data (fossils). Fossils are the only way by which the accurate estimation resulting from modeling of macroevolutionary dynamics (e.g., extinction rates) can be obtained [START_REF] Rabosky | Extinction rates should not be estimated from molecular phylogenies[END_REF]. As such, the very basis of the study of evolution, as well as the reliability of its interpretation, still relies on concepts arising from comparative anatomy studies. The most relevant of all these concepts is almost certainly that of homology/homoplasy, which has become the conundrum of morphology-based phylogenetic analyses and is, at the same time, the engine boosting the field of comparative anatomy.

1.2-Speciation and species delimitation

Until this point, I focused this section on the aspects that gravitate around the taxonomic unit, more specifically the species. In its most classical concept, a species can be discerned by phenotypic distinctiveness [START_REF] Benton | Speciation in the fossil record[END_REF]. This morphological species concept was adopted by [START_REF]On the origin of species by means of natural selection or the preservation of favoured races in the struggle for life[END_REF] in order to articulate his hypothesis of the speciation process. In focusing on morphological variation and polymorphism, Darwin and Wallace [START_REF] Darwin | On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection[END_REF] provided the first glimpse of the mechanisms behind it. Phenotypic variation arises by the mutation of the genome, and genetic assimilation of such variation [START_REF] Waddington | Canalization of development and the inheritance of acquired characters[END_REF](Waddington, , 1953) ) plays a key role in speciation [START_REF] Benton | Speciation in the fossil record[END_REF]. However, how can a species be defined if it displays extreme phenotypic variation (i.e., polymorphism; [START_REF] Mallet | A species definition for the modern synthesis[END_REF] or almost no variation at all (i.e., cryptic species; [START_REF] Bickford | Cryptic species as a window on diversity and conservation[END_REF]?

The biological concept of species proposed the possibility of interbreeding as a solid criterion to identify a species [START_REF] Dobzhansky | Genetics and the Origin of Species[END_REF][START_REF] Mayr | Systematics and the Origin of Species[END_REF]. This concept has limitations exemplified by the natural occurrence of fertile hybrids of different species of palm trees [START_REF] Papadopulos | Ecological speciation in sympatric palms: 4. Demographic analyses support speciation of Howea in the face of high gene flow[END_REF] or the hybridization of putatively distinct duck species in captivity [START_REF] Mallet | A species definition for the modern synthesis[END_REF]. Speciation is a complex process, involving multiple mechanisms such as natural selection (including sexual selection), genetic drift, or mutation. Given this complexity, other concepts of species were since then proposed and discussed [START_REF] Mayden | A hierarchy of species concepts: the denouement in the saga of the species problem[END_REF][START_REF] Queiroz | The general lineage concept of species, species criteria, and the process of speciation[END_REF], 2007). Speciation is today considered as isolation in one or several ways, may it be due to extrinsic (e.g., behavior, ecology;[START_REF] Stresemann | Oekologische Sippen-, Rassen-und Artunterschiede bei Vögeln[END_REF][START_REF] Thorpe | The evolutionary significance of habitat selection[END_REF] or intrinsic (e.g., egg-sperm incompatibility, low hybrid fitness) factors [START_REF] Ptacek | The pattern and process of speciation[END_REF]. As a result, species delimitation is increasingly based on an integrative approach, including the assessment of morphological distinctiveness and gene flow interruption/reduction [START_REF] Puillandre | An integrative approach to species delimitation in Benthomangelia (Mollusca: Conoidea)[END_REF].

The relationship between genetic and morphological differentiation is today frequently tested (Barlow, Jones, & Barratt, 1997;[START_REF] Amato | Morphology, phylogeny, and sexual cycle of Pseudo-nitzschia mannii sp. nov. (Bacillariophyceae): a pseudo-cryptic species within the P. pseudodelicatissima complex[END_REF]Miranda et al., 2018). The study of morphological distinctiveness typically occurs at the static level, but the ontogenetic realm has become especially relevant, as ontogenetic allometries can be useful in a phylogenetic context [START_REF] Bardin | Ontogenetic Data Analyzed As Such in Phylogenies[END_REF]. Allometry, size-related shape changes (Klingenberg, 2016), is a main player in generating biological diversity [START_REF] Esquerré | Evolution of extreme ontogenetic allometric diversity and heterochrony in pythons, a clade of giant and dwarf snakes[END_REF]. Heterochrony, developmental changes in timing of certain events, can contribute to phenotypic and evolutionary changes and lead to speciation [START_REF] Mitteroecker | Heterochrony and geometric morphometrics: a comparison of cranial growth in Pan paniscus versus Pan troglodytes[END_REF][START_REF] Gerber | Mosaic heterochrony and evolutionary modularity: the trilobite genus Zacanthopsis as a case study[END_REF][START_REF] Esquerré | Evolution of extreme ontogenetic allometric diversity and heterochrony in pythons, a clade of giant and dwarf snakes[END_REF]. On the other hand, ontogenetic allometry convergence/divergence can reveal directional selection of shape during development. In sum, a multidimensional (shape, size, time, etc.) analysis of phenotypic data holds potential to interpret speciation events and can provide evidence of ongoing or recent speciation (Hautier et al., 2017;Miranda et al., 2018). In the following article, I present and discuss results that deal with phenotypic differentiation, ontogenetic allometry, and identification of cryptic lineages. I try to stress the importance of such studies for interpreting morphological evolution in the context of phylogenetics and the potential implications of morphological data for species conservation.

Chapter 2: Morphological evolution and convergence

In the previous chapter, I summarized several important concepts to understand the evolutionary history of morphology. An observed morphological pattern gives clues about function and, if thoroughly investigated, about the phylogenetic affinities of a group. However, it is the process by which phenotypes are generated that can ultimately serve to disentangle the evolutionary history of morphological traits. By process, I mean both evolutionary and developmental components of the phenotype that are ultimately interconnected by the information coded in DNA. Nevertheless, the evolutionary/hereditary, developmental, and functional components of the phenotype have not always been well separated during the long documented story of the study of biodiversity, dating back to Ancient Greece.

2.1-Homology and convergence

Under a Darwinian logic, homology has been defined as similarity due to common descent [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. Nevertheless, the definition of this term has been the subject of discussion for many generations (see [START_REF] Hall | Homology : the hierarchical basis of comparative biology[END_REF]. The first formalized definition of homology can be attributed to Richard Owen (Idealistic homology;[START_REF] Wagner | The Biological Homology Concept[END_REF]). Owen's definition of homology did not consider the phylogenetic history between taxa and was based on a "law of nature" (archetype) that established the anatomy of animals and plants [START_REF] Wagner | The Biological Homology Concept[END_REF]. Nevertheless, the use of this concept of homology can be traced back to Aristotle, the first relevant work on this matter consisting on the comparison of the skeleton of a bird and a human, by Belon in the 16 th century [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. Belon illustrated both skeletons identifying each corresponding bone with the same letter, ignoring their shape and functional context within the skeleton.

The identification of each structure was based on topology. Yet, a clear description of homology in the context of natural history only came in the early 19 th century. Étienne Geoffroy Saint-Hilaire was probably one of the first anatomists of the Enlightenment to get a global view of the diversity of vertebrates, much aided by the access to specimens brought to Paris during the Napoleonic Wars [START_REF] Ceriaco | Schweigger's (1812) chelonian types from the extinct eighteenth century Portuguese "Royal cabinet of natural history of Ajuda": some contributions for their identification and nomenclatural implications[END_REF].

As Belon, Saint-Hilaire defined homology based on topology. According to the latter, homologous structures could be identified in morphologically distinct taxa based on their connections to adjacent structures [START_REF] Saint-Hilaire | Philosophie anatomique[END_REF]. Saint-Hilaire's "essential similarity" (homology) principle is based on accepting the existence of a shared structural plan (Bauplan), that can be exemplified by the presence of paired-appendages in animals as different as fish, amphibians, birds, or mammals [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. Belon and Saint-Hilaire's homology can thus be defined as a topological homology that is based on connectivity and results from an atomist approach, which requires the decomposition of biological systems in separate organic structures, so that comparisons can be made in terms of connectivity within that system [START_REF] Rieppel | Atomism, epigenesis, preformation and pre-existence: a clarification of terms and consequences[END_REF][START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. This did not prevent Saint-Hilaire from accepting the importance of functional constraints in anatomy, but allowed him to propose a connection between taxa and reject Cuvier's idea that beings were created to fit perfectly their environment and ecology [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF].

Accepting the idea of a Bauplan, it is pertinent to think that topology only can be safely used to identify homologous traits. However, topology will fail to detect homologies between the supernumerary cervical vertebrae of three-toed sloths [START_REF] Fried | Target finding of pain nerve fibers: neural growth mechanisms in the tooth pulp[END_REF][START_REF] Kumar | TimeTree: a resource for timelines, timetrees, and divergence times[END_REF]Bradypus spp.) and those of two-toed sloths (5)[START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF][START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]Choloepus spp.), or those of the other mammals that present a seven-vertebrae conservative structure of the neck somites [START_REF] Hautier | Skeletal development in sloths and the evolution of mammalian vertebral patterning[END_REF]. Topology on its own cannot test for the hypothesis of homology [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. An alternative to the atomist definition of homology is the concept of epigenetics, in which no single element of a biological system is preformed, with different parts being formed by growth and tissue differentiation [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. During development, complex biological structures can suffer from a rearrangement resulting in a change of the identity of their elements (ontogenetic repatterning; [START_REF] Wake | The linkage between ontogeny and phylogeny in the evolution of complex systems. Complex organismal functions: Integration and evolution in vertebrates[END_REF]. Several cartilage precursors may fuse into a single cartilage, with the resulting bone being generated from a single ossification center [START_REF] Rieppel | Studies on skeleton formation in reptiles. v. Patterns of ossification in the skeleton of Alligator mississippiensis Daudin (Reptilia, Crocodylia)[END_REF]. The original cartilaginous precursors lose their individuality as a result of ontogenetic repatterning. Consider different cartilages ossifying independently as the ancestral state in a given phylogenetic framework. If the pattern observed in the living taxon x is one single bone, an atomist approach would consider that elements were fused, thus allowing to homologize the fused and unfused elements on the basis of topology. From this it would derive a Haeckelian interpretation by which the adult of a "descendent species" would have presented, during embryonic development, structures present in its ancestor adult form that would ultimately become fused (historical homology). Given that cartilaginous precursors lose their identity through ontogenetic repatterning, one cannot homologize the single ossification of the descendent adult with the multiple ossification of the ancestral adult. [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF] used the example of the evolution of the reptilian tarsus and the contrasting ossification pattern when compared to the tetrapod plesiomorphic state presenting multiple elements corresponding to independent ossifications of unfused cartilages. Potential homology can be detected based on topology, but the hypothesis of true homology can only be confirmed through epigenetic reasoning. In the light of evolutionary biology, homology is not a transformation from an ancestral to a derived state. Following von Baer's (1928) view that development is the deviation and differentiation from an ontogenetic Bauplan, homology can be defined as shared developmentally individualized parts of the phenotype (biological homology; [START_REF] Wagner | The Biological Homology Concept[END_REF]. With this, Wagner means that homologous structures between two individuals or within the same individual "share a set of developmental constraints, caused by locally acting self-regulatory mechanisms of organ differentiation".

When defining homology, Owen (1843) also re-adapted the term analogue, which was previously used as a synonymous to homologue by Saint-Hilaire [START_REF] Rieppel | Homology, topology, and typology: the history of modern debates[END_REF]. The definition of an analogue derived from Owen's simplistic definition of its antonym, referring to different structures or organs that fulfill the same functions in two different animals [START_REF] Owen | Lectures on the comparative anatomy and physiology of the invertebrate animals[END_REF]. Following Wagner's concept of biological homology, one can re-define analogy as functionally similar parts of the phenotype subjected to a different set of developmental constraints. In a phylogenetic context, homologous traits that define a monophyletic taxon are called synapomorphies (McGhee, 2011). On the other hand, similarly shaped or functionally equivalent structures that were not inherited from a direct common ancestor are denominated homoplasies. The development of homoplastic traits can happen in three different ways (McGhee, 2011;Fig. 3). When a homoplastic trait arises from developmentally distinct mechanisms involving different ancestral states, it means that a process of convergent evolution generated an analogous structure (McGhee, 2011). DDT is a well-known pesticide to which many arthropods have become resistant [START_REF] Davies | DDT, pyrethrins, pyrethroids and insect sodium channels[END_REF]. This has often occurred through amino acid substitutions in the voltage gate Sodium channel (paralysis locus on the Drosophila melanogaster X chromosome), hindering the binding of the insecticide [START_REF] Davies | DDT, pyrethrins, pyrethroids and insect sodium channels[END_REF]. However, DDT resistance is also achieved by the increased expression of the detoxifying enzyme cythochrome P450 (CYP6G1 gene; [START_REF] Daborn | A single p450 allele associated with insecticide resistance in Drosophila[END_REF]. This is a case of true convergence in the origin of DDT resistance. The second case of homoplasy is parallel evolution. Fresh water three-spine sticklebacks populations are characterized by the independent evolution of a low number of body plates, in contrast with the completely plated marine morph [START_REF] Colosimo | Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles[END_REF]. In most of the low-plated populations, this phenotype resulted from mutations on the Eda gene that led to amino acid changes in Ectodyplasin [START_REF] Colosimo | Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles[END_REF]. This example of parallel evolution shows how the same condition is evolved independently from the same ancestral state [START_REF] Lecointre | The tree of life : a phylogenetic classification[END_REF]McGhee, 2011). The last type of process originating homoplastic traits is reverse evolution [START_REF] Omland | Reconstructing plumage evolution in orioles (Icterus): repeated convergence and reversal in patterns[END_REF]. In this case, trait similarity is not a result of a directly inherited condition but of a reversion of a derived state to the ancestral state. For instance, the evolution of plumage color in orioles (Icterus spp.) shows several cases of reversal [START_REF] Omland | Reconstructing plumage evolution in orioles (Icterus): repeated convergence and reversal in patterns[END_REF].

2.2-Myrmecophagy, a definition

Perhaps one of the most curious cases is that of myrmecophagous mammals. Myrmecophagy or ant-and termite-eating, is a very specialized form of insectivory. Although several mammals include ants and/or termites in their diet, only a few present a stomach content consisting mostly of eusocial insects (>90%; Redford, 1987). Among mammals, myrmecophagy is known to have evolved at least seven times independently (McGhee, 2011). While one may think that ants and termites represent an omnipresent resource and therefore a preferential source of proteins to be exploited by mammals, feeding on eusocial insects requires both compromise and very specialized adaptations (Redford & Dorea, 1984;Redford, 1987). Indeed, the ubiquity of ants and termites must have been a critical factor for the evolution of specialized myrmecophagous mammals, mainly in tropical habitats in which ants appear to occupy the top position in biomass composition in the forest canopy [START_REF] Erwin | Tropical forest canopies: the last biotic frontier[END_REF][START_REF] Adis | Arthropods from the canopy of inundated and terra firme forests near Manaus, Brazil, with critical considerations on the pyrethrum-fogging technique[END_REF]. Such an availability of food items was not only exploited by mammals, but also by reptiles such as the thorny devil (Moloch horridus) and the desert horned (Phrynosoma platyrhinos) lizards, and possibly by Cretaceous theropod dinosaurs like Shuvuuia deserti [START_REF] Chiappe | The skull of a relative of the stem-group bird Mononykus[END_REF][START_REF] Longrich | Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the Alvarezsauridae[END_REF].

On the other hand, preying on ants and termites has several drawbacks. First, ants and termites, with the exception of alate forms and larvae, are not a highly nutritious food source (Redford & Dorea, 1984).

Second, their small size obliges myrmecophagous species to ingest huge amounts of individuals to fulfill their nutritive requirements. While eusociality may be an advantage, as ant nests and termitaria provide a concentrated food source, these insects evolved highly complex defensive mechanisms, such as alarm pheromones, chemical defenses, especially built nests, and a cast system with soldier elements that are responsible for attacking organisms threatening the colony (Redford & Dorea, 1984). Therefore, myrmecophagous species need to be quick both in opening nests and in the ingestion process.

Observations show that attacks to ant or termite colonies are often quick strikes, with predators looking for areas where the soldier concentration is lower (Redford, 1987). Another downside related to the small size of prey item in ant-and termite-eating specialists is the imprecision of the foraging process, with large amounts of inorganic material (i.e., dirt) being ingested (Redford & Dorea, 1984). In addition to low nutrition, small size, and developed defensive strategies, ants and termites, as other insects, present exoskeletons made of chitin, requiring the secretion of large amounts of chitinase enzymes in order to digest these animals (Redford & Dorea, 1984;[START_REF] Emerling | Enamel loss in placental mammals[END_REF].

Diet is a continuous trait and its quantification can be difficult as it can vary due to seasonality or even intraspecific preferences (e.g., Redford, 1987). Many mammal species are found to have ants or termites in their stomachs, even if this might be a result of the ingestion of vegetation or prey items on environments with a large presence of these insects, rather than intentional predation (Redford, 1987). On the other hand, most insects provide an important source of proteins [START_REF] Verkerk | Insect cells for human food[END_REF][START_REF] Bogart | Insectivory of savanna chimpanzees (Pan troglodytes verus) at Fongoli, Senegal[END_REF]. Redford (1987) provides an extensive list of mammals that feed on ants, as well as proxies for the relative importance of these insects in their diets. Rodents provide some least known examples of myrmecophagy like the Dollman's tree mouse (Prionomys batesi), African striped squirrels (Funisciurus spp.), and the shrew-faced squirrel (Rhinosciurus laticaudatus) [START_REF] Davis | Mammals of the lowland rain-forest of north Borneo[END_REF][START_REF] Petter | Dendroprionomys rousseloti gen. nov., sp. nov., rongeur nouveau du Congo (Cricetidae, Dendromurinae)[END_REF][START_REF] Emmons | Ecology and resource partitioning among nine species of African rain forest squirrels[END_REF][START_REF] Denys | First record of the Dollman's tree mouse (Prionomys batesi; Mammalia: Nesomyidae) in the Republic of Congo and additional description of this rare Central African rodent[END_REF]. Carnivores such as the bat-eared fox (Otocyon megalotis) and the sloth bear (Melursus ursinus) feed on ants and termites, although their diets comprise a wider range of items such as other insects, carrion, honey or fruit [START_REF] Kuntzsch | Diet of bat-eared foxes Otocyon megalotis in the Karoo[END_REF][START_REF] Nowak | Walker's Mammal's of the World Volume I[END_REF][START_REF] Sreekumar | Seed dispersal by the sloth bear (Melursus ursinus) in South India[END_REF][START_REF] Stuart | Diet of the bat-eared fox (Otocyon megalotis), based on scat analysis, on the Western Escarpment[END_REF][START_REF] Ramesh | Additional notes on the diet of sloth bear Melursus ursinus in Mudumalai tiger reserve as shown by scat analysis[END_REF]. We here define a myrmecophagous species based on the following criteria: i) ant and/or termites account for 90% or more of the diet based on the volume of stomach content (see Redford (1987), Table I); ii) support for myrmecophagy is based on several references/observations. Additionally, myrmecophagous species present one or more of the following derived features: i) extensible sticky tongues; ii) large salivary glands;

iii) elongated snouts and jaws; iv) tooth loss or reduction in number or structural complexity; v) modified pyloric stomachs (gizzard-like), sometimes with keratinized "pyloric teeth" (Krause & Leeson, 1974) vi) strong claws and forelimbs adapted to dig. Strict/specialized myrmecophagy has independently evolved seven times during the evolution of mammals, one in Monotremata, one in Marsupialia, and five times in Placentalia.

Within Monotremata, the short-beaked echidna (Tachyglossus aculeatus) is an example of strict myrmecophagy [START_REF] Nowak | Walker's Mammal's of the World Volume I[END_REF][START_REF] Phillips | Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas[END_REF]. They present a toothless elongated rostrum, a long and sticky tongue, and powerful digging abilities. The second example of myrmecophagy is a marsupial dasyuromorph, the numbat or banded anteater (Myrmecobius fasciatus; [START_REF] Nowak | Walker's Mammal's of the World Volume I[END_REF]. This monospecific taxon has a diet composed of termites (and occasionally ants) and presents some traits associated to myrmecophagy such as a long tongue and a posteriorly projecting palate [START_REF] Nowak | Walker's Mammal's of the World Volume I[END_REF].

Although numbats present a high number of teeth (up to 52) they are small and simplified, varying in size, and being implanted separate from one another [START_REF] Nowak | Walker's Mammal's of the World Volume I[END_REF].

The most remarkable case of convergent evolution of morphological traits towards myrmecophagy is found within the placental mammals. Adaptation to a myrmecophagous diet evolved in the hyaenid Carnivora (aardwolf; Proteles cristatus), the Pholidota (pangolins), the Tubulidentata (aardvark;

Orycteropus afer), the Cingulata (giant armadillo; Priodontes maximus), and the Vermilingua (anteaters) (Redford, 1987;[START_REF] Nowak | Walker's Mammal's of the World Volume I[END_REF]. All these species present tooth reduction, either in number of complexity (see below), or complete tooth loss (e.g., Davit-Béal et al., 2009). Additionally, to the exclusion of the aardwolf, these taxa share a series of other convergently evolved traits such as elongated rostra and lower jaws, the presence of elongated protractile sticky tongues, powerful forelimbs with strong claws and modified pyloric stomachs that act like a gizzard during food digestion [START_REF] Vizcaíno | Xenarthran biology: past, present, and future[END_REF]Davit-Béal et al., 2009). These and other convergent traits have led to some confusion in the very first descriptions of pangolins, aardvarks, armadillos and anteaters (see above) and continue to be an issue for modern morphology-based phylogenetic analyses (O' Leary et al., 2013;[START_REF] Springer | Technical comment on "The placental mammal ancestor and the post-K-Pg radiation of placentals[END_REF].

2.3-Morphological convergence in myrmecophagous placentals

Before proceeding further into the next article, it is important to make a brief note about the use of terms such as "evolutionary replicate" and "convergence". First, I use the term "replicate" in its sensu lato. [START_REF] Losos | Improbable destinies: fate, chance, and the future of evolution[END_REF] provided an extensive revision of examples of experimental designs that allow to dissect convergent evolution. Along with the many examples presented, the author provided an elegant discussion on the definition of an "evolutionary replicate", a natural or experimental occurrence of repeated evolution at the genetic, morphological, or ecological levels. [START_REF] Losos | Improbable destinies: fate, chance, and the future of evolution[END_REF] discussion accentuates the relevance of scale for the identification of convergent evolution. Secondly, I want to emphasize that the term "convergence" is used here with a broad sense, referring only to the observed phenotypic pattern while ignoring the underlying process.

McGhee (2011) used the myrmecophagous placentals as an example of the role of ecological niche in producing morphologically convergent phenotypes. The selective pressures involved in the adaptation towards myrmecophagy have been so strong that doubts on how to classify ant-and termite-eating placentals remained present for more than 200 years (see "Phylogenetic framework"). [START_REF] Springer | Technical comment on "The placental mammal ancestor and the post-K-Pg radiation of placentals[END_REF] argued that morphological traits often provide less well-supported phylogenetic reconstructions of higher-level relationships, when compared to molecular data. They justify this with the fact that the several habitats occupied by mammals all over the planet present similar conditions. In other words, geographically distant locations may present very similar conditions and their colonization may thus provide "evolutionary replicates". In the morphological tree recovered by O'Leary et al. (2013; Fig. S2), pangolins, aardvarks, and anteaters form a well-supported clade. This is despite the massive number of morphological traits (4541) coded in the supermatrix. These results are a good representation of the degree of morphological convergence in myrmecophagous placentals (Fig. 4).

2.4-Tooth loss

As stressed in the previous sections, the reduction of the dentition is a major feature of myrmecophagous placentals. When Georges Cuvier famously said "Montrez-moi vos dents et je vous dirai qui vous êtes" ("Show me your teeth and I will tell you who you are") he was definitely not thinking of anteaters and pangolins. In such cases, the study of teeth becomes a developmental, rather than a morphological subject.

From the developmental question "How did you lose your teeth?" directly derives an evolutionary perspective: "When, during your evolutionary history, and why?". In this section I provide a brief review of the evolution of teeth in mammals, how they develop, and of our current knowledge about development and morphology in myrmecophagous placentals.

Part of the successful resource exploitation and niche occupation that occurred during the radiation of mammals is due to the mammal chewing system [START_REF] Hemae | Masticatory Function in the Mammals[END_REF][START_REF] Weijs | Evolutionary approach of masticatory motor patterns in mammals[END_REF][START_REF] Ungar | Mammal teeth : origin, evolution, and diversity[END_REF]. Teeth are typically divided in a dorsal crown and ventral roots (one or more). Both parts are composed of dentine, with the crown covered by an enamel layer and the root(s) sheathed with cementum. A hollow chamber in the crown (pulp cavity) is filled with nerves and blood vessels that pass through root canals [START_REF] Ungar | Mammal teeth : origin, evolution, and diversity[END_REF]. These soft tissues make up the pulp branch from the mandibular canal (Ferreira-Cardoso et al., 2019b). Mammals are thecodont, a condition in which teeth are firmly implanted in alveoli. Despite this common structure, variation in shape, size, and number of teeth allowed mammals to improve digestive efficiency and range from dietary specialists to capable generalists. Yet, some mammals lost the ability to form functional teeth, often losing molar occlusion and the ability to crush and grind food items (chewing).

Inefficient or inexistent food processing reduces the assimilation of energy stored in food items (e.g., [START_REF] Morris | Carbohydrate digestion by the domestic cat ( Felis catus )[END_REF][START_REF] Ungar | Mammal teeth : origin, evolution, and diversity[END_REF]. Absence of food processing is therefore a major energetic constraint, and the main reason why myrmecophagous placentals either evolved from lineages with low basal metabolic rates or were subjected to selective pressures in this direction (McNab, 1985;[START_REF] Richardson | Food consumption and seasonal variation in the diet of the aardwolf Proteles cristatus in southern Africa[END_REF].

The tooth development process (odontogenesis) is probably conserved across vertebrates and likely represents the plesiomorphic condition of the group [START_REF] Holland | Gene duplications and the origins of vertebrate development[END_REF][START_REF] Hu | Unique organization of the frontonasal ectodermal zone in birds and mammals[END_REF][START_REF] Rücklin | Development of teeth and jaws in the earliest jawed vertebrates[END_REF]. Depending on the type of tooth (incisor, canine, premolar, molar), this process may show some variations, such as the presence of secondary enamel organs (e.g., multicusped teeth; [START_REF] Jernvall | Tooth shape formation and tooth renewal: evolving with the same signals[END_REF][START_REF] Renvoisé | An Evo-Devo perspective on ever-growing teeth in mammals and dental stem cell maintenance[END_REF]. However, the evolutionary history of mammals shows several exceptional cases of tooth shape simplification (homodonty), enamel loss, reduction of tooth number or complete loss of teeth (Davit-Béal et al., 2009;Meredith et al., 2009). In the case of myrmecophagous placentals, the process of tooth development was either: i) truncated in early stages (e.g., as in anteaters and pangolins), ii) stopped posterior to eruption (e.g., absence of replacement teeth for the anterior dentition of aardvarks), or iii) missed some part of the described traditional steps (e.g., armadillos and sloths). Additionally, the derived hypselodont dentition present in some animals (e.g., xenarthrans and aardvarks) results from a modification in odontogenesis, as at least one cervical loop remains active, with its stem cells differentiating into odontoblasts during the entire lifespan of the animal [START_REF] Renvoisé | An Evo-Devo perspective on ever-growing teeth in mammals and dental stem cell maintenance[END_REF].

Anteaters and pangolins appear to present early stages of tooth development (Gervais, 1867;Rose, 1892;[START_REF] Röse | Uber rudinmentare Zahnanlagen der Gattung Manis[END_REF]Tims, 1908), despite the lack of unequivocal evidence for vestigial teeth. Aardvarks present deciduous teeth that are never replaced (Anthony, 1934b). All xenarthrans and the aardvark present enamel-less teeth (Davit-Béal et al., 2009;Vizcaíno et al., 2009;Meredith et al., 2009). In the following article, osteological correlates of tooth innervation are investigated in order to understand how tooth sensorial function evolved following tooth loss.

In Brief

Tooth loss in anteaters and pangolins represents a textbook example of convergent evolution. Ferreira-Cardoso et al. show that anteaters still present tooth neurovascular systems (dorsal canaliculi) while pangolins do not. As in baleen whales, osseous and neurovascular structures of the anteater mandible were rewired following the loss of teeth.

Loss or reduction of teeth has occurred independently in all major clades of mammals [1]. This process is associated with specialized diets, such as myrmecophagy and filter feeding [START_REF] Dem Er E | Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales[END_REF][START_REF] Meredith | Molecular decay of enamel matrix protein genes in turtles and other edentulous amniotes[END_REF], and led to an extensive rearrangement of the mandibular anatomy. The mandibular canal enables lower jaw innervation through the passage of the inferior alveolar nerve (IAN) [START_REF] Ridgway | Mandibular anesthesia and tooth extraction in the bottlenosed dolphin[END_REF]5]. In order to innervate teeth, the IAN projects ascending branches directly through tooth roots [5,[START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF], bone trabeculae [START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF], or bone canaliculi (i.e., dorsal canaliculi) [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. Here, we used micro-computed tomography (m-CT) scans of mandibles, from eight myrmecophagous species with reduced dentition and 21 non-myrmecophages, to investigate the evolutionary fate of dental innervation structures following convergent tooth regression in mammals. Our observations provide strong evidence for a link between the presence of tooth loci and the development of dorsal canaliculi. Interestingly, toothless anteaters present dorsal canaliculi and preserve intact tooth innervation, while equally toothless pangolins do not. We show that the internal mandibular morphology of anteaters has a closer resemblance to that of baleen whales [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF] than to pangolins. This is despite masticatory apparatus resemblances that have made anteaters and pangolins a textbook example of convergent evolution. Our results suggest that early tooth loci innervation [START_REF] Fried | Target finding of pain nerve fibers: neural growth mechanisms in the tooth pulp[END_REF] is required for maintaining the dorsal innervation of the mandible and underlines the dorsal canaliculi sensorial role in the context of mediolateral mandibular movements. This study presents a unique example of convergent redeployment of the tooth developmental pathway to a strictly sensorial function following tooth regression in anteaters and baleen whales.

RESULTS

Evolution of Dorsal Canaliculi after Tooth Regression

Three-dimensional (3D) models of the mandibles, teeth, and mandibular canals of 26 species were investigated (Figures 1, S1, and S2). Detailed anatomical descriptions of the mandibular canal in each myrmecophagous species and sister taxa are provided as Supplemental Information (Figures S1, Data S1). A summary description of additional species used to reconstruct the ancestral condition of placental mammals is also provided as Supplemental Information (Figure S2, Data S1).

For cetacean comparisons, we used a dataset that was recently published by Peredo et al. [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. All toothed mammals get teeth innervated and vascularized, but this innervation and vascularization only occasionally happens through dorsal canaliculi. These canaliculi correspond to narrow tubular channels that connect the mandibular canal to tooth alveoli (Figures 2E and2F). The teeth of the giant otter shrew (Potamogale velox), the aardwolf (Proteles cristatus), and the dog (Canis lupus) are rooted in close contact with the mandibular canal, with alveoli often surrounded by trabecular bone (Figures 1,S1I, S1J, and S1N). The investigated additional species revealed similar patterns with either deeply rooted teeth or trabeculae surrounding the alveoli (or both; Data S1; Figure S2). These species all lack dorsal canaliculi even for dorsally implanted teeth (e.g., aardwolf molars) (Figure S1I). Dorsal canaliculi were present in three (Pilosa, Cingulata, and Tubulidentata) of the 18 mammals orders sampled (including one marsupial). Ancestral reconstruction unambiguously showed that the absence of dorsal canaliculi likely represents the ancestral condition in placental mammals (Data S1) where alveolar branches (IAN and inferior alveolar artery, IAA) pass through the trabecular structures of the bone or directly through tooth roots. In contrast, armadillos (Dasypus novemcinctus, D. pilosus, and Priodontes maximus), sloths (Bradypus tridactylus and Choloepus hoffmanni), and the aardvark (Orycteropus afer) present dorsal canaliculi (Figures 1,2E, 2F, 3C, 3D, S1, and S4), the so-called ''dorsal branches'' as previously described in baleen whales [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF], whose dorsoventral length increases as the tooth is implanted further from the mandibular canal (Figures 2E and2F). Most of these dorsal canaliculi are located in the anterior part of the mandible, where teeth are reduced or simply missing. In the nine-banded armadillo, we observed one anterior dorsal canaliculus that divides to open in four dorsal foramina (Figures 1 andS1F), while in the hairy long-nosed armadillo, we observed a dorsal canaliculus that divides in a plexus of three branches (Figures 1 andS1G). In the aardvark, three free dorsal canaliculi split and open in six dorsal foramina (Figures 1 andS1M). Intraspecific variation was detected and described (Figure S4; Data S1), but the presence and pattern of dorsal canaliculi is always consistent among specimens. Ontogenetic variation was studied in two species of sloths in which fetuses display dorsal canaliculi associated with vestigial tooth loci (Figures 3A and3B). These dorsal canaliculi are still present in adults of both species despite the resorption of vestigial teeth (Figures 3C and3D).

Surprisingly, toothless species (anteaters and pangolins) display contrasted mandibular canal morphologies (Figures 1 and2). All three investigated anteater species present dorsal canaliculi that open in small foramina (Figures 2A-2C and S1A-S1C). These foramina are placed along the anterior flattened dorsal margin of the mandible, which defines the dental pad, with only limited intraspecific and bilateral variations among specimens of the three species (Figure S4). Ontogenetic variation is equally limited, with similar patterns of dorsal canaliculi being observed in both adults and juvenile giant anteaters (M. tridactyla, Figure S4L-S4N) and nine-banded armadillos (D. novemcinctus, Figures S4A-S4F). Conversely, pangolins lack dorsal canaliculi (Figure 2D), with only several minute canaliculi that are parallel to the mandibular canal, both dorsally and ventrally, but rarely connected to it (Figures S1D andS1E). Foramina associated to these parallel canaliculi are scarce, invisible to the naked eye, and only occasionally open dorsally to the mandibular canal.

Histological Evidence for the Passage of Nerves and Blood Vessels in Dorsal Canaliculi 3D analyses were complemented by histological series, which enabled to identify internal soft structures associated to the dorsal canaliculi. The LFB (see Method Details) stained histological slices of the collared anteater (T. tetradactyla) mandible enabled us to describe the soft tissues encapsulated in the mandibular canal (Figure 4). We observed dorsal canaliculi that allow for the passage of an ascending branch of the inferior alveolar nerve (IANab; Figures 4C and4C'), of the inferior alveolar artery (IAAab; Figure 4C), and of the inferior alveolar vein (IAVab; Figure 4B'). In T. tetradactyla, a keratinous dental pad (pa) covers the dorsal part of the mandible (Figure 4C). Ventrally, the epidermis (ep) consists of a small layer (Figure 4C), which lies dorsally to a thick dermis layer (de; Figure 4C). In addition to connective tissue, this dermis layer presents small blood vessels and nerve branches. Histological slices of bowhead whale [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF] (Figure S3A) show a similar structuration of soft tissues, with accessory branches of the large IAN and IAA that most likely connect the mandibular canal to the vestigial tooth alveoli through dorsal canaliculi. The histological section [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF] suggests a pronounced anterior projection of the dorsal canaliculi, similar to the pattern for the IAN ascending branches in odontocetes [START_REF] Ridgway | Mandibular anesthesia and tooth extraction in the bottlenosed dolphin[END_REF]. Circular timetree (according to Kumar et al. [9]) with corresponding 3D reconstructions of the internal mandibular morphology with dorsal canaliculi (orange), mandibular canal (cyan), mental branches (purple), and teeth (dark blue). Tree branches are colored in orange (presence of dorsal canaliculi) and black (absence of dorsal canaliculi). Animal silhouettes are colored in black (sampled species) and gray (species from [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]). See also Figures S1,S2, S4, and Data S1.

Current Biology 29, 468-475, February 4, 2019

DISCUSSION

Shadows of Regressed Tooth Buds in Dorsal Canaliculi

Enamelless sloths, armadillos, and aardvarks all present dorsal canaliculi that are associated with either tooth alveoli or vestigial tooth loci in the anterior part of the mandible. The corresponding nervous and vascular ascending branches should then be considered homologous to alveolar branches. If the number and shape of alveolar branches can vary [START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF][START_REF] Kieser | The course and distribution of the inferior alveolar nerve in the edentulous mandible[END_REF], especially in terminal bifurcations, each main alveolar branch usually corresponds to a single tooth root [START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF]. Establishing the direct homology between ascending and alveolar branches in anteaters is hindered by the absence of teeth. However, their closest relatives, sloths and armadillos, as well as the aardvark, also display some anterior dorsal canaliculi with no apparent connection to tooth alveoli (Figures 1,2, and S1). Long-nosed armadillos present dorsal canaliculi in the anterior part of the mandible and the anterior most alveoli, while sloths present minute dorsal canaliculi in cheek teeth. This suggests that dorsal canaliculi likely evolved concomitantly with tooth simplification in cingulatans and pilosans. All these species have been shown to display vestigial tooth buds in the anterior part of the mandible during pre-natal development [START_REF] Hautier | The hidden teeth of sloths: evolutionary vestiges and the development of a simplified dentition[END_REF][START_REF] Martin | Tooth development in Dasypus novemcinctus[END_REF][START_REF] Anthony | La dentition de l'oryct erope. Morphologie, d eveloppement, structure, interpr etation[END_REF]. The observed pattern of anterior dorsal canaliculi in long-nosed armadillos (Dasypus) and the aardvark roughly matches the distribution of previously described vestigial teeth [START_REF] Martin | Tooth development in Dasypus novemcinctus[END_REF][START_REF] Spurgin | Enamel in the teeth of an embryo edentate (Dasypus novemcinctus linn)[END_REF][START_REF] Thomas | A milk dentition in Orcyteropus[END_REF][START_REF] Lo ¨nnberg | On a new Orycteropus from Northern Congo and some remarks on the dentition of the Tubulidentata[END_REF]. In nine-banded armadillos, we found dorsal canaliculi that consistently split into three to six distinct dorsal foramina in the anterior part of the mandibles (Figure 1, S1F, and S4A-S4F), while Martin [13] identified five to six vestigial incisors. This difference is not surprising given the frequent dental formula variation observed in nine-banded armadillos [START_REF] Ciancio | Evolutionary implications of dental eruption in Dasypus (Xenarthra)[END_REF]. The observed variation in dorsal canaliculi count of anteaters and nine-banded armadillos (Figure S4) was to be expected as the number and shape of alveolar branches vary in humans [START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF][START_REF] Kieser | The course and distribution of the inferior alveolar nerve in the edentulous mandible[END_REF], both at the intraspecific and bilateral levels. This variation also matches the variation observed in tooth count of placentals showing a reduced dentition such as the aardvark [START_REF] Anthony | La dentition de l'oryct erope. Morphologie, d eveloppement, structure, interpr etation[END_REF], long-nosed armadillos [START_REF] Ciancio | Evolutionary implications of dental eruption in Dasypus (Xenarthra)[END_REF] and the giant armadillo [START_REF] Vizcaı ´no | Paleontological Society The Teeth of the '' Toothless. Novelties and Key Innovations in the Evolution of Xenarthrans[END_REF]. Such bilateral variation in tooth number might result from the lack of stabilizing selection due to an absence of strict occlusion, as hypothesized for mysticetes [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF]. In the aardvark [START_REF] Thomas | A milk dentition in Orcyteropus[END_REF], the lower milk dentition is normally composed of eight to ten teeth, with the second generation of teeth varying from five to eight in number depending on the presence of vestigial anterior premolars and canines [START_REF] Thomas | A milk dentition in Orcyteropus[END_REF][START_REF] Lo ¨nnberg | On a new Orycteropus from Northern Congo and some remarks on the dentition of the Tubulidentata[END_REF]. We found dorsal canaliculi that could correspond to two-four anterior premolars, one canine, and three incisors (Figure S1M). This number coincides with the deciduous dental formula of the aardvark [START_REF] Anthony | La dentition de l'oryct erope. Morphologie, d eveloppement, structure, interpr etation[END_REF]. Our observations therefore provide convincing evidence for a link between the presence of teeth, vestigial or not, and the development of dorsal canaliculi.

This developmental link was corroborated by the study of ontogenetic series of both extant sloth genera. Comparisons between sloth pre-and post-natal stages allowed us to directly Current Biology 29, 468-475, February 4, 2019 associate one long anterior dorsal canaliculus to a vestigial tooth locus (Figure 3), which is resorbed during development and is absent in adults. Based on histological sections (Figure 4), we showed that ascending branches of the IAN and IAA pass through dorsal canaliculi in the collared anteater (T. tetradactyla). Teeth innervation was likely retained after tooth resorption in all pilosans, and this could extend to all xenarthrans if we consider the anterior dorsal canaliculi of armadillos as representatives of vestigial tooth loci. Wadu et al. [START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF] showed that human tooth nerve bundles can also be retained-although slightly reduced-after tooth loss induced by senescence. Our observations of histological sections of toothless whale fetuses (see [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF] and Data S1, Figure S3) suggest that vestigial tooth loci are associated to IAN and IAA ascending branches during development, a situation that mirrors the condition observed in toothed cetaceans [START_REF] Ridgway | Mandibular anesthesia and tooth extraction in the bottlenosed dolphin[END_REF]5]. Ridgway et al. [4] described an elongation of the ascending branches of the inferior alveolar nerve in dolphins, while an anterodorsal inclination was also reported for the dorsal canaliculi of mysticetes [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. However, the homology between alveolar branches and ascending branches carried by dorsal canaliculi was recently challenged for whales [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. Instead, Peredo et al. [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF] proposed that dorsal canaliculi and associated foramina constitute a derived character of crown Mysticeti since no in-ternal evidence of such a structure was visible in other edentulous taxa [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. Our results clearly contradict this assertion, as we showed that anteaters display both foramina and dorsal canaliculi. In our view, the ascending branches of IAN and IAA should be considered as homologous to alveolar branches since they include identical structures and are linked to the development of teeth. This implies that dorsal canaliculi evolved convergently in xenarthrans, aardvarks, and baleen whales following tooth reduction.

Unlike the other toothless species investigated, pangolins do not present dorsal canaliculi in their mandibles. The small parallel canaliculi (Figures S1D andS1E) present a distinct shape and topology hindering a hypothetical homology with the dorsal canaliculi. Tims [START_REF] Tims | Tooth-vestiges and associated mouth parts in the Manidae[END_REF] reported the presence of 13-14 tooth rudiments in the mandible of M. javanica, which he also compared to hair follicles. However, the observed number of up to four tooth vestiges per coronal slice [START_REF] Tims | Tooth-vestiges and associated mouth parts in the Manidae[END_REF] seems inconsistent with the position of the teeth along an anteroposterior axis. Unless M. javanica presents four tooth generations, no more than two tooth buds should be expected for each coronal slice [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF][START_REF] Ishikawa | Development and physiological degradation of tooth buds and development of rudiment of baleen plate in southern minke whale, Balaenoptera acutorostrata[END_REF]. In this context, the 13-14 teeth reported by Tims [START_REF] Tims | Tooth-vestiges and associated mouth parts in the Manidae[END_REF] should be considered with caution and might correspond to distinct structures. The lack of tooth buds [START_REF] Rose | Beitrage zur Zahnentwicklung der Edentaten[END_REF] might therefore explain the absence of dorsal canaliculi. Although an early dental lamina may be present in pangolin embryos [START_REF] Spurgin | Enamel in the teeth of an embryo edentate (Dasypus novemcinctus linn)[END_REF][START_REF] Tims | Tooth-vestiges and associated mouth parts in the Manidae[END_REF], its development appears to be drastically reduced when compared to anteaters [START_REF] Rose | Beitrage zur Zahnentwicklung der Edentaten[END_REF]. On the other hand, the lack of these structures in pangolins could be explained by phylogenetic constraints. Since dorsal canaliculi are also absent in carnivorans (Figures 1, S1I, and S1J), their absence might represent the ancestral state for Ferae (Pholidota + Carnivora). Additionally, complete tooth loss probably happened much earlier in pangolins than in anteaters, since the almost certainly toothed most recent common ancestor (MRCA) of Pilosa (58 Mya [START_REF] Gibb | Shotgun mitogenomics provides a reference phylogenetic framework and timescale for living xenarthrans[END_REF]) is much more recent than the MRCA of Ferae (80 Mya [START_REF] Meredith | Impacts of the Cretaceous terrestrial revolution and KPg extinction on mammal diversification[END_REF]). With the oldest fossil pangolin (45 Mya [START_REF] Gaudin | The phylogeny of living and extinct pangolins (Mammalia, Pholidota) and associated taxa: a morphology based analysis[END_REF]) being already toothless, the absence of dorsal canaliculi in pangolins might simply reflect a more ancient tooth loss. Importantly, our study shows that the external resemblances of the mandibles in anteaters and pangolins, which made them a textbook example of convergent evolution, have overshadowed the complex evolution of their internal morphology. Functional Role of Dorsal Canaliculi in Toothless Species Previous studies proposed that mammalian teeth might play a sensorial role in detecting a wide array of external stimuli including pressure, proprioception, and percussion [START_REF] Nweeia | Sensory ability in the narwhal tooth organ system[END_REF] in addition to their role for food intake. Our results suggest that the development of dorsal canaliculi might be linked to the presence of tooth loci/ vestigial teeth in both anteaters and baleen whales. One puzzling fact however is that the development of vestigial teeth remained preserved for so long during the evolutionary history of these taxa. In sloths, Hautier et al. [START_REF] Hautier | The hidden teeth of sloths: evolutionary vestiges and the development of a simplified dentition[END_REF] showed that the mineralization and resorption of the vestigial teeth is an integral part of prenatal dental development. Given the conservatism of sloth dental formula in the fossil record [START_REF] Gaudin | Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence[END_REF], they proposed that these vestiges were kept for at least 30 million years [START_REF] Gibb | Shotgun mitogenomics provides a reference phylogenetic framework and timescale for living xenarthrans[END_REF][START_REF] Gaudin | Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence[END_REF], which implies that there is still a strong selective pressure for developing these structures. Such a complex and energetically costly developmental pathway might be the consequence of a strong developmental constraint in preserving the associated innervation and vascularization of the mandible. A similar developmental constraint was proposed for the initial development of a normal eye in blind cavefish [START_REF] Casane | Evolution of eye development in the darkness of caves: adaptation, drift, or both?[END_REF]. These fish present normal eye development before showing sign of later degeneration. Given that there is no separation between cells giving rise to the retina and to the forebrain at the early stage of the nervous system (neural plate stage), the development of a viable embryo with a well-formed forebrain implies the early development of the eyes [START_REF] Casane | Evolution of eye development in the darkness of caves: adaptation, drift, or both?[END_REF]. Tooth innervation develops synchronously with tooth development, being controlled by local molecular signals [START_REF] Fried | Target finding of pain nerve fibers: neural growth mechanisms in the tooth pulp[END_REF]. We therefore argue that tooth development, even in initiation stages, might be required for maintaining the dorsal innervation of the mandible. As a matter of fact, embryos of pygmy anteaters present early tooth development (dental lamina-tooth buds) [START_REF] Rose | Beitrage zur Zahnentwicklung der Edentaten[END_REF][START_REF] Gervais | Zoologie et pal eontologie g en erales: nouvelles recherches sur les animaux vert ebr es vivants et fossiles[END_REF].

Histological slices allowed revealing the presence of dorsal projections of the IAN and IAA passing through the dorsal canaliculi in a mandible of the collared anteater. We propose that these structures respectively innervate and vascularize the mandibular keratinous pad that covers most of the dorsal margin of the horizontal ramus (Figure 4C). The oral sensory receptors that project via the IAN (a branch of the trigeminal nerve) may confer a somatosensory role to the mandibular keratinous pad. In fact, the pattern of innervation of this keratinous pad resembles that of bird beak [START_REF] Kuenzel | Neurobiological basis of sensory perception: welfare implications of beak trimming[END_REF]. Both structures display a superficial keratinous layer followed dorsally by epidermis and a large dermis with blood vessels and free nerve endings [START_REF] Kuenzel | Neurobiological basis of sensory perception: welfare implications of beak trimming[END_REF] (Figure 4). Early tooth development (bud stage) was previously reported in anteaters [START_REF] Rose | Beitrage zur Zahnentwicklung der Edentaten[END_REF]. In birds, the keratinous ramphoteca was proposed to be responsible for the early interruption of odontogenesis at the lamina stage [START_REF] Louchart | From snout to beak: the loss of teeth in birds[END_REF]. An early keratinization might be the triggering event for subsequent odontogenesis disruption during the development of both anteater keratinous pad and bird beak. Interestingly, toothless whales also present keratinous structures (baleens) that develop after odontogenesis interruption [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF]. Thewissen et al. [10] argued that tooth development is a sine qua non condition to the development of baleens. This is in line with both fossil and molecular evidence suggesting a stepwise transition between teeth and baleen in mysticetes [START_REF] Dem Er E | Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales[END_REF]. Ekdale et al. [32] also recently suggested that foramina for baleen vascularization in the upper jaw of toothless whales are likely homologous to tooth alveoli. Similarly, odontogenesis and associated dorsal canaliculi might be a prerequisite for mandibular keratinization in anteaters. Accordingly, the lack of keratinous pad and vestigial teeth might explain the absence of dorsal canaliculi in pangolins.

In rorqual whales, the peculiar distribution of dorsal canaliculi along the mandible was proposed to be related to movement coordination of lower jaws and alignment with the baleen plates during filter feeding [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. Pyenson et al. [33] argued that nerves passing through the most anterior canaliculus connected the brain to a symphyseal organ/vibrissae system responsible for mandibular motor coordination and prey detection, respectively. Given the absence of external vibrissae in anteaters and the fact that they mainly use olfaction to detect their prey [START_REF] Lubin | Defenses of Nasutitermes termites (Isoptera, Termitidae) against Tamandua anteaters (Edentata, Myrmecophagidae)[END_REF], dorsal canaliculi and respective extensions of the IAN are unlikely related to prey detection. However, several studies [34 and references therein] described the synchronization between tongue protrusion and mandible closing during feeding in anteaters (i.e., Myrmecophaga and Tamandua) as well as in ant-eating echidnas. In these groups, the mandibles rotate medio-laterally, with the oral cavity widening when the tongue is retracted and narrowing when it is protruded, forming a tubelike mouth to serve as physical support [START_REF] Naples | Morphology, evolution and function of feeding in the giant anteater (Myrmecophaga tridactyla)[END_REF][START_REF] Endo | Macroscopic and CT examinations of the mastication mechanism in the southern tamandua[END_REF]. This type of integrated movement would require a tactile feedback originating from the dorsal margin of the mandible, which is in contact with the protruding tongue and the upper jaw. A similar hypothesis has been proposed in whales [START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF] for the coordination between mandibles and baleens during gulping. Tooth pulp stimulation was shown to trigger a response of the digastric muscle in cats [START_REF] Boissonade | Responses of trigeminal brain stem neurons and the digastric muscle to tooth-pulp stimulation in awake cats[END_REF]. Dong et al. [38] also showed that cat teeth stimulation results in discharge signatures for different textures (e.g., rough or smooth). Furthermore, teeth are known to respond to nonpainful stimuli in humans [START_REF] Chatrian | Electrical stimulation of tooth pulp in humans. II. Qualities of sensations[END_REF]. We propose that the ascending branches of the IAN might be part of the somatosensory system involved in mechanoreception, which could explain the convergent evolution of dorsal canaliculi in the toothless mandibles of baleen whales and anteaters. In contrast, no medio-lateral rotation of the mandibles was reported in pangolins [START_REF] Endo | Macroscopic and CT examinations of the mastication mechanism in the southern tamandua[END_REF], while the presence of a fused symphysis likely helps maintaining the tube-like shape of the oral cavity while feeding [START_REF] Endo | The functional anatomy of the masticatory muscles of the Malayan pangolin, Manis javanica[END_REF]. Compared to anteaters and baleen whales, such a relatively reduced mandibular mobility could potentially explain the absence of dorsal canaliculi in pangolins.

Our results support the hypothesis of convergent exaptation of the dorsal canaliculi in anteaters and baleen whales following tooth regression. We unequivocally showed that the IAN as well as blood vessels branch through the dorsal canaliculi and argue that keratinous structures and vestigial teeth have a crucial role in mandibular innervation, maintaining the sensorial function associated to the presence of teeth while strong selective pressures induced their loss. Despite the superficial resemblance of the masticatory apparatus between anteaters and pangolins, convergent tooth loss resulted in divergent structures in the internal morphology of their mandible. We propose that these differences likely reflect divergent phylogenetic histories and/or divergent functional constraints. Rewiring of the mandibular canal in anteaters and baleen whales provides a striking example of evolutionary tinkering linked to the regression of teeth. marsupials) -Dasyurus hallucatus. Using this dataset, we were able to compare the morphology of the mandibular canal and dorsal canaliculi of closely related toothed and toothless taxa, as well as a wide range of species belonging to 18 mammalian orders. We additionally compared our results to the previously published research on cetaceans and even-toed ungulates (Cetartiodactyla) by Peredo et al. [7]. We segmented a total of five D. novemcinctus, three M. tridactyla (two adults + one juvenile), three T. tetradactyla, and two Cy. didactylus in order to account for intraspecific variation (Data S1, Figure S4). We also segmented left and right hemi-mandibles of the anteater specimens to assess the level of bilateral variation in dorsal canaliculi count (Data S1). Both fetus and adult specimens of B. tridactylus and Choloepus spp. were studied (Figure 3) in order to seek the presence of a dorsal canaliculus linked to the development of vestigial teeth [START_REF] Hautier | The hidden teeth of sloths: evolutionary vestiges and the development of a simplified dentition[END_REF] and to confirm that there was no major variation in the number of dorsal canaliculi through ontogeny. Mandibles were chosen to study dental innervation patterns because they are composed by a single bone (dentary) enclosing the IAN and the IAA. The mandibular canal soft tissues enter in a continuous canal posterior to the tooth row and project anteriorly to its anterior end. Compared to the cranium, all branching patterns of the mandibular canal are therefore more easily traceable. The mandible is, therefore, a simpler model to study innervation patterns with the techniques used for this manuscript. 40-150 kV). The scan resolution differed according to the size of specimens (Table S1). Eight specimens were obtained from MorphoSource (https://www.morphosource.org), one from Digimorph (www.digimorph.org), and one from the Digital Morphology Museum (http://dmm4.pri.kyoto-u.ac.jp/dmm/WebGallery/index.html). The left hemi-mandibles (the right one was used if the left one was missing or broken) were reconstructed, with respective mandibular canals and teeth. Avizo 9.4.0 (Visualization Sciences Group) was used to perform the 3D reconstructions. When teeth were absent, the mental branches were distinguished from the dorsal canaliculi by their larger diameter and their lateral projection to the mental foramina on the lateral aspect of the mandible [5,[START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF]. Dorsal canaliculi were defined as dorsal projections of the mandibular canal opening on the dorsal surface of the mandible.

Acquisition of data

Histology

We also dissected the head of an adult specimen of T. tetradactyla (ISEM 778N) fixed in formalin. The right mandible was extracted and its associated musculature removed. The mandible was then subjected to decalcification during forty five days, following standard protocols. A portion of the mandible was then cut (as shown in Figure 4A) with the use of a scalpel, and fixed in paraffin. Serial slicing was performed to produce 3mm thick coronal and sagittal sections of the mandible. Luxol Fast Blue (LFB) was used to stain the slices in order to allow for the blue staining of the myeline sheaths insulating nerve cell axons. The LFB staining protocol was composed of several phases (1)[START_REF] Dem Er E | Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales[END_REF][START_REF] Meredith | Molecular decay of enamel matrix protein genes in turtles and other edentulous amniotes[END_REF][START_REF] Ridgway | Mandibular anesthesia and tooth extraction in the bottlenosed dolphin[END_REF](5)[START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF][START_REF] Peredo | Alveoli, teeth, and tooth loss: Understanding the homology of internal mandibular structures in mysticete cetaceans[END_REF][START_REF] Fried | Target finding of pain nerve fibers: neural growth mechanisms in the tooth pulp[END_REF][START_REF] Kumar | TimeTree: a resource for timelines, timetrees, and divergence times[END_REF][START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF][START_REF] Kieser | The course and distribution of the inferior alveolar nerve in the edentulous mandible[END_REF] in which acetic acid (10%), Luxol Fast Blue (0.1%), lithium carbonate (0.05%), and cresyl violet (0.1%) were used. (1) Histological sections were placed in a sealed container with the Luxol Fast Blue solution and were left overnight inside an oven at 58 C; (2) Sections were rinsed with ethanol (96%); (3) Sections were rinsed with distilled water; (4) Sections were differentiated in a lithium carbonate solution during 30 s; (5) Sections were placed in a rack with ethanol (70%) and were then stirred manually twice during periods of 15 s; [START_REF] Wadu | Morphological variability of the human inferior alveolar nerve[END_REF] Sections were placed in a rack with distilled water and were then stirred manually during 1 min; (7) A counterstain was performed by placing the sections in a cresyl violet solution during 10 min; (8) Samples were quickly rinsed twice with ethanol (96%); [START_REF] Kumar | TimeTree: a resource for timelines, timetrees, and divergence times[END_REF] Sections were placed on ethanol (100%) for two periods of 2 min each; [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF] Sections were placed on xylene (dimethylbenzene) for the same duration as in step ( 9); [START_REF] Kieser | The course and distribution of the inferior alveolar nerve in the edentulous mandible[END_REF] Sections were mounted with a resinous medium (Pertex). A histological slice of a coronal section of the mandible of Balaena mysticetus (provided by J.G.M. Thewissen [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF]) was used for anatomical comparisons (Figure S3A).

2.5-Morphological adaptation of the head musculature

Ecological convergence is often coupled with both behavioral and morphological convergence (e.g., [START_REF] Stuart-Fox | Sex-specific ecomorphological variation and the evolution of sexual dimorphism in dwarf chameleons (Bradypodion spp.)[END_REF]McGhee, 2011). In an evolutionary context, a replicate is therefore expected to show a correlation between behavior, ecology, and morphology [START_REF] Johnson | Behavioral convergence and adaptive radiation: effects of habitat use on territorial behavior in Anolis lizards[END_REF][START_REF] Losos | Improbable destinies: fate, chance, and the future of evolution[END_REF]. Function overlaps with behavioral, ecological, and morphological realms of evolution. The exploitation of an ecological niche is associated to the evolution of specific morphologies that correlate to function, which is often associated to behavior. For instance, the morphological evolution of the skull of durophagous bats of the genus Chiroderma is associated with the exploitation of a specific ecological niche (grain eating) within the phylogeny of fruit bats [START_REF] Nogueira | Ecomorphological analysis of the masticatory apparatus in the seed-eating bats, genus Chiroderma (Chiroptera: Phyllostomidae)[END_REF]. On the other hand, morphology can be a correlate of function. Nogueira et al. (2009) showed that bite force was relatively weak in long-snouted nectarivorous bats when compared to their insectivorous sister taxa. The authors showed that low bite forces were associated with morphological traits such as elongated rostra and narrow zygomatic arches. Hautier et al. (2012) showed differences in the skull and mandibles of hystricognathous rodents associated to dietary strategies, which they associated to the origin and insertion of masticatory muscles (function). The authors also show a morphological convergence associated to habitat (niche exploitation). These are just a few examples of shape-function interactions during processes of adaptive evolution toward an ecological niche. The literature presents numerous studies addressing convergent evolution of shape and function (e.g. [START_REF] Herrel | Omnivory in lacertid lizards: adaptive evolution or constraint?[END_REF][START_REF] Stayton | Testing hypotheses of convergence with multivariate data: morphological and functional convergence among herbivorous lizards[END_REF]Wroe & Milne, 2007;[START_REF] Tseng | Testing adaptive hypotheses of convergence with functional landscapes: a case study of bonecracking hypercarnivores (AA Farke[END_REF][START_REF] Tseng | A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters[END_REF].

In the majority of these studies, the concept of "constraint" is omnipresent. Often, function or functional proxies (e.g., muscle volume) are less correlated with shape than hypothetically assumed [START_REF] Figueirido | Constraint and adaptation in the evolution of carnivoran skull shape[END_REF][START_REF] Fabre | Do muscles constrain skull shape evolution in strepsirrhines?[END_REF]. Adaptation can be overlain by phylogenetic constraints [START_REF] Stayton | Morphological evolution of the lizard skull: a geometric morphometrics survey[END_REF]Hautier et al., 2012). In other cases, morphology and function appear to be decoupled from behavior [START_REF] Smith | The anatomy and function of the feeding apparatus in two armadillos (Dasypoda): anatomy is not destiny[END_REF]. Given the complexity of morphological traits, one is confronted with the need to study convergent adaptive evolution as a continuous trait (e.g., magnitude of convergence; [START_REF] Stayton | Testing hypotheses of convergence with multivariate data: morphological and functional convergence among herbivorous lizards[END_REF][START_REF] Martinez | Convergent evolution of an extreme dietary specialisation, the olfactory system of worm-eating rodents[END_REF][START_REF] Arbour | Tail weaponry in ankylosaurs and glyptodonts: an example of a rare but strongly convergent phenotype[END_REF] and to consider convergence as a plastic concept that is susceptible to scale and level of analysis [START_REF] Losos | Improbable destinies: fate, chance, and the future of evolution[END_REF]. In such scenario, are there true evolutionary replicates? The answer to this question is dependent on another one: "is adaptation perfect?" [START_REF] Travis | Adaptation[END_REF] answered this question by splitting traits between adaptive and non-adaptive ones. The latter are normally referred to as "constraints". Phenotypic traits may tend to an optimum, as groups of adaptive traits are acted on by natural selection, but organismal integration (inter-trait covariation/correlation) caused by the common pathways between adaptive and non-adaptive traits will restrict that optimum [START_REF] Travis | Adaptation[END_REF]. Therefore, evolutionary replicates may present variable degrees of convergence. As a result, the dissection of cases of evolutionary convergence may result in one conclusion: each level (ecological, morphological, and functional) depends on the extent of phenotypic evolvability allowed by the adaptive/non-adaptive trait correlation specific to each clade, as well as to the ability to detect and quantify variation. Aspects related to phenotypic integration are developed in chapter 3.

Muscles are responsible for motion of skeletal elements and soft tissues in animals [START_REF] Rizzo | Fundamentals of anatomy and physiology[END_REF].

Therefore, functional adaptation is often assessed or described on the basis of muscular anatomy (Naples, 1985(Naples, , 1986(Naples, , 1999b;;Endo et al., 1998[START_REF] Endo | Comparative functional morphology of the masticatory apparatus in the long-snouted crocodiles[END_REF]Marshall, 2009), biomechanical models [START_REF] Weijs | Biomechanical models and the analysis of form: a study of the mammalian masticatory apparatus[END_REF][START_REF] Gueldre | Biomechanics of the masticatory apparatus of Pteropus giganteus (Megachiroptera)[END_REF]Fabre et al., 2017), and muscle performance [START_REF] Herrel | Sexual dimorphism of head size in Gallotia galloti : testing the niche divergence hypothesis by functional analyses[END_REF][START_REF] Santana | Mechanics of bite force production and its relationship to diet in bats[END_REF]Ginot et al., 2018). The mammalian skull is a highly modular system in which developmental and functional constraints interact to limit or promote the evolution of certain axes of variation (e.g., Hallgrímsson et al., 2004;Goswami, 2006;Porto et al., 2009; see 'Morphological evolution, integration and modularity' section). One of the main epigenetic factors generating covariance during the ontogeny of complex skeletal structures is muscle-bone interactions (Cheverud, 1982a;Hallgrímsson et al., 2007;Zelditch et al., 2008). Muscular activity during the embryonic development of the skull applies mechanical forces on both bones and cartilages (Hall & Herring, 1990;Herring, 1993).

Those forces, or mechanical loading, act on the embryonic solid surfaces influencing the direction, and amount of growth or compression (Herring, 1993). The absence of muscular contraction during embryonic development results in skeletal anomalies including the loss and reduction of certain bones and cartilages (Hall & Herring, 1990;Rot-Nikcevic et al., 2006;Anthwal, Peters, & Tucker, 2015). Muscular activity has been detected in development as early as during the differentiation of myoblasts in muscle precursors [START_REF] Natsuyama | In utero behavior of human embryos at the spinal-cord stage of development[END_REF]. This shows that the generation of covariance on the skull through muscle-bone interactions happens much earlier than functional movements like sucking or chewing.

Evidence of the role of muscular contraction in bone morphology is exemplified by the casestudies presented by Anthwal et al. (2015) and Herring (1993). Anthwal et al. (2015) used a knockout experiment to show that the initiation of coronoid growth in the mouse mandible is dependent on the expression of the transcription factor Pax9. However, the subsequent growth of the coronoid process is also dependent on the activation of Sox9 expression by the application of mechanical loading. The expression of some growth-related genes is activated by mechanical loading [START_REF] Hatton | A short pulse of mechanical force induces gene expression and growth in MC3T3-E1 osteoblasts via an ERK 1/2 pathway[END_REF]. In mutants with a reduced temporalis (the muscle attaching on the coronoid process), the coronoid was vestigial and eventually lost in later ontogenetic stages [START_REF] Aggarwal | Mesodermal Tbx1 is required for patterning the proximal mandible in mice[END_REF]). In the second example, [START_REF] Herring | Functional design of cranial muscles comparative and physiological studies in pigs[END_REF] showed that the masseter of pigs, one of the muscles originating on the jugal, presents a posterodorsal extension on the zygomatic arch, when compared to their sister clade, the peccaries. This muscular projection is matched by posterior process of the jugal. Herring (1993) suggests that the posterior extension of the masseter induced the development of this jugal process. Such a process is similar to that studied by Anthwal and colleagues (2015). These two examples are illustrative of the importance of muscle development in skull evolution.

Despite its role in early development, mechanical loading is often considered an important motor of covariance generation during the postnatal life of mammals [START_REF] Herring | Strain in the braincase and its sutures during function[END_REF][START_REF] Zelditch | Developmental regulation of skull morphology II: ontogenetic dynamics of covariance[END_REF]Hallgrímsson et al., 2007). Shifts in covariance just posterior to weaning were partly associated to muscular activity in the cotton rat skull, although other factors may also play an important role (Zelditch & Carmichael, 1989). On the other hand, a transition from weaning to a hard food diet is probably responsible for a shift in direction of the ontogenetic trajectory of phenotypic covariance in mice (Mitteroecker & Bookstein, 2009). The magnitude and direction of mechanical loading is not constant during an animal's lifespan [START_REF] Sun | Cranial sutures and bones: growth and fusion in relation to masticatory strain[END_REF]. This likely contributes to the repatterning of covariation at different stages of postnatal development (Mitteroecker & Bookstein, 2009). When considering shifts of muscular strain (either magnitude or direction) in postnatal life, muscle-bone interactions in the skull can be interpreted as an environmental factor (at least partially; Herring, 1993). This is because functional movements are dependent on the type of diet (hard or soft). Mechanical loading is therefore a critical factor of skull shape from the first appearance of muscle anlagen in the embryo, and may change patterns of covariance during adult life.

Given the intimate association between musculature and skull shape, it is highly relevant to analyze these two systems in the context of adaptive evolution. In the case of convergent evolution towards myrmecophagy, qualitative and quantitative analyses of the muscles of the masticatory apparatus can shed light on the functional adaptation of ant-and termite-eating placentals (Endo et al., 1998(Endo et al., , 2007(Endo et al., , 2017;;Naples, 1999b;Reiss, 2001). Additionally, comparative anatomy of auxiliary mastication, tongue, and hyoid muscles can provide a better view over the similarities and differences in functional morphology across myrmecophagous placentals. Ultimately, this type of information constitutes an essential asset to test functional convergence in the skull of ant-and termite-eaters.

In the following article I describe the masticatory apparatus, the transverse mandibular musculature, and the muscles of the hyoid, thyroid, the sternum, and the face in anteaters. I additionally compare their muscular anatomy to descriptions of other myrmecophagous placentals available in the literature.

Introduction

The Cretaceous terrestrial revolution and the Cretaceous-Paleogene (K-Pg) mass extinction event are often viewed as milestones in placental mammal evolution (Meredith et al., 2011). These events promoted the opening of terrestrial ecological niches available to placentals, contributing to their morphological diversification [START_REF] Romer | Vertebrate paleontology[END_REF][START_REF] Alroy | The fossil record of North American mammals: evidence for a Paleocene evolutionary radiation (P Waddell, Ed.)[END_REF]. The adaptation of the placental masticatory apparatus likely contributed to this radiation, as mechanical processing of food items is essential to ensure a better energetic intake (Hiiemae, 2000).

Dietary specialization is often a main driver of cranial morphological specialization [START_REF] Varrela | Effects of attritive diet on craniofacial morphology: a cephalometric analysis of a Finnish skull sample[END_REF]Barlow, Jones, & Barratt, 1997;Nogueira, Peracchi, & Monteiro, 2009;Hautier, Lebrun, & Cox, 2012;[START_REF] Klaczko | Are diet preferences associated to skulls shape diversification in xenodontine snakes? (AR Evans[END_REF][START_REF] Maestri | Diet, bite force and skull 139 morphology in the generalist rodent morphotype[END_REF]. The masticatory apparatus of placental mammals is composed by the temporal and pterygoid fossae, and the zygomatic arch of the skull, by the jaws, and by a series of mostly adductor muscles responsible for mandibular movements involved in the chewing process (Hiiemae, 2000;[START_REF] Hylander | Functional anatomy and biomechanics of the masticatory apparatus. Temporomandibular Disorders: An Evidenced Based Approach to Diagnosis and Treatment[END_REF]. This apparatus is composed by the temporal, the masseter, and pterygoid muscles [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF]. These powerful muscles are derived from the plesiomorphic "adductor mandibulae" plate of sarcopterygians [START_REF] Edgeworth | The cranial muscles of vertebrates[END_REF][START_REF] Diogo | Head and neck muscle evolution from sarcopterygian fishes to tetrapods, with a special focus on mammals[END_REF]. Although several other muscles contribute to mastication, the mandibular movement is mainly operated by the elevator forces of the temporal and masseter, the mandibular protrusion mainly involve the pterygoids and the masseter, and condylar stability is provided by the pterygoids and the zygomaticomandibularis [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF]Naples, 1999;[START_REF] Hylander | Functional anatomy and biomechanics of the masticatory apparatus. Temporomandibular Disorders: An Evidenced Based Approach to Diagnosis and Treatment[END_REF]. The homogeneity in the composition of the masticatory apparatus contrasts with the broad morphofunctional disparity of the placental skull. This functional diversity is mostly reflected by differences in muscle morphologies and proportions. These are often associated with phylogenetic constraints and ecological specialization [START_REF] Parsons | Myology of rodents. Part II. An account of the myology of the myomorpha, together with a comparison of the muscles of the various suborders of rodents[END_REF][START_REF] Druzinsky | Mammalian masticatory muscles: homology, nomenclature, and diversification[END_REF]Hautier et al., 2012;Fabre et al., 2017;Ginot, Claude, & Hautier, 2018).

The evolution of myrmecophagy (ant-and termite-eating) in mammals is a textbook example of morphological convergence driven by diet (McGhee, 2011) leading to modified skulls with tooth reduction, extreme snout elongation, and long extensible tongues [START_REF] Rose | [END_REF]Davit-Béal et al., 2009;Ferreira-Cardoso et al., 2019;[START_REF] Gaudin | Evolution & morphology[END_REF]. Morphological changes driven by the adaptation to myrmecophagy even led some myrmecophagous placentals, as anteaters, pangolins, or giant armadillos, to lose the ability to chew (Naples, 1999;Davit-Béal et al., 2009;Vizcaíno et al., 2009). Aardvarks, on the other side, are still able to chew (Patterson, 1975). Anteaters (Vermilingua, Xenarthra) consist of up to ten extant species included in two molecularly divergent families that diverge more than 37 million years ago (Mya; Gibb et al., 2016), the Cyclopedidae (seven Cyclopes spp.) and the Myrmecophagidae (two Tamandua spp. and M. tridactyla) (Gaudin & Branham, 1998;Gibb et al., 2016;Miranda et al., 2018). All species display a unique combination of morphological traits such as a complete tooth loss, an unfused mandibular symphysis, an extremely reduced mandibular coronoid process, and an elongated tongue. These features and concomitant loss of mastication have been the target of several studies dedicated to the anatomy and function of their cephalic musculature (Owen, 1856;[START_REF] Macalister | Report on the anatomy of insectivorous Edentates[END_REF]Redford, 1987;Reiss, 1997Reiss, , 2001;;Naples, 1999;Endo et al., 2007Endo et al., , 2017)).

The degree of variation in shape, size, and architecture of masticatory, hyoid, and thyroid musculature across the three anteater genera has not been fully addressed, despite the morphological divergence of skull and mandible shape between Cyclopes and myrmecophagids. The extreme elongation of the myrmecophagid rostrum and the loss of the jugal bone in Cyclopes are illustrative examples of the contrasts between taxa with similar diets and food ingestion strategies [START_REF] Montgomery | Cyclopes didactylus (tapacara, serafin de platanar, silky anteater)[END_REF][START_REF] Montgomery | Movements, foraging and food habits of the four extant species of Neotropical vermilinguas (Mammalia; Myrmecophagidae)[END_REF]. A comprehensive comparative description of the masticatory apparatus of the Vermilingua is a prerequisite to shed light on the diversity of functional morphology among myrmecophagous placentals. Here, we describe the masticatory muscles in the three anteater genera Cyclopes¸ Tamandua, and Myrmecophaga (Gaudin & Branham, 1998). We used a combination of traditional and virtual dissections to accurately measure muscular mass and volumes, while reconstructing 3D surfaces based on iodine-enhanced µCTscanning (e.g., [START_REF] Gignac | Iodine-enhanced micro-CT imaging: methodological refinements for the study of the soft-tissue anatomy of post-embryonic vertebrates[END_REF]Ginot et al., 2018). Our study aims to provide the first thorough description of the anteater masticatory apparatus and to compare it to those of other myrmecophagous placentals (pangolins and aardvarks). We further hope to contribute to an accurate baseline for future biomechanical studies.

Materials and methods

Biological sampling

We dissected specimens from the three extant anteater genera: Cyclopes didactylus (n = 2); Tamandua tetradactyla (n = 3); Myrmecophaga tridactyla (n = 1). C. didactylus and T. tetradactyla specimens were roadkill while M. tridactyla was a zoo specimen. All wild specimens were collected in French Guiana and were stored in the collections of the Institut Pasteur de la Guyane (IPG; JAGUARS collection, Cayenne, France) and the Institut des Sciences de l'Evolution (ISEM; Montpellier, France). C. didactylus and one specimen of T. tetradactyla (UM-778-N) were collected and immediately fixed in a 10% formaldehyde solution. M. tridactyla and another specimen of T. tetradactyla (M-3074) were collected and frozen. M-3075 (T. tetradactyla) was collected and immediately dissected. All heads were extracted, as well as the complete sternum and the tongue musculature that were also detached when possible (M-1525, M-3075).

Frozen and fresh heads were then fixed in a 10% formaldehyde solution. All specimens were stored in 70% ethanol.

Dissections

For each specimen, only one side was dissected. The areas of insertion and origin were described and each muscle was then stored separately in a 70% ethanol solution. All muscles were weighted with a Sartorius A 120 S precision weighing scale (precision = 0.01mg). Measurements for all specimens are given on Table S1.

Iodine-enhanced CT-scanning

The most complete and well-preserved specimen from each species was selected to be stained. The three specimens were µCT-scanned prior to staining, so that the bone tissue could be easily reconstructed. A second scan was performed after specimens were stained (see below). High-resolution microtomography (µCT) was performed at Montpellier Rio Imaging (MRI; Microtomograph RX EasyTom 150, X-ray source 40-150 kV) platform. Scan resolutions are provided in Table 2.

The contrast enhancement protocol was adapted from [START_REF] Cox | Reviewing the morphology of the jaw-closing musculature in squirrels, rats, and guinea pigs with contrast-enhanced microCT[END_REF]. All specimens were placed in a solution of iodine (5% I2KI) for a period of two to eight weeks, depending on size. This concentration represents a trade-off between observed staining efficiency and the soft-tissue shrinkage associated with iodone staining, even if incubation period seems to have a limited effect in soft-tissue shrinkage, after the first two days [START_REF] Vickerton | Concentration-dependent specimen shrinkage in iodine-enhanced microCT[END_REF]). In T. tetradactyla and M. tridactyla¸ small volumes of I2KI solution were injected directly in the muscles, as the large size of the specimens hinders an efficient passive diffusion of the contrast agent.

The contrast-enhanced scans were imported to Fiji (Schindelin et al., 2012) and 2-fold binning was performed in order to allow for a better handling of the three-dimensional (3D) volumes. The reconstruction of the 3D volumes was performed using Avizo 9.7.0. The volumes were extracted for each muscle. Contrast-enhanced µCT-scans results in an increase of density of the soft tissues and thus the contrast between muscles and bone is lost [START_REF] Cox | Reviewing the morphology of the jaw-closing musculature in squirrels, rats, and guinea pigs with contrast-enhanced microCT[END_REF]. Therefore, the skull volume was reconstructed from a CTscan prior to staining. We generated surfaces for the skull and muscles separately and then used the function "register" in Avizo 9.7.0 to align these reconstructions. Most tendons and aponeuroses were not stained by the iodine solution, and were therefore not reconstructed. Some muscles may thus appear detached from the skull (e.g., masseter superficialis in myrmecophagids).

We tried to reconstruct the maximum muscles related to the masticatory, facial, hyoid/thyroid and sternum musculature in each species. This was highly dependent on specimen condition at the time of skinning and on the staining results. In M. tridactyla, only the suprahyoid musculature was reconstructed and described.

Nomenclature

We follow the muscular nomenclature for the masticatory apparatus of xenarthrans defined by Naples (1985) based on the dissection of the two extant sloth species (Choloepus hoffmanni and Bradypus variegatus). This terminology adapted previously existing nomenclature for other mammals [START_REF] Rinker | The comparative myology of the mammalian genera Sigmodon, Oryzomys, Neotoma, and Peromyscus (Cricetidae)[END_REF][START_REF] Turnbull | Mammalian masticatory apparatus[END_REF]. The most recent thorough description of the cranial and tongue musculature of the giant anteater (Naples, 1999) followed the same terminology used in Naples (1985). More recent descriptions of the masticatory apparatus of M. tridactyla and T. tetradactyla adopted the English version of the same terminology (Endo et al., 2007(Endo et al., , 2017)). We also follow Naples (1999) nomenclature for the muscles associated to the tongue, the hyoid apparatus (suprahyoid and infrahyoid muscles), and the facialmasticatory muscles. We here modified the designation of the facial nasolabialis into maxillolabialis. All Table 1 -Masticatory muscle volumes (up; mm 3 ) and percentages (down) obtained from the 3D models of the contrast-enhanced specimens segmentation. TStemporalis superficialis; pz-TS -temporalis superficialis pars zygomatica; pm-TP -temporalis profundus pars medialis; pl-TP -temporalis profundus pars lateralis; MP -masseter profundus; MS -masseter superficialis; ps-PE -pterygoideus externus pars superior; pi-PE -pterygoideus externus pars inferior; pa-PM -pterygoideus medius pars anterior; pp-PM -pterygoideus medius pars posterior.

Table 2 -Facial-masticatory muscle volumes (left; mm 3 ) and percentages (right) obtained from the 3D models of the segmentation of the contrast-enhanced specimens. pe-B -buccinatorius pars externa; pi-B -buccinatorius pars interna; MA -mandibuloauricularis.

Facial-masticatory muscle volume (mm 3 )

Facial-masticatory muscle proportion (%)

Results

Measurements of the muscles involved in mastication are summarized in Tables 1 and2. Volume measurements were performed on the segmented muscles of the contrast-enhanced specimens. Mass measurements of all dissected specimens are provided in Tables S1 andS2. Below, we provide an anatomical description of the musculature of each of the three species in our study. The description is followed by a comparative anatomy section in which muscle shape, size (Tables 1 and2), and architecture are compared among anteaters. Anatomical structures of the skull, mandible, hyoid-thyroid, and sternum that are relevant to the description are depicted on figures 1, 2, and 3.

Anatomical description

Cyclopes didactylus

Masticatory apparatus

Masseter superficialis

The masseter superficialis (MS; Fig. 4) is the only muscle of the masseter muscle complex present in C.

didactylus. The MS is anteroposteriorly elongated and originates from the lateral surface of the zygomatic process of the maxilla. Its origin consists of a long and strong posteroventrally projecting tendon that covers the most anterior half of the muscular part. The muscular part of the MS can be divided in two parts (Fig. 4; Fig. S1A). The pars anterior of the MS (pa-MS), which is covered by the tendon laterally, inserts laterally from the posterior part of the dentary pad (Fig. 1B) to the anterior margin of the condyle.

The pa-MS presents a pars reflexa inserting on the ventral margin of the ascending ramus of the mandible extending anteroposteriorly from the anterior margin of the coronoid process to the level of the mandibular canal. The pars posterior of the MS (pp-MS) covers the pa-MS posteriorly to the coronoid process and inserts on the angular process of the mandible (Fig. 4). Its pars reflexa is continuous with the pars reflexa of the pa-MS and almost reaches the most posterior point of the angular process. The fibers of the MS have an anteroposterior orientation, being more gradually oblique anteriorly close to the tendon.

Temporalis superficialis

The temporalis superficialis (TS; Fig. 4) is the largest of the four muscles of the temporal complex. It is a fan-shaped muscle that originates from a scar along the dorsal edge of the temporal fossa. The temporal crest runs from the posterior end of the orbital ridge to the anterior surface of the root of the zygomatic process of the squamosal. A thick tendinous layer streches from the origin of the TS and covers the posterodorsal part of the muscle. The TS is thinner at its origin and thicker at its insertion. The insertion is muscular on the dorsal tip and the dorsal part of the posterior margin of the coronoid process. An aponeurosis runs dorsoventrally along the anterior surface of the TS and completely covers the lateral and anterior surfaces of the coronoid process. The fibers of the TS are organized in a bipennate structure (Fig. S1B). Deep fibers are dorsomedially oriented while superficial ones are dorsolaterally oriented. In cross section, the insertion angle of medial fibers with the axis of pennation is about 26°, while lateral fibers present and angle of around 12°.

Temporalis profundus pars lateralis

The temporal complex includes a deep component divided in two parts, the temporalis profundus pars lateralis (pl-TP; Fig. 5A) being the largest. The pl-TP takes its origin on a pseudoelliptical area that extends from the posteroventral part of the orbital contribution of the frontal to the anteroventral part of the temporal fossa. The insertion of the pl-TP covers most of the posterolateral surface of the coronoid process, and narrows posteriorly stretching along the dorsal depression located between the coronoid process and the condyle. Contrary to the TS, the pl-TP does not present a pennate structure, with fibers roughly vertically oriented.

Temporalis profundus pars medialis

The temporalis profundus pars medialis (pm-TP; Fig. 5A) consists on the inner part of the TP that takes its origin from the orbit, between the ventral edge of the temporal fossa and the orbital/rotundum foramina.

The anterior portion of the pm-TP is anastomosed with the pl-TP. However, the separation between both parts is clear posteriorly on the insertion, with the posterior tip of the pm-TP occupying a more ventromedial position at the level of the mandibular foramen. Fiber orientation and shape of the pi-TP is similar to that of pe-TP, but the former's volume is about two thirds that of the latter.

Temporalis superficialis pars zygomatica

The temporalis superficialis pars zygomatica (pz-TS; Fig. 4A,C) is a relatively small muscle, which is well separated from the TS. It originates from the ventromedial part of the zygomatic process of the squamosal and broadens ventrally to end on an anteroposteriorly elongated muscular insertion. The insertion occupies the lateral part of the mandibular notch. The pz-TS is wider dorsally and thinner ventrally, with fibers presenting an oblique orientation.

Pterygoid externus pars superior

The pterygoid externus pars superior (ps-PE; Fig. 4B and5A) is a small anteroposteriorly elongated muscle. The ps-PE arises from a fossa that extends from the ventral part of the parietal, at the lower limit of the temporal fossa, into the glenoid fossa. It is the only part of the pterygoid muscle complex that takes its origin outside the pterygoid fossa. The muscle is mediolaterally compressed and obliquely oriented. Its posterior part presents a small torsion anterior to its ventrolateral projection towards the mandible. The insertion of the ps-PE consists of a small concavity just medioventrally to the head of the articular condyle.

Pterygoideus externus pars inferior

The pars inferior of the PE (pi-PE; Figs. 4B and5A) is similar in shape with the ps-PE. The pi-PE originates from a small area in the sphenoid, laterally to the foramen rotundum, and dorsally adjacent to the origin of the pterygoideus medius. The muscle is mediolaterally wide and presents a more horizontal orientation than the ps-PE. The muscle projects posterolaterally to insert on the anterior margin of the articular condyle, at mid-height. The medial part of the pi-PE projects posteriorly, inserting below the insertion area of the ps-PE, reaching the mid-length of the head of the condyle.

Pterygoideus medius

The pterygoid medius (PM; Figs. 4 and5) arises from the pterygoid fossa and consists of a fleshy block that originates from the posterolateral part of the palatine to the level of the anterior margin of the ectotympanic. Its fibers run anteroposteriorly with an oblique orientation and insert medially on the angular process of the mandible, from the level of the anterior margin of the head of the articular condyle to its posterior margin. In the most posterior part of their insertion, the fibers assume a more posteroventral direction and form a small pars reflexa that wraps the posteriormost tip of the angular process. A dense connective tissue lies dorsally to the insertion of the pterygoideus medius, posterior to the opening of the mandibular canal.

Facial-masticatory musculature

Buccinatorius pars externa

The buccinatorius pars externa (pe-B; Fig. 4A,C,D) is distinguishable from the internal part of this muscle. It is a sheet-like muscle that envelopes the external surface of the buccinatorius pars interna. Its origin stretches along the ventral edge of the maxilla and the palatine, from anteriorly to the inferior orbital foramen until the anterior part of the insertion of the pterygoideus medius. The ventral part of the pe-B wraps the ventral portion of the buccinatorius pars interna and attaches on a broad insertion area on the lateral surface of the mandible. The fibers have a dorsoventral direction.

Buccinatorius pars interna

The pars interna of the buccinatorius muscle (pi-B; Fig. 4B) is more voluminous when compared to the pars interna. The pi-B originates from a thin fiber bundle posterior to the buccal commissure and is covered by the pe-B just posteriorly. It is a long muscle that reaches as far posteriorly as the level of the coronoid process. The pi-B is characterized by a triangular-shaped buccal projection that sits between the upper and the lowers jaws. The lateral part of the pi-B contacts the pe-B and does not attach to any bone surface. Posteriorly, the pi-B inserts on the dorsomedial surface of the mandible, along the fossa located between the posterior part of the dentary pad and the coronoid process. Its insertion ends posteriorly to the coronoid process where it contacts the temporalis profundus pars medialis and the anterior part of the pterygoid medius. The fibers of the pi-B are anteroposteriorly oriented.

Facial musculature

Dilator nasi

The dilator nasi (DN, Fig. 6E,F) is sheet-like, becoming thinner and narrower anteriorly. It takes its origin on the posterodorsal part of the maxilla, anterior to the lacrimal bone. The insertion of the muscle is tendinous and was not preserved in the specimens. The fibers are anterodorsally directed and horizontally oriented.

Maxillolabialis superficialis pars superior

The maxillolabialis pars superior (ps-MLs; Fig. 6E) originates more posterodorsally than the DN, with some fibers arising from the lacrimal and the frontal bone. However, most of the area of origin is on the maxilla. The muscle becomes narrower anteriorly and its anterior portion is linked to a tendon that inserts anteriorly in the lip region. The tendon, unfortunately, is invisible in the iodine-stained specimen. This muscle covers the origin of the dilator nasi, and the maxillolabialis profundus pars superior. It overlies most of the anterodorsal part of the maxilolabialis profundus pars inferior.

Maxillolabialis profundus pars inferior

The maxillolabialis profundus pars inferior (pi-MLp; Fig. 6E,F) is the longest labial muscles. It takes its origin on the posterodorsal margin of the cranium, stretching from the ventralmost point of the maxillalacrimal suture to about two third of the height of the lacrimal. The muscle is flat posteriorly and becomes narrower and triangular in cross-section, anteriorly. The pi-MLp narrows anteriorly with slightly oblique fibers attached to a tendon, close to the buccal commissure. This muscle is overlain by the pars superior of the MLp and a small ventral part of the posterior part of the maxillolabialis pars pars profunda.

Maxillolabialis profundus pars superior

The maxillolabialis pars profunda is the smallest part of the labial muscle complex (ps-MLp; Fig. 6F). It is a tape like muscle with the origin just dorsal to the origin of the maxillolabialis pars inferior, being slightly overlain by the latter. The tendon for the insertion of the ps-MLp is not preserved in this specimen.

Nevertheless, given the position of the muscle, the anteroposteriorly directed fibers were probably horizontally oriented.

Intermandibular musculature

Intermandibularis anterior

The transversus mandibularis (IA; Fig. 7) is a thin, dorsolaterally wide, and elongated muscle. Naples (1999a) described this muscle as the anterior part of the mylohyoideus pars anterior. The IA takes its origin on the cartilage of the unfused mandibular symphysis. The muscle has two insertions on the ventrolateral margin of both hemimandibles, wrapping around their ventral edges. In ventral view (Fig. 7B), it covers the anterior part of the base of the tongue and the anterior part of the geniohyoideus (see 'Hyoid, thyroid, and cricoid musculature'). The IA extends posteriorly for about half the length of the mandible, its posterior end being clearly separated from the anterior margin of the mylohyoideus pars anterior (see 'Intermandibular musculature'). Its fibers are transversely oriented and are continuous between mandibles, with this muscle consisting of one single element.

Mylohyoideus pars anterior

The mylohyoideus pars anterior (pa-Mh; Fig. 7) consists of a fibrous sheet that originates ventrally to the dentary pad, on the medial surface of the mandible. This muscle is homologous to the pars medius of the mylohyoideus described by Naples (1999a). The origin area stretches from the widest point of the dentary pad to its posteriormost point. Posteriorly, its origin shifts from the mandible to the ventromedial surface of the pterygoideus medius (PM). At the posterior end of the PM the origin changes again, creating a dorsolateral gap separating the anterior and the posterior fibers. We consider this to be the posterior limit of the pa-Mh, with the posterior part being considered the mylohyoideus pars posterior. The fibers are transversely oriented ventrally and insert along a fibrous midline raphe that connects the left and right pa-Mhs (Fig. S1C).

Mylohyoideus pars posterior

The mylohyoideus pars posterior (pp-Mh; Fig. 7) is continuous with the pa-Mh. The division between the two parts is set by the difference of the origin. The pp-Mh mylohyoideus takes its origin on the ventromedial surface of the tympanic bulla, parallel to the auditory tube. The fibers display the same orientation as in the pars anterior and insert on a fibrous midline raphe. However, near the posterior end of the hard palate, the left and right muscles appear to anastomose in the midline, with the intertonguing contact becoming less spaced. As the interstylohyoideus and the posterior part of the mylohyoideus pars posterior were not preserved in our specimens of C. didactylus, the attachment of the pp-Mh to the hyoid system is not visible.

Hyoid, thyroid, and cricoid musculature

Geniohyoideus

The geniohyoideus (GH; Figs. 7 and8) has a tendinous origin and arises from the mandibular symphysis cartilage. The GH is a very long and dorsoventrally compressed muscle that rests ventral to the base of the tongue and dorsal to the transversus mandibularis (anteriorly) and the mylohyoideus (posteriorly). The tendon is about half the length of the mandible, with the horizontally oriented muscular fibers originating at the level of the caudal palatine foramen. In ventral view, the anterior part of the GH is pointy, widening posteriorly until it anastomoses with its symmetric counterpart. The right and left bellies are anatomosed from the posterior part of the palatine to the basisphenoid-presphenoid suture. Posteriorly, the two muscles present a fibrous connection, but the bilateral elements are clearly separated (Fig. 7). The GH passes just ventrally to the ventral part of the epihyal and the ceratohyal and inserts along the posterolateral surface of the basihyal. The most lateral part of the muscle has a small insertion on the most ventral part of the thyrohyal. The fibers of the GH are horizontally oriented throughout its entire length.

Ceratohyoideus

The ceratohyoideus (CeH; Fig 8A ,B,D,E) is a small hyoid muscle with a subtriangular shape in lateral view. It takes its origin on the depression of the lateral surface of the thyrohyal bone, ventral to its anterodorsal process. Its obliquely oriented fibers are anteroposteriorly short and project anteroventrally to insert on a fossa on the posterior surface of the epihyal. This muscle has no clear homologous in other mammals [START_REF] Greene | Anatomy of the rat[END_REF]Naples, 1999). It might be homologous to the stylohyoideus of cetaceans [START_REF] Reidenberg | Anatomy of the hyoid apparatus in Odontoceti (toothed whales): specializations of their skeleton and musculature compared with those of terrestrial mammals[END_REF].

Thyrohyoideus

The thyrohyoideus (ThH; Fig. 8A,B,D,E) covers most part of the lateral surface of the thyroid cartilage.

It originates on a dorsoventral scar along the posterior part of the thyroid and its obliquely oriented fibers insert on the concave ventral edge of the thyrohyal.

Cricothyroideus pars recta

The pars recta of the cricothyroideus (pr-CTh; Fig. 8B,D,E) is a sheet like muscle with its origin at the posterior margin of the cricoid cartilage, stretching from its most ventral point to its mid-height. The pr-CTh is composed of horizontally oriented fiber bundles that insert on the posterolateral surface of the thyroid cartilage, posterior to the origin of the ThH. The insertion area is most posterior ventrally and extends anterodorsally, being slightly overlain by the dorsal part of the ThH.

Cricothyroideus pars obliqua

The cricothyroideus pars obliqua (po-CTh; Fig. 8A,D) corresponds to the medial part of the pr-CTh. The two parts anastomose at their origin. The po-CTh consists of an extremely thin inner sheet that extends anterodorsally. Its insertion is located dorsally on the thyroid cartilage and accompanies the shape of its dorsal border. Only the dorsal part of the po-CTh is exposed laterally, giving it a fan-like aspect anteriorly.

The remaining dorsal portion of the muscle is overlain by pr-CTh. As for the pars recta, the name of the po-CTh derives from the orientation of its fibers.

Cricoarytenoideus posterior

The arytenoid cartilage is the insertion area of a few small muscles that originate posteriorly on the cricoid cartilage (Fig. 2). The cricoarytenoideus posterior is the most dorsal muscle (CaP; Fig. 8C,F,D). This muscle is small and pseudorectangular in dorsal view. This thick sheet of muscular fibers originates on the posterodorsal surface of the cricoid cartilage and its fibers run posteroanteriorly to reach the arytenoid cartilage, anteroventrally. The anterior part of the CaP becomes thinner and hard to distinguish from the remaining muscles that attach to the arytenoid cartilage.

Cricoarytenoideus lateralis

The muscle attaches the arytenoid cartilage from the lateral surface of the cricoid cartilage (CaL; Fig. 8D,F) and takes its origin dorsally to that of the cricothyroideus complex. In lateral view, the CaL is covered by both the latter and the posterior process of the thyroid cartilage. The fibers of this small fleshy muscle are obliquely oriented and insert ventrally to the CaP. The anterior part is not clear on the iodine stained µCT scan, which suggests that the tendinous insertion occurs roughly at the level of the anterior part of the CaP.

Thyroarytenoideus pars lateralis

The thyroarytenoideus pars lateralis (pl-Tha; Fig. 8C,F) is the largest muscle attaching to the arytenoid cartilage in C. didactylus. It occupies approximately one third of the volume inside the thyroid cartilage and covers most of its concave medial wall. In lateral view, the muscle is semicircular in shape. The pl-Tha fibers are dorsoventrally oriented, the anterior ones bending anteriorly at the midlength. The origin of the pl-Tha consists of a shallow and short anteroposteriorly elongated scar at the base of the thyroid cartilage. Ventrally, the pl-Tha inserts laterally on the arytenoid cartilage.

Thyroarytenoideus pars medialis

The thyroarytenoideus pars medialis (pm-Tha; Fig. 8F) corresponds to a small and extremely thin part with a fiber arrangement similar to that of the pl-Tha. It originates posteriorly and is parallel to the posterior fiber of the pars anterior. The pm-Tha shares a similar origin with that of the pl-Tha, between the latter and the trachea. However, both parts are separated by a sheet of conjunctive tissue from the origin to the insertion. Anterodorsally, the fibers appear to insert on a ventral projection of the arytenoid cartilage.

Pharynx musculature

Tensor veli palatini

The tensor veli palatine (t-VP; Fig. 8B,D,E,F) is a very thin ribbon-like muscle posteriorly adjacent to the levator veli palatini. Its fibers run obliquely from the lateral to the medial edges of the pterygoid bone shelf, dorsal to the auditory tube. Anteroposteriorly, the t-VP stretches from the level of the anterior margin of the external auditory meatus to the opening of the auditory tube. Anteriorly, the t-VP is adjacent to the posterior part of the origin of the pterygoideus medius (PM) while posteriorly it is connected to the origin of the levator veli palatini.

Levator veli palatini

The levator veli palatini (l-VP; Fig. 8) originates on the ventral surface of the posterior part of the pterygoid process. At the origin, the l-VP is flat and resembles the shape of the t-VP. Anteriorly the l-VP is thin and strap-like, while posteriorly it forms a fleshier bundle. The fibers run medially from a small origin area to insert on the soft palate just a few millimeters posteroventrally. The l-VP meets the anterior part of the medialis veli palatini. Its fibers slightly bend posteriorly and become parallel to the medialis veli palatini (Fig. 8F).

Medialis veli palatini

In C. didactylus, the medialis veli palatini (m-VP; 8B, E, F) is a strap of longitudinally running fibers.

The muscle is flat at its origin on the soft palate and becomes fleshier and narrower posteriorly. The m-VP is about the same length as the l-VP (≈ 5mm) and makes up the central axis of the oropharynx. Most of the muscles and tissues surrounding the m-VP were too damaged to be described.

Stylopharyngeus

The stylopharyngeus was badly damaged during the dissection. The muscle is illustrated (Sph; Figs. 8C and 9A) but a formal description cannot be given.

Constrictores pharyngeus

The constrictores pharyngeus were badly damaged during the dissection. The muscle is illustrated (CP;

Figs. 8C and9A) but a formal description cannot be given.

Sternum musculature

Sternomandibularis

The origin of the sternomandibularis (Sm; Fig. 9) is located anterodorsally on anterodorsal surface of the manubrium. The fibers of this elongated muscle are anteroventrally directed and form a tape-like element.

The Sm is mediolaterally wide and has a tendinous insertion on the ventral margin of the mandibular ramus, with a small portion wrapping around to attach on the lateral surface. The posterior part and origin of the Sm were not preserved in the stained specimen.

Sternoglossus

The sternoglossus (Sg; Fig. 9) is the longest of all the muscles in C. didactylus. It originates on the cartilaginous xiphisternum (not visible on the stained specimen). The posterior half of the Sg is strap-like and follows a parallel direction to the trachea. It flanks the hyoid apparatus, to which it is attached, at the level of the thyrohyoid, by some muscular fibers that connect the enveloping conjunctive tissue. Anterior to the hyoid apparatus, the Sg cross-section becomes elliptical and enters the base of the tongue anterior to the epihyal. As it enters the mouth, the sternoglossus cross-section becomes cylindrical in shape. Its diameter reduces as it projects anteriorly, with the anteroposteriorly oriented fibers progressively unwrapping from the muscular bundle to cover the epidermal wall of the tongue. At the level of the orbital foramen, the Sg loses its shape original, which gives a whip-like aspect to its buccal portion.

Sternothyroideus

The sternothyroideus (Sth; Figs. 8 and9) arises from the sternum at the level of the second and third ribs.

It fuses to its bilateral counterpart just anteriorly to the second rib. The Sth is anteroposteriorly elongated as the Sm and the Sg. In contrast, the Sth is less strap-like, with its cross-section being pseudo-rectangular.

The obliquely oriented fibers end anteriorly on a tendinous insertion of the posteroventral part of the base of the thyroid cartilage.

Tamandua tetradactyla

Masticatory apparatus

Masseter superficialis

The masseter superficialis (MS; Fig. 10) is a fleshy anteroposteriorly long muscle; it is pseudorectangular in shape in lateral view. The fibers of the MS are slightly oblique and take their origin on the lateral surface of the zygomatic process of the maxilla through a strong tendon. The MS inserts on the shallow masseteric fossa of the mandible. It covers most of the lateral surface of the ascending ramus, including most of the more anterior masseter profundus (see below). The MS is thicker posteriorly, and thins down anteriorly as it overlies the masseter profundus. The tendon of the MS was not visible in the contrast-enhanced specimen. The MS presents a pars reflexa that runs from the level of the posterior part of the jugal to the posterior tip of the angular process of the mandible. The pars reflexa attaches to the ventral surface of the masseter profundus anteriorly. Anteriorly, the MS presents a small projection towards the zygomatic process of the mandible.

Masseter profundus

The masseter profundus (MP; Figs. 5B and 10) is smaller than its superficial counterpart (MS). It takes its origin on the anterior part of the ventromedial surface of the jugal bone. Anteriorly, its origin area includes the most posteroventral surface of the zygomatic process of the maxilla. The fibers of the MP run obliquely to insert posteroventrally on the lateral surface of the mandible. The fibers are more vertical than those of the MS. The muscle presents a lateral and a slight anterior component to their orientation. The insertion area on the mandible stretches from the coronoid process to the level of the sphenopalatine foramen.

Contrary to the MS, the MP is thicker at its origin than at its insertion.

Temporalis superficialis

The temporalis superficialis (TS; Fig. 10) is one of the three muscles that forms the temporal complex. It is also the largest, arising from a relatively large surface between the dorsal edge of the temporal fossa and the origin of the pterygoideus externus pars superior (Fig. 10). It is wide and broad in lateral view, and transversely compressed. It presents a fan-like shape, the fibers converging ventrally towards a small and flat coronoid process. The TS is medial to a large lacrimal gland, which fills most of the temporal fossa. The lateral surface of the TS is covered by a thin tendinous layer. Ventrally, the TS inserts on the dorsomedial surface of the coronoid process via a large aponeurosis. The TS muscle fibers are oriented vertically in the anterior part of the muscle, and are more oblique posteriorly.

Temporalis superficialis pars zygomatica

The pars zygomatica of the TS (pz-TS; Fig. 10) is a small fleshy strip on the ventral margin of the TS.

Unlike the TS, the pz-TS originates on a small area limited to the ventral surface of the zygomatic process of the squamosal (Fig. 10). Its obliquely oriented fibers insert on the dorsolateral surface of the mandibular notch. While the insertion area and orientation of the fibers are distinct from the anterior part of the TS, both muscles become harder to separate posteriorly, almost anastomosing at mid-lenght.

Temporalis profundus pars lateralis

The temporalis profundus (TP; Fig. 5B and10) is divided into two distinct parts. The pars lateralis (pl-TP) is a small fleshy block deep to the larger TS. The pl-TP takes its origin from the crest/orbital process formed between the anteroventral border of the temporal fossa and the groove for the ophthalmic vein and the oculomotor nerve (III). The pl-TP transversely widens from its origin to its insertion. Fiber orientation is similar to that of the anterior part of the TS, although they are slightly more oblique in coronal view.

The insertion of the pl-TP is short and extends from the mid-lenght of the mandibular notch to the anterior limit of the coronoid process. It covers most of the dorsal surface of the mandible in width. While the insertion is mostly muscular, the pl-TP shares the aponeurosis with the TS, anteriorly.

Temporalis profundus pars medialis

The temporalis profundus pars medialis (pm-TP; Fig. 5B and10) is the smallest part of the temporal muscle complex. It has no insertion, as it anastomoses with the pl-TP posterolaterally, but both parts could be easily separated during dissection. The fibers of the pm-TP are vertically oriented. Their insertion is medial to that of the pl-TP and extends from the level of the anterior tip of the pterygoideus externus pars inferior to the anterior margin of the optic foramen. The medialmost part of the pi-TP wraps the mandible medially, inserts on its dorsomadial surface and contacts the dorsal part of the mylohyoideus pars anterior (see 'Intermandibular musculature').

Pterygoid externus pars superior

The pars superior of the pterygoideus externus (ps-PE; Fig. 5b and10B) is a strap-like muscle that arises from an elongated fossa along the ventral limit of the temporal fossa. Its obliquely oriented fibers run posteriorly to wrap around the head of the articular condyle of the mandible, medially (Fig. 5B). The insertion extends from the anterior limit to the posterior tip of the blunt articular condyle. The ps-PE overlies the insertion of the pterygoideus externus pars inferior (see below).

Pterygoid externus pars inferior

Similarly to the ps-PE, the pterygoideus externus pars inferior (pi-PE; Fig. 5B) has a strap-like shape. In contrast with its upper counterpart, the pi-PE takes its origin on the pterygoid fossa. Specifically, the origin of the pi-PE is a small flattened area on the lateral surface of the palatal inflation. Its fibers are obliquely oriented and insert dorsally on the neck of the condylar process of the mandible.

Pterygoideus medius pars anterior

The pterygoideus medius (PM) is divided into two distinct parts that were easily separated during the classical dissection. The pars anterior (pa-PM; Fig. 5B and10C) takes its origin on the lateral and ventrolateral surfaces of the palatine inflation. The origin is muscular and spans from the caudal palatine foramen to an area just posterior to the origin of the pi-PE, near the posterior limit of the palatine inflation.

The fibers are more oblique anteriorly than posteriorly, and insert on the dorsal part of the pterygoid fossa of the mandibular ascending ramus. The posterior part of the pa-PM is thinner than its anterior part. The thick portion of the pa-PM serves as an attachment area for a small anterior projection of the pars posterior of the mylohyoideus (see 'Intermandibular musculature').

Pterygoideus medius pars posterior

The pars posterior of the pterygoideus medius (pp-PM; Fig. 5B and10B, C) consists of a fleshy block that takes its origin on an area located between the posterior part of the palatine inflation and the small fossa anterior to the pterygoid sinus. A coronal section shows that the fibers are obliquely oriented (Fig. S1D). The pp-PM presents a very small pars reflexa that extends from the anterior-to the posteriormost part of the pterygoid fossa of the ascending ramus, wrapping around the margin of the small angular process (Fig. 5B).

Facial-masticatory musculature

Buccinatorius pars externa

The pars externa of the buccinatorius muscle (pe-B; Fig. 10) is a thin sheet of obliquely oriented muscle fibers that envelops the pars interna of the buccinatorius. The muscle takes its narrow and anteroposteriorly elongated origin on the maxilla. Its posterior limit attaches just posteroventral to the zygomatic process of the maxilla. Its anterior part consists of a thin strap on the lateral surface of the maxilla, close to the lateral limit of the nasal cavity. The muscle wraps around the buccinatorius pars interna and reflects medially to insert along the dorsal part of the lateral surface of the mandible. Its insertion is shorter than its origin, extending from the level of the infraorbital foramen for the posterior two thirds of the length of the horizontal ramus.

Buccinatorius pars interna

The buccinatorius pars interna (pi-B; Fig. 10B) is an elongated and fleshy muscle that takes its origin just anteriorly to the coronoid process of the mandible. Posteriorly, the origin is laterally adjacent to that of the temporalis profundus pars medialis, at level of the optic foramen. It extends anteriorly to reach the level of the maxillary foramen. The orbital part of the pi-B is flattened due to the presence of the large lacrimal gland, dorsally. Laterally, it is limited by the presence of the temporalis superficialis pars anterior. The muscle slightly broadens anteriorly with a thin projection of its dorsal part wrapping around the lateral border of the dentary pad, to project into the space between the upper and lowers jaws. The pi-B is enveloped by the pe-B, laterally. The muscle fibers are horizontally oriented and extend until the level of the caudal nasal foramina. Anteriorly, the pi-B inserts on the ventral part of the lateral surface of the maxilla.

Mandibuloauricularis

The mandibuloauricularis (MA; Fig. 10) is a small fleshy muscle with a pseudocylindrical shape. It takes its origin on the anteroventral part of the auricular cartilage. The MA narrows ventrally towards its insertion on a small area of the posterodorsal margin of the angular process of the mandible, between the insertions of the masseter superficialis and the pterygoideus medius. The MA presents dorsoventrally directed fibers with a slight medial component.

Facial musculature

Dilator nasi

The dilator nasi (DN; Fig. 6C,D) is one of the five strap-like facial muscles in T. tetradactyla. The DN is thin and subtriangular in shape. It originates on the lateral surface of the maxilla with its ventralmost part reaching the level of the dorsal margin of the infraorbital foramen. The posterior margin of the DN is anteriorly inclined. The muscle narrows down anteriorly. The muscular part of the DN ends at about half the length of the rostrum and its fibers are horizontally oriented. The anterior end of the DN bifurcates. A long tendon inserts on the dorsal part of the nasal cartilage, anterior margin of the nasal bones. These tendons, as the remaining tendons of the facial muscles, were not visible in the contrast-enhanced scan.

Maxilolabialis superficialis pars superior

Similar to the DN, the maxilolabialis superficialis pars superior (ps-MLs; Fig. 6C) is a thin strap-like muscle. It is thinnest at the origin, which is slightly posterior to the origin of the DN. It is dorsoventrally short, stretching between the dorsal and the ventral lacrimal foramina. Therefore, the ps-MLs is narrower than most of the other facial muscles, with the exception of the maxilolabialis profundus pars superior (see below). Yet, it covers much of the ventral part of the DN. The muscular part of the ps-MLs narrows anteriorly from around a third of the rostrum length and reaches the tendinous part just posterior to the level of the foramina for the caudal nasal nerves [START_REF] Evans | Miller's Anatomy of the Dog[END_REF]. The long tendon attaches slightly obliquely oriented fibers of the ps-MLs to their insertion point on the upper lip, just dorsally to the labial commissure.

Maxilolabialis profundus pars inferior

The pars inferior of the maxilolabialis profundus (pi-MLp; Fig. 6D) is narrower than, but about the same length, as its superior counterpart. It takes its origin along the anteroventral part of the suture between the maxilla and the lacrimal (Fig. 6D). Posteriorly, it reaches the level of the lacrimal foramen, just anterior to the attachment of the jugal bone. Its fibers run horizontally, the muscular body stretching anteriorly from the origin. The tendinous part of the pi-MLp arises slightly anterior to the mid-lenght of the rostrum and inserts on the lower lip, ventrally to the labial commissure.

Maxilolabialis profundus pars superior

The maxilolabialis profundus pars superior (ps-MLp; Fig. 6D) is almost completely covered by the ps-MLs and the pi-MLp. The latter overlies its posteroventral part, while the former covers it anterodorsally.

The ps-MLp is the narrowest of the anterior facial muscles. Its small origin area is located ventrally to that of the DN, and posteriorly reaches the ventral margin of the infraorbital foramen (Fig. 6D). The tape-like muscle thickens from its origin area to the posterior half of its length. It becomes thinner and narrower anteriorly, with its horizontally oriented fibers inserting on a tendon connecting the nasal cartilage (Fig. 6D). The tendon is almost as long as its muscular counterpart.

Maxilolabialis superficialis pars inferior

The maxilolabialis superficialis pars inferior (pi-MLs; Fig. 6C) is the longest of the facial muscles. It has a triangular shape and overlies almost completely the pi-ML. The upper margin of the pi-MLs is adjacent to the ps-MLs, and is therefore equally slanted ventrally. Ventrally, the pi-MLs fibers cover the origin of the buccinatorius internus (see 'Facial-masticatory muscles'). Anteriorly, the muscular body of the pi-MLs bifurcates, with the dorsal and ventral branches attaching to tendons with slightly different orientations. These tendons were not completely preserved on the specimen, but appear to insert ventrally on the lower lip.

Intermandibular musculature

Intermandibularis anterior

The intermandibularis anterior (IA; Fig. 11; mylohyoideus pars anterior sensu Naples (1999b)) is a sheetlike muscle that arises from the symphysial cartilage. As the name indicates, the fibers are transversely oriented. They insert on both hemimandibles, covering the base of the tongue and the tendon of the geniohyoideus (see 'Intermandibular musculature') in ventral view. The IA is, therefore, a non-bilaterally symmetric muscle (Fig. S1E). It wraps around the ventral margin of the mandible to insert just dorsally to it, on the lateral surface. The IA extends posteriorly for slightly more than half the length of the horizontal ramus of the mandible. Posteriorly, it is adjacent with the anterior margin of the mylohyoideus pars anterior.

Mylohyoideus pars anterior

The pars anterior of the mylohyoideus (pa-Mh; Fig. 11) is a sheet-like muscle with transversely oriented, and covers the base of the tongue and the long tendon of the geniohyoideus (see below). Its morphological similarities with the intermandibularis anterior took previous studies to describe the latter as a distinct part of the mylohyoideus complex (Naples, 1999). In contrast to the intermandibularis anterior, the pa-Mh insertion takes its origin on ventral part of the medial surface of the mandible, between the widest point of the dentary pad and the pterygoid fossa posteriorly (Fig. 11). In addition to a different insertion, the pa-Mh is a bilaterally symmetric element, with both counterparts united medially by a small layer of conjunctive tissue. The pa-Mh is slightly thicker than the intermandibularis anterior. Posteriorly, the pa-Mh anastomoses with the mylohyoideus pars posterior, the two parts being continuous. In coronal view, the division between the two muscles is characterized by the passage of the sublingual artery [START_REF] Evans | Miller's Anatomy of the Dog[END_REF], ventral to the pterygoideus medius pars anterior (Fig. S1F).

Mylohyoideus pars posterior

The pars posterior of the mylohyoideus (pp-Mh; Fig. 11) is broader than pa-Mh. At the level of the orbital fissure, sublingual artery [START_REF] Evans | Miller's Anatomy of the Dog[END_REF] splits the insertions of the pa-Mh and the pp-Mh.

While the pa-Mh inserts on the mandibular ramus, the insertion of the pp-Mh extends along the medial surface of the palatine inflation, then along the ventromedial surface of the pterygoid sinus to continue posteriorly until the rostral tympanic process of the petrosal (Fig. 11). Additionally, a thin muscular projection inserts on the medial surface of the pterygoideus medius pars anterior. Posterior to the hard palate, the pp-Mh inserts on the soft palate, keeping its shape until it reaches the anterior part of the stylopharingeus, where it bifurcates. A fleshy fiber extension projects posteriorly to attach on a small area of the anterior surface of the stylohyal, just dorsal to its suture with the epihyal. On the other hand, a ventral sheet-like projection attaches to the tendon of the interstylohyoideus. As in other cases, the tendon could not be segmented. Nevertheless, the presence of muscular fibers of the interstylohyoideus confirm the position of the insertion of the pp-Mh described in previous studies (Reiss, 1997).

Hyoid, thyroid, and cricoid musculature

Geniohyoideus

The geniohyoideus (Gh, Figs. 11 and12) consists of a very long bilaterally symmetric element. Anteriorly, the Gh takes its origin on the ligament of the mandibular symphysis (Naples, 1999). Although the tendon is not visible in the contrast-enhanced scan, its origin can be traced by the empty gap, between the base of the tongue (dorsally) and the transversus mandibularis, pa-Mh, and pp-Mh (ventrally). This midline tendinous part of the Gh ends at the level of the zygomatic process of the squamosal, where the muscular fibers appear (Fig. 11). The fibers are horizontally oriented and grouped in two bilateral structures.

Nevertheless, both bellies appear to anastomose in the anterior half of the muscle. The Gh is overlain by the pp-Mh until near the interstyloideus ligament. The Gh inserts on the ventral surface of the fused ceratohyal and basihyal.

Interstylohyoideus

This muscle (ISh; Fig. 11) consists of a very thin sheet of transversely oriented fibers that take their origin along the anteroventral margin of the stylohyal. Its origin is located on the middle section of the stylohyal, and extends for roughly a third of its length. Ventrally, the muscular part of the ISh converges to a narrow tendon that wraps around the Gh and connects both bilateral elements. This tendon is the most posteroventral origin of the pp-Mh.

Mastostyloideus

The mastostyloideus (Mst; Fig. 12A-C) is a strap-like element that arises from the ventral part of a tiny vertically oriented gutter, which originates posteriorly to the stylomastoid foramen. The horizontally oriented fibers form a relatively thick bundle that inserts on the anterior tip of the stylohyal. This muscle is overlain by the sternomastoideus and borders the splenius capitis medially.

Ceratohyoideus

The ceratohyoideus (CeH; Fig. 12D-F) is triangular in shape and its obliquely oriented fibers are organized in a sheet-like element that takes its origin on the lateral surface of the epihyal bone. The origin stretches along the middle section of the bone. The CeH attaches on the thyrohyal from the ventrolateral margin of the anterior process, and extends towards the posterior process without reaching it. Ventrally, the CeH inserts along the slightly concave anterolateral surface of the thyrohyal, ending just dorsally to the fused suture with the ceratohyal.

Thyrohyoideus

The thyrohyoideus (ThH; Fig. 12D,E) is sheet-like, as other muscles lateral to the thyroid cartilage. It is subquadrangular in shape and its origin is dorsoventrally elongated, extending from just ventrally to the anterior process of the thyroid cartilage to the most ventral part of its lateral surface. Its ventral part wraps around the lateral aspect of the thyroid, presenting a small pars reflexa (Fig. 12E). Posteroventrally, its origin is adjacent with the insertion of the sternohyoideus (see 'Sternum musculature'). The ThH insertion area is thin and as elongated as its origin one. It extends from just ventrally to the insertion of the CeH all the way ventrally to the posterior margin of the ceratohyal.

Cricothyroideus pars recta

The cricothyroideus pars recta (pr-CTh; Fig. 12D,E) is the most lateral parts of this muscle. It consists of a relatively thick muscle strap, which takes its origin from the most anterior part of the ventral and ventrolateral surfaces of the thyroid cartilage. Ventrally, the pr-CTh presents a pars reflexa that connects the anterior margin of the cricoid cartilage to the posterolateral surface of the thyroid. The posterior part of the pars reflexa wraps around the small protuberance on the lateral aspect of the cricoid; its muscles fibers insert anteriorly on the posterodorsal part of the lateral surface of the thyroid. If the contrast does not allow to characterize the orientation of the muscle fibers of the pr-CTh, they were obliquely oriented, despite its name.

Cricothyroideus pars obliqua

The pars obliqua of the cricothyroideus (po-CTh; Fig. 12D,E) is placed medially to the pars recta. It presents a similar size to its lateral counterpart, which covers a small part of its anteroventral surface. The po-CTh takes its origin on the posterolateral surface of the cricoid cartilage. Contrary to the pr-Cth, the medial component of the muscle presents a small pars reflexa posterior to the lateral protuberance of the cricoid. The obliquely oriented fibers attach the cricoid posterolateral surface to the posterior process of the thyroid. The insertion of the po-CTh is located just ventrally to the rounded dorsal edge of the thyroid, and extends from the ventral surface of the tubercle of the posterior process to the level of the arytenoid cartilage.

Cricoarytenoideus posterior

The cricoarytenoideus posterior (CaP; Fig. 12D,F) covers the dorsal part of the cricoid cartilage. This muscle is sheet-like, pseudorectangular in dorsal view, and elongated anteroposteriorly. Its horizontally oriented fibers [START_REF] Diogo | Head and neck muscle evolution from sarcopterygian fishes to tetrapods, with a special focus on mammals[END_REF] take their origin on the posterior edge of the cricoid cartilage and insert on the ventrolateral surface of the arytenoid cartilage. The muscle thickens mediolaterally, presenting a round lateral edge for most of its length. This round edge is not present near the origin or insertion. At the anterior limit of the lateral edge, the CaP is briefly connected to the dorsal part of the cricoarytenoideus lateralis by connective tissue.

Cricoarytenoideus lateralis

The cricoarytenoideus lateralis (CaL; Fig. 12F) is the smallest muscle of the hyoid complex. It is a fleshy elongated muscle that originates on the cricoid cartilage. The muscle is wider dorsally and thins down ventrally, where it attaches to the medial surface of the pr-CTh by connective tissue. The insertion on the arytenoid cartilage is located slightly anterior to its cricoid origin. Its insertion is tendinous and is not visible on the 3D reconstruction. Laterally to its insertion on the arytenoid cartilage, the CaL is attached to the thyroarytenoideus pars medialis.

Thyroarytenoideus pars lateralis

The thyroarytenoideus pars lateralis (pl-ThA; Fig. 12F) is the largest part of the biggest muscle of the hyoid-related cartilaginous complex. In lateral view, this muscle is oval-shaped and takes its origin on a very shallow anteroposterior groove on the medial surface of the ventral part of the thyroid cartilage. Its origin is limited to the deepest part of the thyroid concavity, posteriorly. The fibers are vertically oriented.

The muscle is thick anteriorly, and thinner posteriorly. Its cross-section is medially concave, following the shape the thyroid cartilage that constitutes its lateral border. Medially, the pl-ThA is tightly bound to the pars medialis. Dorsally, the fibers converge towards its insertion area on the most lateral part of the arytenoid cartilage. The small tendinous part of the insertion is not visible on the 3D reconstruction.

Thyroarytenoideus pars medialis

The pars medialis of the thyroarytenoideus (pm-ThA; Fig. 12F) is much less voluminous than the pl-ThA.

Both parts anastomose ventrally and share a common origin. The pm-ThA and pl-ThA are similar in morphology. The CaL bounds to the posterodorsal margin of pm-ThA.

Pharynx musculature

Levator veli palatini

The levator veli palatini (l-VP; Fig. 12) is a small strap arising from the ventrolateral surface of the secondary hard palate formed by the medial pterygoid processes. The origin is narrow and extends from a medioventral point of the foramen of the auditory tube to the posteriormost margin of the pterygoid process. In cross-section, the most posterior part of the l-VP forms a separate flatter unit compared to the posterior fleshy block (Fig. S2A). The fibers of the posteromedial part of the l-VP were not well-stained, hindering the complete delineation of the two unit. They appear to eventually anastomose posteriorly. The fibers run posteroventrally, with a small medial angle, to insert on the soft palate. The posterior part of the l-VPs thins down and assumes a pointy shape. Bilaterally symmetric l-VPs flank the anterior tip of the medialis veli palatini (Fig. 12); they attach to the latter and to each other via a layer of connective tissue.

Medialis veli palatini

The medial element of the veli palatini (m-VP; Fig. 12) consists of the long fleshy and dorsoventrally compressed medial axis of the soft palate. Its anteroposteriorly oriented fibers arise from the soft palate, medial to the two l-VPs. The putative ligament connecting the muscle to the pterygoid shelves (Reiss, 1997) were not visible in the contrast-enhanced scan. The m-VP widens posteriorly to the origin and then gradually narrows down in the direction of the hyoid-thyroid complex (Fig. 12E,F). At its posterior end, the m-VP bifurcates into two thin straps that run medially to the stylopharyngeus and contrictores pharyngeus (see below), and then migrate dorsally to finally insert on the dorsal part of the pharynx (Fig. 13).

Stylopharyngeus

The stylopharyngeus (Sph;

Constrictores pharyngeus

The constrictores pharyngeus (CP; Fig. 12A-C and 13) is a complex of muscles composed by three different parts (e.g., [START_REF] Diogo | Muscles of vertebrates: comparative anatomy, evolution, homologies and development[END_REF]: constrictor pharyngis superior (anterior; CPa), constrictor pharyngis medius (median; CPm), and constrictor pharyngis inferior (posterior; CPp). Because the contrast-enhanced scan did not allow to recognize individual fibers (mainly in the median and posterior parts), these three parts could not be discretize. For simplicity sake, we refer to each part based on the external shape of the muscle, its origins/insertions, and its topology. The CPa is the longest part of the CP, it is easily identifiable by its tape-like shape (Fig. 13A-C and 13). It,takes its origin on the tuberosity medial to the auditory tube. Although the anteriormost part of the CPa was not visible in the contrastenhanced scan, its attachment to the ventrolateral surface of the splenius capitis muscle suggests a similar relative position of both muscles' origins. The muscle runs posteriorly, being enclosed between the ventral surface of the splenius capitis and the dorsal margin of the milohyoideus pars posterior (pp-Mh). At the length of the epihyal-stylohyal suture, the CPa lies as a thin layer between the splenius capitis and the Sph. At this level, the muscle fibers shift from a longitudinal to a transverse orientation. The transversely oriented fibers of the CPm arise from the most apical part of the posterior margin of the epihyal and from the dorsal surface of the thyrohyal (Fig. 12A). The CPm merges medially with its bilateral counterpart. It overlies the posterior part of the Sph laterally and dorsally (Fig. 12A andS1B). The posterior part of the CP complex arises from the dorsal surface of the thyroid cartilage. In dorsal view, the CPp covers the anterior part of the cricoarytenoideus posterior (Fig. 12C). At the posterior end, a well distinguishable muscle arises from the dorsomedial edge of the cricoid cartilage (Fig. 12C). This represents the pars cricopharingea of the CPp [START_REF] Saban | Musculature de la tête[END_REF][START_REF] Diogo | Head and neck muscle evolution from sarcopterygian fishes to tetrapods, with a special focus on mammals[END_REF].

Sternum musculature

Sternomandibularis

The sternomandibularis (Sm; Fig. 13A,C) is an anteroposterioly elongated muscle that takes its origin on the anterior surface of the lateral protuberance of the manubrium, just anterior to the articulation of the first rib. This muscle is tape-like in shape and passes ventrolaterally to the hyoid apparatus and pharynx.

Its anterior half is thinner than the posterior one. Anterior to the atlas, the Sm becomes narrower. Its insertion on the ventral edge of the horizontal ramus is relatively long, extending from the level of the sphenopalatine foramen to the dorsal margin of the infraorbital foramen.

Sternoglossus

The sternoglossus (Sg; Fig. 13) is extremely long. This muscle takes its origin on the cartilaginous extension in the posteriormost part of the sternum (xiphisternum). Near the origin, the muscle has a tapelike shape. It is bound to the sternal body segments until it reaches the manubrium, passing just dorsally to it. Anterior to the manubrium, the Sg thickens slightly. It binds to the hyoid complex, medially, and to the Sm laterally, by thick layers of the connective tissue. Between the manubrium and the cricoid cartilage, a large artery is imbedded in the Sg and follows its trajectory anteriorly. From this point, the Sg presents a circular cross-section. Anterior to the hyoid complex, it shifts to a midline position, meets its bilateral

Sternothyroideus

The sternothyroideus (Sth; Fig 13) takes its origin on the sternum, at the level of the second and third ribs.

This strap-like muscle remains attached to the sternum by connective tissue, projecting to the thyroid cartilage from the posterior margin of the manubrium. The Sth follows a parallel and adjacent trajectory to that of the Sg, until it inserts posterolaterally on the ventral margin of the thyroid cartilage, just ventral to the insertion of the pr-CTh.

Sternomastoideus

The sternomastoideus (SM; Fig. 13) is an elongated muscle that takes its origin from the anterior part of the manubrium. The origin is tendinous, small, and is located on the angle of the anterior flap-like projection of the manubrium, lateral to the jugular notch and just medial to the clavicular notch (Fig. 13C).

The muscular fibers are extremely long anteroposteriorly, and depart from the manubrium with an inclination of approximately 36°. The SM runs anterodorsally on the lateral side of the neck. With the exception of a few muscular fibers, the muscular part of the SM arises from its tendon anteriorly to the posterior cornu of the thyroid cartilage (Fig. 13A), around 20mm from the origin. The muscle broadens dorsoventrally giving the SM a strap-like shape. It also thickens mediolaterally, to a lesser extent. The SM becomes fleshy and runs in attachment with the lateral margin of the stylohyal bone. Anteriorly, it is tightly connected to the stylomastoideus muscle. The muscle fibers of the SM end near the tendinous insertion on a small groove just posterodorsally to the stylomastoid foramen.

Myrmecophaga tridactyla

Masticatory apparatus

Masseter superficialis

In M. tridactyla, the masseter superficialis (MS; Fig. 14) is a fleshy and anteroposteriorly elongated muscle. The MS originates from the ventrolateral margin of the zygomatic process of the maxilla. A strong tendon connects the origin to the almost horizontally oriented muscular fibers. The MS is thin at the origin, as it overlies the posterior part of the masseter profundus. It thickens posteriorly, as it extends anteriorly to the lacrimal foramen to the posterior limit of the masseteric fossa. The MS presents a pars reflexa throughout its full length. The pars reflexa wraps around the ventral edge of the mandible and becomes larger posteriorly, covering but the very posteroventral tip of the small angular process (Fig. 14A,C).

Masseter profundus

The masseter profundus (MP; Fig. 14B) takes its origin on the anterior part of the ventrolateral surface of the zygomatic arch. Its area of origin includes the small jugal bone and the posteroventral surface of the zygomatic process of the maxilla. The MP is in contact with the posterior part of the buccinatorius internus, medially (Fig. 14D). The MP is obliquely oriented; its inserts ventrally on the mandible and presents a small pars reflexa. The muscle is thick at its origin but thins down posteriorly, where it is overlain by the MS. The MP is half the length of the MS, with its insertion area stretching from the most posterior point of the lacrimal-maxilla suture to near the level of the coronoid process.

Temporalis superficialis

The temporalis superficialis (TS; Fig. 14) is a flat muscle covered almost entirely by the large lacrimal gland. It is a fan-like muscle arising from the temporal fossa extending from the level of the optic foramen to the root of the zygomatic process of the squamosal. The lateral surface of the TS is covered by a tendinous layer that thickens ventrally near the insertion of the muscle on the small coronoid process.

While the ventrally converging fiber of the TS reach the coronoid process posteriorly, the anterior part of the muscle inserts on the mandible uniquely via its tendinous layer (Fig. 14). The TS is well-separated from the pars zygomatica, posteriorly, due to the very distinct orientation of the muscular fibers.

Temporalis superficialis pars zygomatica

The pars zygomatica of the TS (pz-TS; Fig. 14) is the thickest part of the TS complex. It arises from the medial and posteroventral surfaces of the zygomatic process of the squamosal and extends anteroventrally with an oblique orientation. The pz-TS displays a medial portion that extends along the anterior margin of the neck of the mandibular articular process and inserts on the posterior surface of the blunt coronoid process. The lateral part of the pz-TS is larger and extends along the surface lateral to the mandibular notch. The ventralmost part of the pz-TS is slightly overlain by the dorsal margin of the MS. The pz-TS is easily distinguishable from its larger counterpart due to the different orientation angle of its fibers.

Temporalis profundus pars lateralis

The temporalis profundus (TP; Figs. 5C and14B, D) is divided into medial and lateral parts. The pars lateralis (pl-TP) is a blocky-shaped muscle arising from the ventral limit of the temporal fossa between the anterior tip of the orbital process and the insertion of the pars superior of the pterygoideus externus.

The posterior part of the pl-TP presents a quadrangular shape in lateral view, with the anterior part tapering in near the buccinatorius internus. The muscular fibers are dorsoventrally oriented with an oblique transversal component. The pl-TP inserts on the dorsal surface of the ascending ramus deep to the insertion of the TS. While the TP is well separated from the TS during the classical dissection, the incomplete staining of the former makes it sometimes hard to delimit. Anteriorly, the insertion of the pl-TP extends until the level of the anterior margin of the optic foramen (Fig. 5C).

Temporalis profundus pars medialis

The temporalis profundus pars medialis (pm-TP; Figs. 5C and 14B, C) in M. tridactyla is a medioventrally extending projection of the pl-TP. Both parts are anastomosed posteriorly, sharing the medial part of the TP origin. The pm-TP arises from the ventral surface of the orbital process lateral to the orbital fissure and the foramen rotundum. Slightly anterior to its origin, the pm-TP extends ventrally on the lateral surface of the ascending ramus (Fig. 5C). Anterior to this point, the two parts of the TP are distinguished by different insertion areas, with pm-TP reflecting medially. The insertion of the pm-TP is broad and extends

ventrally almost until the level of the mandibular canal. It is limited posteriorly by the mandibular canal.

The pm-TP tapers anteriorly to its contact with the posterior part of the buccinatorius internus at the orbit midlength. Fiber orientation in the pm-TP is similar to that of the pl-TP.

Pterygoideus externus pars superior

The pars superior of the pterygoideus externus (ps-PE; Figs. 5C and14B) is a broad and wide fleshy sheet muscle arising from the large fossa extending from the anteroventral part of the squamosal to the ventral part of the temporal fossa. Its fibers are obliquely oriented and extend posteroventrally to insert on the mandible just anteriorly to the jaw joint. The posteroventral part of the ps-PE is characterized by a large pars reflexa that wraps around the medial edge of the articular process. The pars reflexa of the ps-PE overlays the posterior part of the pars inferior of the PE.

Pterygoideus externus pars inferior

The pars inferior of the pterygoideus externus (pi-PE; Fig. 5C) is a strap-shaped muscle that originates from the anterior part of the pterygoid fossa, at the level of the optic foramen. In contrast with the ps-PE, the pi-PE is narrow and elongated. Its origin is thin, and lies medially to the pars interna of the temporalis profundus (pi-TP). The anterior part of the pi-PE is in tight contact with the pars anterior of the pterygoideus medius. The pi-PE slightly thickens up posteriorly, assuming a circular cross-section. The muscular fibers are horizontally oriented, with transversal oblique component as they insert posterolaterally on the anterior part of the neck of the articular process (Fig. 5C). The insertion of the pi-PE reaches about half the length of the neck and is overlain laterally by the pars reflexa of the ps-PE. The pi-PE merges with the pars reflexa of the ps-PE by a thick band of conjunctive tissue.

Pterygoideus medius pars anterior

The pars anterior (pa-PM; Figs. 5C and14C) is the larger of the two parts of the pterygoideus medius. It takes its origin from the small crest formed by the lateral edge of the palatine. In lateral view, the pa-PM presents a pseudorectangular shape. Anteriorly the muscle narrows down (Fig. 5C). The most anterior fibers originate just anteriorly to the level of the ethmoid foramen. The fibers extend ventrally to insert on a lateral prominence of the mandibular ascending ramus, ventrally to the passage of the inferior alveolar nerve and artery. Posteriorly, the fibers are dorsoventrally oriented, with an oblique transverse component.

Both origin and insertion of the pa-PM end roughly at the level of the palatine-pterygoid suture.

Pterygoideus medius pars posterior

The smallest component of the pterygoideus medius is a fleshy pseudorectangular band in lateral view (Fig. 5C). The origin of the pars posterior of the pterygoideus medius (pp-PM; Figs. 5C and14C) is very thin and extends from near the palatine-pterygoid suture to the pterygoid sinus at the level of the posterior limit of the jaw joint. The pp-PM is the continuation of the pa-PM until the tip of the angular process, where it reaches the insertion area of the auriculomandibularis. In lateral view, the fibers are vertically oriented, with a transversal component of about 21° relative to the sagittal axis of the skull. Posteriorly, the pa-PM becomes thicker but it tapers off abruptly at the level of the pterygoid sinus.

Facial-masticatory musculature

Buccinatorius pars externa

The pars externa of the buccinatorius (pe-B; Fig. 14) is an extremely sheet enveloping the much thicker pars interna (see below). The fibers of the pe-B have an oblique orientation, arising from the long and extremely narrow origin on the maxilla. The origin extends from the level of the most posterior mental foramen to the anterior edge of the zygomatic process of the maxilla. The pe-B extends ventrally, envelopes the pars interna and reflects medially. The muscle wraps around the ventromedial margin of the pars interna of the buccinatorius and projects dorsally to insert on the dorsolateral surface of the mandibular horizontal ramus. Its insertion and origin areas are similar in length, but the bad preservation of the soft tissues in the snout did not permit to clearly observe of the anterior tip of its origin.

Buccinatorius pars interna

The pars interna of the buccinatorius (pi-B; Fig. 14B) is extremely long anteroposteriorly, reflecting the elongation of the rostrum. The muscle takes its origin on the maxilla, adjacent to the labial commissure of the mouth. Its fibers go on to insert on the dorsal surface of the horizontal ramus of the mandible, ventrally to the eye and the lacrimal gland. The fibers have an almost horizontal orientation, leaning slightly ventrally. In cross section, the anterior part of the pi-B is dorsoventrally elongated, showing a small ventromedial projection. The most anterior part of the pi-B presents a medial flap-like projection that rests between both jaws (Figs. 14B andS2). At the length of the anterior most tip of the nasal, the pi-B drifts ventrally and narrows dorsoventrally (Fig. 14C). Posteriorly to the zygomatic process of the maxilla, the pi-B leans medially to a position between the jaws, deep to the masseter superficialis (MS). This marks the beginning of the insertion of the pi-B, which extends until the anterior part of the insertion of the temporalis profundus (TP), just anterior to the level of the optic foramen.

Mandibuloauricularis

The mandibuloauricularis (MA) consists of a small fiber bundle that takes its origin from the anterior part of the auricular cartilage. It inserts on the posterior tip of the angular process, between the pars posterior of both masseter superficialis (pp-MS) and pterygoideus medius (pp-PM). This muscle was damaged on the digitally dissected side of the skull and was described based on its right counterpart.

Facial musculature

Dilator nasi

The dilator nasi (DN; Fig. 6A,B) is an extremely thin sheet of horizontally oriented fibers. It is the most dorsal of the anterior facial muscles. It takes its origin on the dorsal part of the lateral surface of the maxilla, with the muscular fibers stretching anteriorly from the level of the most posterior point of the nasal to about mid-length of the rostrum The DN broadens slightly anteriorly to its origin and narrows down abruptly at its most anterior part, which attaches via a tendon. The length of the tendon more than doubles the length of the muscular portion of the DN. It runs for more than half of the rostrum length to insert on the nasal cartilage at the level of the nostrils.

Maxillolabialis superficialus pars superior

The maxillolabialis superficialis pars superficialis (ps-MLs; Fig. 6A) is the more anterior of the dorsal facial muscles. This thin and elongated muscle is broader at its posterior and median parts, thinning anteriorly. The ps-MLs is slightly thicker ventrally than dorsally. Its posterior and middle parts overlie the maxillolabialis profundus pars media and pars superior anteriorly. The ps-MLs and the DN are similar in length. A tendon, as long as its muscular counterpart, connects the ps-MLs to the upper lip.

Maxillolabialis superficialis pars inferior

The pars inferior of the maxillolabialis superficialis (pi-MLs; Fig. 6A) is the most posterior of the facial muscles described in this section. It arises from an area dorsal to the maxilla-frontal-lacrimal contact. Its anterior half covers the posterior parts of the pars media and pars superior of the maxillolabialis profundus. The muscle fibers reach just posterior to the most anterior point of the fronto-nasal sutures.

From this point, an extremely long tendon runs anteriorly to insert just posteroventrally to the buccal commissure. In M. tridactyla, the pi-MLs is dorsally placed when compared to the condition in T.

tetradactyla.

Maxillolabialis profundus pars inferior

The maxillolabialis profundus pars inferior (pi-MLp; Fig. 6B) takes its origin on the anterodorsal surface of the zygomatic arch of the maxilla. Its origin overlies the anterior part of the tendon of the masseter superficialis. The height of the posterior part of the pi-MLp contrasts with its extremely thin anterior part.

The anterior half of the muscle consists of an extremely thin bundle of a few horizontally oriented fibers.

The muscular part of the pi-MLp runs for slightly more than a third of the rostrum length. This muscle appears to insert on the pars anterior of the MLp, as an individual tendon was hard to identify during the classical dissection.

Maxillolabialis profundus pars anterior

The pars anterior of the maxillolabialis profundus (pa-MLp; Fig. 6A) is extremely thin compared to its posterior counterpart (pi-MLp). The pa-MLp overlies the anterior half of the pi-MLp. This muscle might correspond to an anterior extension of the pi-MLp. The anterior part of the pa-MLp flanks the ventral margin of the ps-MLs. The insertion of the pa-MLp just posteriorly to the buccal commissure is done through a tendon almost equivalent in length to its fibers.

Maxillolabialis profundus pars media

This part of the maxillolabialis profundus (pm-MLp; Fig. 6B) is a thin fiber bundle between the pars inferior and the pars superior of the MLp. The pm-MLp is the most dorsoventrally compressed of the dorsal facial muscles, with a length similar to that of the DN. Its origin is anterodorsal to that of the pars inferior of the MLp. As previously described, the anterior part of this muscle is covered by the ps-MLs.

The pm-MLp tendon appears to be fused with that of the pm-MLp and the pi-MLp, which is in line with previous observations (Naples, 1985a).

Maxillolabialis profundus pars superior

The maxillolabialis profundus pars superior (ps-MLp; Fig. 6B) is a more dorsal and broader replicate of the pm-MLp. The origin is just slightly anterior to that of the pm-MLp, and both muscles are similar in length. From classical dissection, this muscle appears to share a tendon with the ps-MLs, with both muscles sharing an insertion posterodorsally to the buccal commissure.

Intermandibular musculature

Intermandibularis anterior

The transversus mandibularis (IA; Fig. 15; mylohyoideus pars anterior sensu Naples, 1999a) is extremely elongated, extending for almost half the mandibular length (127.4 mm). This muscle is very thin and forms a sheet covering the tendon of the genioglossus as well as the tongue (not figured). Each fiber is attached to thin areas on the ventrolateral surfaces of both mandibles. The muscle wraps around the ventral margin of the mandible and the transversely oriented stretch to insert on the symmetric element. The fibers are continuous between mandibles.

Mylohyoideus pars anterior

The postcranial muscles in our specimen were not successfully stained by the iodine solution and, therefore, could not be illustrated and described (Fig. 15). The pars anterior of the mylohyoideus (pa-Mh;

Comparison

Masticatory apparatus, auxiliary facial muscles, and intermandibular musculature

The anatomy of the masticatory apparatus is similar in the three studied species of anteater (Figs. 4,[START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF][START_REF] Anthony | La dentition de l'oryct erope. Morphologie, d eveloppement, structure, interpr etation[END_REF]. However, the pterygoideus and masseter complexes present different number of elements between the Cyclopedidae and the Myrmecophagidae. While in M. tridactyla and T. tetradactyla the pterygoideus medius (PM) is divided into anterior (pa-PM) and posterior (pp-PM) parts, C. didactylus shows one single unit (Fig. 5) that could not be separated neither with digital or classical dissection. The PM of C. didactylus also differs from that of Myrmecophagidae in the more reduced anterior extension of its origin. In M. tridactyla and T. tetradactyla, the pa-PM origin on the palate extends anteriorly to the level of the optic foramen (Figs. 10C and 14C, while in C. didactylus it is slightly more posterior (Figs. 5 and7A). C.

didactylus also presents a very dense layer of connective tissue, which is located laterodorsally to the insertion of the PM on the mandible.

The mandibular musculature of C. didactylus can also be distinguished from that of the other anteaters by the presence of a dorsolaterally oriented mandibuloauricularis (MA). This is due to a more anterior position of the auricular cartilage in C. didactylus compared to myrmecophagids. The fossa for the external auditory meatus is anterodorsally elongated, with its anterior margin reaching the base of the zygomatic process of the squamosal (Fig. 4B). Another trait that distinguishes C. didactylus musculature is the absence of a masseter profundus. C. didactylus also lacks a jugal bone, which is the origin of the masseter profundus in myrmecophagids. The masseter superficialis muscle fibers are further posteroventrally from the upper jaw in C. didactylus compared to the myrmecophagids. Therefore, the masseter superficialis is attached to the upper jaw by a long tendon in C. didactylus (Fig. 4). Additionally to the lack of a masseter profundus, C. didactylus displays a bipartite masseter superficialis (Fig. 4), while it is composed by a single layer in myrmecophagids (Figs. 10 and 14). Volume wise, the masseter superficialis (MS) is much larger in T. tetradactyla and M. tridactyla (Table 1). These differences are reflected in the muscle shape, with the MS being thicker in the latter two than in C. didactylus.

The remaining differences between the masticatory apparatus of C. didactylus and myrmecophagids relates to muscle shape and proportions. The temporalis muscle complex is proportionally much larger in C. didactylus than in myrmecophagids (Table 1). The temporalis superficialis (TS) accounts for 42.2% of the total volume of the masticatory apparatus, while in T.

tetradactyla this proportion is reduced by half (20.9%) and to 13.5% in M. tridactyla (Table 1). In myrmecophagids, the TS is flatter and compressed by the large lacrimal gland (Figs. [START_REF] Thewissen | Evolutionary aspects of the development of teeth and baleen in the bowhead whale[END_REF][START_REF] Anthony | La dentition de l'oryct erope. Morphologie, d eveloppement, structure, interpr etation[END_REF]. Contrary to M. tridactyla and C. didactylus, the TS fibers are bipennated (Fig. S1B), their insertion on the coronoid process is muscular rather than aponeurotic. The temporalis profundus (TP) is relatively larger compared to its counterparts in M. tridactyla and T. tetradactyla. The pars lateralis (pl-TP) is twice as large in C.

didactylus (Table 1) and shows a higher origin in the temporal fossa (Figs. 4B, 10B, and 14B). The pars zygomatica of the temporalis superficialis (pz-TS) presents an inverse trend in volume percentage, being smaller in C. didactylus than in myrmecophagids (Table 1).

The volumes of the pterygoideus complex show a trend for an increase of the pars superior of the pterygoideus externus (ps-PE) with specimen size. Both pterygoideus externus pars inferior (pi-PE) and pterygoideus medius showed some differences in volume that do not appear to present any correlation with specimen size (Table 1).

Volume percentages in the facial-masticatory and transverse mandibular muscles show similar values in all three species. Anatomically, the muscles are very similar in all species, with the buccinatorius muscles (B) changing proportionately with rostrum elongation. This layer exhibits keratinous spicules with the apex oriented posteromedially.

The intermandibularis anterior is similar in all three species.

Hyoid, thyroid, and pharynx musculature

We report four main differences between T. tetradactyla and C. didactylus. pars inferior (pi-MLp) are present in all species (Fig. 6). In C. didactylus, the pi-MLp originates dorsally on the maxilla, just dorsal to the tendinous insertion of the masseter superficialis (MS). In myrmecophagids, the origin of the pi-MLp is located more ventrally (Fig. 6). The maxillolabialis profundus pars superior (ps-MLp) is also present in all species, with a second similar but smaller element present between the former and the pi-MLp. We name it maxillolabialis profundus pars media (pm-MLp;

see 'Results'). M. tridactyla presents a unique maxillolabialis profundus pars anterior (pa-MLp) that resembles an anterior extension of the pi-MLp (Fig. 6).

The superficial layer of the maxillolabialis complex is made up of one element in C. didactylus and two in T. tetradactyla and M. tridactyla (Fig. 6). The maxillolabialis superficialis pars superior (ps-MLs; Fig. 6) is topologically similar in T. tetradactyla and C. didactylus. It overlies, to some extent, the DN and the pi-MLp in both species, but also the pi-MLp in C. didactylus. Its origin is located over the maxilla-frontal-lacrimal intersection in C. didactylus, with the muscle fibers becoming more anterior in the largest species (Fig. 6). In M. tridactyla, the posterior fibers arise at the level of the anterior process of the frontal. The maxillolabialis superficialis pars inferior (pi-MLs) is only present in the myrmecophagids (Fig. 6). It forms a sheet that resembles the pi-MLp in T. tetradactyla, while its origin is more dorsal and only marginally overlies the pi-MLp in M. tridactyla (Fig. 6).

Discussion

Comparative myology in anteaters

The upper and lower jaws of anteaters represent a unique example of extreme skull elongation within mammals. Anteaters are completely toothless and have lost the ability to perform chewing movements (Naples, 1999). Despite this, as in most other mammals, their jaw mechanics is defined by a conserved number of homologous muscular elements [START_REF] Greaves | The mammalian jaw : a mechanical analysis[END_REF].

Our results mostly agree with previous descriptions of the muscular anatomy of anteaters (Owen, 1856;[START_REF] Windle | On the myology of the Edentata[END_REF]Naples, 1985aNaples, , 1999;;Reiss, 1997;Endo et al., 2007Endo et al., , 2017)), except for the recognition of the intermandibularis anterior muscle (IA). Naples (1999) considered this muscle as being a part of the mylohyoideus (ML). We showed that this muscle is attached to the ventrolateral margin of the anterior part of the lower jaws, which contrasts with the insertion area of the mylohyoideus.

Furthermore, we confirmed that the IA is made of transversally continuous fibers. The mylohyoideus pars posterior (pp-Mh) and pars anterior (pa-Mh) comprise two bilaterally symmetric muscles that join along a midline axis (Fig. S1C). A similar condition is found in anteaters' sister taxon, sloths (Naples, 1986), as well as in other mammals like moonrats [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF], nectarivorous bats [START_REF] Wille | Muscular adaptation of the nectar-eating bats (Subfamily Glossophaginae)[END_REF], and humans (Gray, 1995). [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF] uses two criteria to assign a digastricus pars anterior to the mylohyoideus:

i) the presence of intertonguing connection at the midline, and ii) the contiguity of the attachment on the mandible. None of these conditions was found in the "pars anterior of the mylohyoideus" (sensu Naples, 1999). Therefore, we propose to consider this muscle as the intermandibularis anterior [START_REF] Diogo | From fish to modern humans -comparative anatomy, homologies and evolution of the head and neck musculature[END_REF]. The mylohyoideus pars anterior (sensu Naples, 1999), the transversus mandibularis of rats [START_REF] Greene | Anatomy of the rat[END_REF] and the pars anterior of the mylohyoideus of tree-shrews (Le Gros Clark, 1924) are developmentally distinct from the true mylohyoideus, the former being homologous with the sarcopterygian intermandibularis anterior while the latter is homologous to the intermandibularis posterior [START_REF] Diogo | From fish to modern humans -comparative anatomy, homologies and evolution of the head and neck musculature[END_REF]. This muscle acts as a stabilizer of the mandibular symphysis [START_REF] Hautier | Masticatory muscle architecture in the Laotian rock rat Laonastes aenigmamus (Mammalia, Rodentia): new insights into the evolution of hystricognathy[END_REF]. It is found mostly in mammals in which this structure is especially mobile [START_REF] Hiiemae | The structure and function of the jaw muscles in the rat (Rattus norvegicus L.)[END_REF]).

In agreement with previous works (Naples, 1999;Endo et al., 2007Endo et al., , 2017)), we showed that the complexity of the masseter is reduced compared to the condition observed in other mammals (Naples, 1985b). We follow Naples (1999) in considering that C. didactylus presents a single masseter superficialis, divided in two parts. C. didactylus presents one single large tendon that connects the masseter musculature to the zygomatic process of the maxilla, with both parts presenting a pars reflexa. This suggests that the masseter muscle of C. didactylus is reduced to a superficial element. On the other hand, [START_REF] Endo | [END_REF][START_REF] Endo | [END_REF] divided the masseter musculature of T. tetradactyla and M. tridactyla in deep and superficial separate muscles. This would imply that the masseter profundus was lost in the cyclopedid lineage. In other mammals, the masseter profundus arises from the zygomatic arch [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF][START_REF] Cox | Reviewing the morphology of the jaw-closing musculature in squirrels, rats, and guinea pigs with contrast-enhanced microCT[END_REF]Fabre et al., 2017;Ginot et al., 2018), which is absent in C. didactylus. Such a loss could be linked to the absence of a masseter profundus, given that cartilage-bone development is partly dependent on embryonic muscular contractions (Hall & Herring, 1990;[START_REF] Atchley | A model for development and evolution of complex morphological structures[END_REF]Rot-Nikcevic et al., 2006;Zelditch et al., 2008). In contrast, jugal bones are present in T. tetradactyla and M. tridactyla, and associated with a separate masseter profundus, as observed in their sister taxon (i.e. sloths; Naples, 1985b).

The presence of two masseter muscles therefore represents the plesiomorphic condition for anteaters. The complete loss of a functional zygomatic arch and masseter profundus in C. didactylus offers a striking example of developmental integration linked to muscle bone interaction, as well as an empirical evidence of modularity within the masticatory apparatus.

Despite the presence of a jugal bone in Tamandua and Myrmecophaga, all anteaters putatively lack a zygomaticomandibularis muscle (Edgeworth, 1923;Naples, 1999). However, we found a wellseparated pars zygomatica of the temporalis superficialis in the three species of anteaters, especially in C.

didactylus. Naples (1985b) proposed that the temporalis superficialis of Choloepus spp. (two-toed sloths) presented a pars zygomatica. Naples (1999) homologized the posterolateral part of the temporalis superficialis of M. tridactyla with the pars zygomatica of Choloepus. Contrary to the temporalis superficialis pars zygomatica in the two-toed sloths (Naples, 1999), we showed that the pars zygomatica does not insert on the anterior edge of the coronoid process, in anteaters. Instead, it inserts on along the medial part of the mandibular notch (Figs. 1B, 4, 10, 14). [START_REF] Edgeworth | On the development and hyoid of the mandibular and hyoid muscles of mammals[END_REF] argues that the zygomaticomandibularis (sensu [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF] separates from the temporal during the development of Dasyurus spp. (quolls), which might be equally the case in other mammals [START_REF] Druzinsky | Mammalian masticatory muscles: homology, nomenclature, and diversification[END_REF].

According to [START_REF] Druzinsky | Mammalian masticatory muscles: homology, nomenclature, and diversification[END_REF], the zygomaticomandibularis is not separable from either the masseter or the temporalis complexes in some carnivores, ungulates, bats, and marsupials. We argue that the temporalis superficialis pars zygomatica of anteaters is not homologous to that of Choloepus spp. (Naples, 1985b) and other xenarthrans (Edgeworth, 1923), but instead might be related to the "zygomaticomandibularis posterior" [START_REF] Druzinsky | Mammalian masticatory muscles: homology, nomenclature, and diversification[END_REF]Fabre et al., 2017). This homology is retained here as a working hypothesis. We propose that the name of the temporalis superficialis pars zygomatica should not be changed until further evidence is collected from embryological data.

Functionally, we found evidence for a shift between C. didactylus and the myrmecophagid anteaters. The temporal musculature appears to play a much more relevant role in mandibular movements in C. didactylus (42.2%) than in larger anteaters (13.5-20.9%). On the other hand, both myrmecophagids present a masseter musculature accounting for about a third of the total volume, while it is three times smaller in C. didactylus. While this may relate directly with the loss of a true deep masseter, it also implies a change in the position and orientation of the main vector of force contributing for mandibular elevation [START_REF] Hylander | Functional anatomy and biomechanics of the masticatory apparatus. Temporomandibular Disorders: An Evidenced Based Approach to Diagnosis and Treatment[END_REF][START_REF] Greaves | The mammalian jaw : a mechanical analysis[END_REF]. The masseter superficialis generates anterodorsally directed forces [START_REF] Barbenel | The biomechanics of the temporomandibular joint: a theoretical study[END_REF][START_REF] Baron | A biomechanical functional analysis of the masticatory muscles in man[END_REF]Fabre et al., 2017). On the other hand, the temporalis complex generates forces with vertical to posterodorsal directions (e.g., [START_REF] Barbenel | The biomechanics of the temporomandibular joint: a theoretical study[END_REF][START_REF] Baron | A biomechanical functional analysis of the masticatory muscles in man[END_REF].

This is due to its subdivisions (two to four) that contribute with differently oriented force vectors (e.g., [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF][START_REF] Otten | Concepts and models of functional architecture in skeletal muscle[END_REF]. Naples (1999) suggested that the masseter and temporalis musculature plays a role in depressing the medial and ventral edges of the mandible in M. tridactyla. The temporalis generates a medial rotation of the dorsal edge of the ascending ramus of the mandible, while the masseter contributes to the rotation of its ventral margin (Naples, 1999). As a result, the anteroventral part of the mandibular body depresses while the unfused mandibular symphysis cartilage stretches during tongue protrusion.

We showed that the masticatory apparatus of T. tetradactyla is very similar to that of M. tridactyla and therefore support [START_REF] Endo | [END_REF] view that mandibular movement is probably similar in both species.

The musculature of the masticatory apparatus of C. didactylus differs not only in terms of proportions and number of masseter elements, but also at the level of the fiber architecture, with its temporalis superficialis exhibiting a bipennate arrangement of oblique fibers (Fig. S1B). Bipennate and multipennate muscles generate larger forces (increased physiological cross-section areas) than unipennate muscles or muscles with parallel fiber arrangement [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF][START_REF] Gans | Functional bases of fiber length and angulation in muscle[END_REF][START_REF] Hylander | Functional anatomy and biomechanics of the masticatory apparatus. Temporomandibular Disorders: An Evidenced Based Approach to Diagnosis and Treatment[END_REF]). This appears to correlate with the relatively more developed ascending ramus of the mandible, particularly the coronoid process. Although the initiation of the coronoid development is an intrinsic process to the mandibular ossification, its growth is dependent on muscle-bone interaction (Anthwal, Peters, & Tucker, 2015). As discussed previously, the absence of jugal bone is probably related the extremely reduced masseter musculature. A similar condition is found in the tailless tenrec (Tenrec ecaudatus; [START_REF] Oron | A cineradiographic and electromyographic study of mastication inTenrec ecaudatus[END_REF]. As in C. didactylus, tailless tenrecs have lost the jugal bones and the masseter profundus, displaying a relatively small masseter superficialis with a tendinous insertion on the zygomatic process of the maxilla [START_REF] Oron | A cineradiographic and electromyographic study of mastication inTenrec ecaudatus[END_REF]. Their temporalis musculature, on the other side, makes up for most of the adductor muscles' volume [START_REF] Oron | A cineradiographic and electromyographic study of mastication inTenrec ecaudatus[END_REF].

Despite the differences between C. didactylus and myrmecophagids, all anteaters present many similarities regarding their adaptations to ant-and termite-eating: an unfused mandibular symphysis, the presence of an intermandibularis anterior, a well-developed mylohyoideus muscle, an extremely long sternoglossus, and the absence of a digastricus muscle. This suggests that mouth opening during tongue protrusion in C. didactylus might be similar to that of T. tetradactyla and M. tridactyla. The orientation of the ascending ramus and the coronoid process supports this view. Contrary to other mammals (e.g., [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF], C. didactylus presents laterally oriented coronoid processes (Figs. 4B,5A). Then, the contraction of the temporalis superficialis pulls the coronoid process medially, causing the ventral margin of the mandibular body to rotate laterally. The larger forces generated by the temporalis complex and the shorter horizontal body of the mandible in C. didactylus compared to myrmecophagids, might result in very similar mandibular movements and global momentum to those in myrmecophagids, despite the reduction of the temporalis muscle in the latter. As in anteaters, the mandibular symphysis of the tailless tenrecs is highly mobile, allowing a high degree of movement around the longitudinal axis of the mandible [START_REF] Mills | The functional occlusion of the teeth of Insectivora[END_REF][START_REF] Oron | A cineradiographic and electromyographic study of mastication inTenrec ecaudatus[END_REF]. [START_REF] Oron | A cineradiographic and electromyographic study of mastication inTenrec ecaudatus[END_REF] suggested that the loss of the masseter profundus and the reduced complexity of molars facilitate the mediolateral rotation of the mandible during occlusion. The morphological similarities between C. didactylus and T. ecaudatus suggest that similar mediolateral rotation of the jaws is possible despite a shift in force distribution during the chewing cycle.

In addition to anteaters and tenrecs, mandibular mediolateral rotation plays a key role in mysticetes (Marshall, 2009;Pyenson et al., 2012). The innervation patterns of the toothless dorsal margin of the mandible in anteaters and baleen whales, and its sensorial role in the coordination between mandibular movements and tongue protrusion/gulping (anteaters and baleen whales respectively) was previously discussed (Peredo et al., 2017;Ferreira-Cardoso et al., 2019). Assuming this link, the presence of similar patterns of dorsal canaliculi in C. didactylus and myrmecophagids is an additional evidence of similar mandibular movements. However, this will have to be demonstrated by applying biomechanical models to the masticatory apparatus of all three anteater genera.

Similar function in morphologically distinct masticatory apparatus makes extant anteaters an example of many-to-one-mapping of form to function (Wainwright et al., 2005;[START_REF] Strobbe | Survival selection on escape performance and its underlying phenotypic traits: a case of many-to-one mapping[END_REF].

Extant anteaters lineages diverged during the late Eocene (≈37.8 Mya, Gibb et al., 2016) with the earliest fossil dating back from the Late Oligocene to the Early Miocene (≈23.0 Mya; [START_REF] Carlini | Un singular Myrmecophagidae (Xenarthra, Vermilingua) de Edad Colhuehuapense (Oligoceno tardío-Mioceno temprano) de Patagonia, Argentina[END_REF].

Currently, it is not known if their most recent common ancestor was toothless and myrmecophagous.

Nevertheless, Meredith et al. (2009) showed that the enamelin gene (ENAM) was already non-functional (pseudogene) in the common ancestor of Pilosa (anteater and sloths). Furthermore, their ancestral state reconstruction indicated that the common ancestor to the Vermilingua was probably toothless. In this scenario, strict myrmecophagy is plesiomorphic to this clade, with associated functional adaptation and changes to the masticatory apparatus occurring differently under in the two extant lineages (Cyclopedidae and Myrmecophagidae).

Endo (2017) described a vestigial "digastricus posterior" in T. tetradactyla, but probably referred to the mandibuloauricularis, as no connections were found with the hyoid apparatus. We did not find a digastricus pars posterior neither during the classical nor the virtual dissections, confirming observations by Naples (1999). Contrary to previous publications (Naples, 1985a;Reiss, 1997) we identified a pars externa of the buccinatorius in C. didactylus. Our observations of the buccinatorius (pars interna and externa) confirmed the importance of this muscle in the feeding apparatus of all extant anteaters. Naples (1999) highlighted the role of this muscle in contributing to the removal of attached ants during tongue protrusion.

Comparison with the myology of pangolins

Pangolins are often referred to as scaly-anteaters and are a well-known example of ecological and morphological convergence with anteaters (McGhee, 2001;[START_REF] Rose | Xenarthra and Pholidota[END_REF]. However, pangolins present several muscular differences with anteaters in their skull. First, the masseter muscle appears to be more complex than in anteaters, with three parts described in Manis javanica (Sunda pangolin; [START_REF] Endo | [END_REF]. In contrast, [START_REF] Windle | On the myology of the Edentata[END_REF] reported that the masseter is thin and "unilaminar" in Manis spp., taking its origin on a "fibrous zygoma". Three muscle bundles are visible in Endo et al. (1998;Fig. 7), the anterior two putatively originating on the zygomatic process of the maxilla, while the posterior one originates from the zygomatic arch. The areas of origin of the masseter are not illustrated and differences in fiber orientation are not provided (Endo et al., 1998), although the most anterior bundle appears to be the most vertically oriented (Fig. 7; Endo et al., 1998). This might suggest the existence of a masseter superficialis with two parts, as in C. didactylus, with a small masseter profundus anteriorly.

However, the origins reported by Endo and colleagues (1998) do not correspond to such divisions (e.g., [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF]. Edgeworth (1923) describes the masseter as arising from the "lower margin of the zygomatic portion of the superior maxilla", while a more oblique muscle arises from the medial surface of the zygomatic arch ("zygomaticomandibularis"). The figures associated to Edgeworth's (1923;Figs. 59 and 60) suggest that the author's zygomaticomandibularis could also be a masseter profundus. It is not possible, with the available information, to establish clear homologies with the masseter of anteaters.

However, previous reports suggested that the masseter of pangolins is multi-layered (contra [START_REF] Windle | On the myology of the Edentata[END_REF], possibly composed of two separate parts as in T. tetradactyla and M. tridactyla.

Furthermore, if pangolins have a "true" zygomaticomandibularis, this muscle is not homologous to the putative zygomaticomandibularis of anteaters as discussed above.

Second, the pterygoideus complex of pangolins is composed of a pterygoideus externus, and a pterygotympanicus (Edgeworth, 1923;Endo et al., 1998). Edgeworth (1923) described a pterygoideus medius that is atrophied during development, with a medial pterygo-hyoideus connecting to the epihyalstylohyal bones. Yeh (1984) and Endo et al. (1998) reported the absence of pterygoideus medius. An accurate description of the pterygo-hyoideus in the adult pangolin was not provided. As for the pterygoideus externus, Endo et al. (1998) suggested the presence of two muscles bundles, but did not consider this muscle to be divided in two parts, as in anteaters. It appears that the pterygoideus externus of pangolins corresponds to the pars inferior of the muscle in anteaters, as it arises from the pterygoid bone (Edgeworth, 1923). In anteaters the pars superior of the pterygoideus externus arises from the parietal bone, just ventrally to the temporal fossa. Lastly, pangolins present a muscle not found in anteaters: the pterygotympanicus (Edgeworth, 1923) that takes its origin on the ventral part of the alisphenoid bone and inserts on the tympanic bulla. A posteromedial projection of this muscle gives rise to the tensor veli palatini, a muscle that we found exclusively in C. didactylus.

Unlike anteaters, pangolins appear to present a digastricus (Endo et al., 1998). It is, nevertheless, less developed than in other mammals (e.g., [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF]. Endo et al. (1998) described two parts of the digastric, with the lateral part corresponding to what is commonly known as the "posterior belly".

Windle and Parsons (1899) also described a digastricus in pangolins, although not dividing it into two distinct parts. Edgeworth (1923) homologized the digastricus of [START_REF] Windle | On the myology of the Edentata[END_REF] to the mandibuloauricularis.

In pangolins, the tongue musculature is composed of a sternoglossus (fusion of the hyoglossus with the sternohyoideus) reaching an extremely long xiphoid cartilage at the posterior end of the sternum [START_REF] Macalister | Report on the anatomy of insectivorous Edentates[END_REF][START_REF] Jentink | Revision of the Manidae in the Leyden Museum[END_REF]Edgeworth, 1923). This condition is similar to that found in anteaters, although the xiphoid cartilage is relatively much longer in pangolins [START_REF] Doran | The tongue and associated structures in two species of African pangolins, Manis gigantea and Manis tricuspis[END_REF]. Unlike in anteaters, the sternohyoideus does not contribute to the posterior part of the sternomandibularis, and this muscle appears to be completely absent [START_REF] Windle | On the myology of the Edentata[END_REF]Edgeworth, 1923;Endo et al., 1998). The geniohyoideus fuses with its bilateral counterpart into a medial band, then presenting two lateral bands posteriorly, as in anteaters.

Also, in pangolins, both intermandibularis anterior and posterior have been described (Edgeworth, 1923). However, both present a medial raphe, which suggests that these elements are homologous to the mylohyoideus pars anterior and posterior of anteaters. The attachment of the latter to the pterygoid bone is similar to the condition in T. tetradactyla (Fig. 11). Endo (1998) described a single mylohyoideus in Manis javanica (Sunda pangolin), but gave no details about the origin of the muscle's attachment to the skull. Previous description appeared to suggest the absence of a true intermandibularis anterior (sensu [START_REF] Diogo | From fish to modern humans -comparative anatomy, homologies and evolution of the head and neck musculature[END_REF] in pangolins. This is congruent with the presence of a fused symphysis.

However, further dissections are needed to verify the presence of this muscle. Edgeworth (1923) reported the early differentiation of the thyrohyoideus and the sternothyroideus from the rectus cervicis, describing the origin and insertions of these muscles, which are similar to those in anteaters. The author also described the presence of the larynx dilator cricoarytenoideus posterior ("crico-arytenoideus posticus"), the arytenoideus, and the thyroarytenoideus. As in anteaters, the thyroarytenoideus arises from the basal part of the thyroid cartilage and inserts on the arytenoid cartilage, and is divided in two parts that are designated as superior (thyroarytenoideus pars lateralis) and the smaller inferior (thyroarytenoideus pars medialis; Figs. 8 and 12). In Manis spp., the origin of the thyrohyoideus pars medialis is located on a median posterior process (Edgeworth, 1923), which is absent in the thyroid of anteaters. The arytenoideus lateralis is illustrated, as well as the cricothyroideus. Edgeworth (1923) did not report the division of the former in two parts, as is the case in anteaters. Both stylopharyngeus and the constrictores pharingis were also described, with no differences to report.

Despite several studies dedicated to the head musculature of pangolins (e.g., [START_REF] Macalister | Report on the anatomy of insectivorous Edentates[END_REF][START_REF] Windle | On the myology of the Edentata[END_REF]Edgeworth, 1923;[START_REF] Imai | The facial muscles of Manis pentadactyla Linne[END_REF]Endo et al., 1998), these articles present virtually no information concerning volume or mass ratios and references to the functional aspect are anecdotic.

The different nomenclatures used by each author and the different level of detail, associated with poor illustration, call for a unifying description of the musculature of pangolins. Future research on the pangolin head musculature would greatly contribute to assess the putative morphological convergence of their masticatory apparatus with that of anteaters. Key questions, like the existence of an intermandibularis anterior (sensu [START_REF] Diogo | From fish to modern humans -comparative anatomy, homologies and evolution of the head and neck musculature[END_REF], and the biomechanics of the pangolin masticatory apparatus would much benefit from a thorough review. In particular, the putative absence of an intermandibularis anterior in pangolins suggests a decreased degree of symphysial mobility when compared to anteaters. Furthermore, pangolins lack dorsal canaliculi, structures hypothesized to be associated to the coordination of the mediolateral rotation of the mandibles in anteaters (Ferreira-Cardoso et al., 2019). A quantitative assessment using modern techniques is key to associate these morphological traits to function.

Comparison with aardvark myology

The head muscles of the aardvark (Orycteropus afer), a myrmecophagous tubulidentate, ,have been the subject of several studies [START_REF] Humphry | On the myology of Orycteropus capensis and Phoca communis[END_REF][START_REF] Galton | XII. The myology of the upper and lower extremities of Orycteropus capensis[END_REF][START_REF] Windle | On the myology of the Edentata[END_REF][START_REF] Bender | Die Halsorgane von Orycteropus afer= capensis (Pallas) und Tamandua tetradactyla L. Denkschriften Der Medicinisch[END_REF][START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Although information on volume, mass, or rations is currently unavailable for head muscles, the masticatory, intermandibular, and hyoid musculature is relatively welldescribed and illustrated [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Similarly to other myrmecophagous species, the aardvark also possesses an elongated and specialized tongue (Goździewska-Harłajczuk, Klećkowska-Nawrot, & Barszcz, 2018), an elongated snout, and a regressed dentition lacking enamel. However, the aardvark presents a developed ascending ramus of the mandible, with prominent coronoid and condylar processes, and a broad masseteric fossa (e.g., [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF]Ferreira-Cardoso et al., 2019). The aardvark is also able to chew (Patterson, 1975).

The masseter of O. afer has been characterized as thin and flat [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF], but it is fan-like (vertical to longitudinal fibers) and presents a pars reflexa posterodorsally [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. In the absence of more details, it appears that the architecture of the masseter of O. afer is more complex than that of anteaters and pangolins. Unlike anteaters, O. afer presents a zygomaticomandibularis that inserts on the lateral surface of the mandible dorsally to the masseter. This muscle has vertically oriented fibers and originates along the jugal and the anterior part of the zygomatic process of the squamosal [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. It is probably not related to the masseter pars zygomatica of anteaters, as its insertion on the mandible is much more anteroventral and its origin further apart from the temporal fossa [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF]. The temporalis of O. afer also differs from that of anteaters as it extends dorsally and posteriorly into the cranial vault and covers both lateral and medial surfaces of the coronoid process, as well as its anterior and posterior margins [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF].

The pterygoideus complex in O. afer presents some differences when compared to that of anteaters [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Its pterygoideus medius presents three parts, while only two were identified in M. tridactyla and T. tetradactyla, and a single in C. didactylus. The pterygoideus externus is composed of a single part arising from the alisphenoid bone which makes it probably homologous to the pars inferior of the same muscle in anteaters (Fig. 5). As in pangolins, the aardvark presents a pterygotympanicus that originates on the ectotympanic and displays a tendinous connection to the tensor veli palatini, on the palate [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. The association of the pterygotympanicus with the tensor veli palatini suggests that both muscles might aid in the elevation of the soft palate by the levator veli palatini [START_REF] Auer | Equine surgery[END_REF][START_REF] Kishimoto | Three-dimensional imaging of palatal muscles in the human embryo and fetus: development of levator veli palatini and clinical importance of the lesser palatine nerve[END_REF]. T. tetradactyla and M. tridactyla lack both the pterygotympanicus and a separate tensor veli palatini. C. didactylus lacks the former, but presents a tensor veli palatine in close association with the posterior fibers of the pterygoideus medius on the palate.

O. afer presents a longitudinal "intermandibularis" that takes its origin on the hyoid and sends two tendons that insert anteriorly on the ventrolateral surface of the mandibles [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF]. [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF] suggested that this muscle might correspond to the mylohyoideus, but the attachment to the mandible and the longitudinal orientation resemble more those of a digastricus pars anterior [START_REF] Turnbull | Mammalian masticatory apparatus[END_REF]Gray, 1995). Inversely, both [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF] and [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF] suggested that the transversely oriented muscle attaching medially to the posterior half of the mandibles is a "digastricus anterior". This muscle presents a variable median raphe, such as the mylohyoideus musculature in anteaters and other mammals [START_REF] Edgeworth | On the development and hyoid of the mandibular and hyoid muscles of mammals[END_REF][START_REF] Saban | Musculature de la tête[END_REF][START_REF] Turnbull | Mammalian masticatory apparatus[END_REF], and it does not connect to the digastricus pars posterior [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Therefore, we propose that the "digastricus anterior" (sensu [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF][START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF] of the aardvark is a mylohyoideus pars anterior. We also propose that the "intermandibularis" of [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF] and [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF] is homologous to the geniohyoideus of anteaters, as both are longitudinally oriented, present an anterior bifurcation of the muscular fibers, and take their origin on the ceratohyal and basihyal. While we cannot confirm the correct identity of these muscles in O. afer, it is clear that, as in pangolins, both pars anterior and posterior of the digastricus are present. Both of these muscles are absent in anteaters.

Despite being elongated, the tongue of the aardvark does not attach to the sternum like in anteaters [START_REF] Windle | On the myology of the Edentata[END_REF][START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Both the genioglossus (which forms the base of the tongue)

and the hyoglossus attach to the hyoid system [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Additionally, a separated sternohyoideus is present in the aardvark [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. In anteaters, hyoglossus and sternohyoideus merge to form the extremely long sternoglossus [START_REF] Edgeworth | The cranial muscles of vertebrates[END_REF]Naples, 1999). The tongue musculature of the aardvark therefore presents a structure similar to other mammals, such as sloths or rats [START_REF] Greene | Anatomy of the rat[END_REF]Naples, 1986).

The hyoid-thyroid and thyroid-cricoid musculatures were described by [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. This author omitted any references to the ceratohyoideus, but this muscle was illustrated by [START_REF] Edgeworth | On the masticatory, intermandibular, and hyoid muscles of Orycteropus capensis[END_REF],

under the "branchio-hyoideus" designation. This muscle serves both as a stabilizer of the hyoid apparatus, as well as a probable depressor of the pharynx [START_REF] Reidenberg | Anatomy of the hyoid apparatus in Odontoceti (toothed whales): specializations of their skeleton and musculature compared with those of terrestrial mammals[END_REF]. Sonntag (1925) also described the crocothyroideus, although no reference was made to the subdivision of this muscle. Apart from the absence of the arytenoideus in O. afer, the description of the remaining muscles is similar to those found in anteaters. Further comparison, mainly regarding the shape and size of these muscles, is not possible with the details available from the literature.

The aardvark facial muscles are also different from anteaters, as suggested by [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF] and include a buccinatorius internus, which consists of a thin sheet in the aardvark. The aardvark presents a fleshy "levator nasi" that arises from the zygomatic process of the maxilla and extends to the anterior part of the snout, where it contributes with muscular fibers to the "levator labii superioris alaeque nasi" [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. The "levator nasi" appears to be homologous to the maxillolabialis of anteaters. In O.

afer, the maxillolabialis lacks long tendons anteriorly and assumes a dorsal position in the snout [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Whereas in anteaters we identified six separate muscles associated to the upper lip and buccal commissure, the single muscle "levator labii superioris alaeque nasi" appears to be responsible for elevating and retracting the snout. This muscle is also associated to the large sheet-like "levator nasolabialis" that arises from the frontal bone and inserts on the anterior tip of the snout and upper lip [START_REF] Sonntag | A monograph of Orycteropus afer. -I. Anatomy except the nervous system, skin, and skeleton[END_REF]. Again, this condition contrasts with the much smaller dilator nasi in anteaters (Fig. 6), both in size, origin, and length of muscular fibers.

Although myrmecophagous, the masticatory apparatus of aardvarks is functionally different from that of anteaters. The biomechanics of their masticatory apparatus has not yet been quantitatively assessed, but the muscular and bone anatomy already indicate that movements and forces involved will be highly divergent from those of anteaters. The large temporalis and masseter muscles, the presence of an ossified zygomatic arch, and the fused mandibular symphysis suggest significant functional differences. The presence of a vertically oriented zygomaticomandibularis also suggests a more important vertical component of force when compared to anteaters. The aardvark actively chews in order to eat cucumberlike plants from which they take their water (Patterson, 1975). The articular condyle is well dorsal to their tooth row, which typically allows for an increase in the momentum of force applied to food item [START_REF] Greaves | The mammalian jaw : a mechanical analysis[END_REF]. These are both functional and phylogenetic constraints that likely affect the tongue movement and speed of ant and termite intake.

Conclusion

Here we described and illustrated the masticatory apparatus, hyoid, thyroid, and sternum musculatures of the three genera of extant anteaters. While T. tetradactyla and M. tridactyla showed very similar morphologies, the masticatory apparatus of C. didactylus was shown to be more different than previously thought. However, we suggested that different morphologies, mainly those of the temporalis and masseter complexes, allow very similar functions. We further compared data from the literature and showed that the biomechanics of anteaters may well differ from that of pangolins, despite of the ecological convergence (McGhee, 2011). We also compared the head musculature of anteaters with that of the aardvark and show that they differ in some key aspects, mainly related to the tongue and masticatory musculature. Further studies will be needed to assess biomechanical differences, notably the magnitude of forces applied to the mediolateral rotation of the lower jaws (e.g., [START_REF] Oron | A cineradiographic and electromyographic study of mastication inTenrec ecaudatus[END_REF], and to characterize jaws movement in anteaters and pangolins.

Chapter 3: Morphological evolution, integration and modularity

3.1-Variation and covariation

Regardless of the process by which homoplasy is produced, evolutionary convergence is extremely common in nature. The reason why convergence is that ubiquitous is that life on Earth occupies just a small fraction of the theoretical morphospace [START_REF] Mcghee | Theoretical morphology: the concept and its applications[END_REF]. Shapes are limited by functional constraints, since mutations often produce life forms that are lethal. Additionally, morphology is limited by developmental constraints, which derives from the fact that organismal differentiation is conditioned to the original cell, the genetic coding, the interaction between cell tissues, and to all the geometric, physical, and chemical laws to which that mother cell is subjected to (McGhee, 2011). Constraints either prevent or shift the direction of evolutionary change, thus channeling evolution while restricting the evolvability of a biological system (Klingenberg, 2005). Evolvability is the degree to which an organism can respond to selection or evolve due to drift. The more evolvable a system, the more directions it can vary within the theoretical morphospace (Klingenberg, 2005). A constraint is considered to be "positive"

when evolvability is channeled (canalization; see below) towards specific directions in the morphospace, and "negative" when evolvability is reduced in every directions (Klingenberg, 2005). Additionally, constraints can be separated in absolute and relative constraints. The first are rare, if not inexistent, in nature, as they assume that all variation is contained in a subspace, with null variation along the remaining morphospace axes (Klingenberg, 2005). Relative constraints result in differential variation between axes of the morphospace, causing some axes to have a greater propensity to suffer selection or drift, therefore increasing the evolvability of certain traits to the detriment of others (Klingenberg, 2005).

Evolution is thus a result of a trade-off between natural selection, functional constraints, and the developmental processes. As previously referred, with his "loi de correlation des formes", Georges Cuvier proposed that each species was perfectly adapted to its environment and that its body parts were correlated, so that one could predict the shape of one part in the presence of another. The correlated evolution of morphological traits would be formalized by Olson and Miller (1958) as morphological integration.

However, as opposed to Cuvier's ideas, the correlation of morphological traits is not strictly due to adaptation to a functional optimum. Integration arises at both the intra-individual and the population levels (Cheverud, 1996). Intra-individual integration comprises both functional and developmental aspects, corresponding to the two sets of constraints that limit existing shape in the theoretical morphospace (McGhee, 2011). Mandibular occlusion is a typical example of a process originating functional integration, as it depends on a coordinated variation of size and shape between the upper and lower jaws.

Developmental integration occurs during the formation process of morphological structures. For instance, integration can be introduced due to high levels of growth hormone that promote structural growth (e.g., limb long bones) and thus increase covariation between associated morphological traits (Cheverud, 1996).

Integration occurring at the population level can be divided in genetic and evolutionary components (Cheverud, 1996). Logically, both intra-individual and population levels are inter-related. Genetic integration occurs when integrated sets of morphological traits are inherited. The morphological expression of genetic integration is developmental integration. Cheverud (1996) sets the difference between both types of integration arguing that developmental integration is related to the physiological effects of genes occurring in each individual, while genetic integration involves the transfer of integration from one generation to another within a population. Genetic integration can be exemplified by the inheritance of proportionally large hind-and forelimbs [START_REF] Leamy | Genetic and environmental correlations of morphometric traits in randombred house mice[END_REF]. Limb lengths covary due to genetic integration of two distinct developmental processes. Finally, evolutionary integration is a coordinated evolutionary trend of morphological elements, caused by both inherited integration and the effect of natural selection on a set of traits [START_REF] Felsenstein | Phylogenies and quantitative characters[END_REF].

If Cuvier described what can be called, in modern terms, functional integration, Étienne Geoffroy Saint-Hilaire and von Baer works orbit around the concept of developmental integration. If the first saw a common topology to all vertebrates, highlighting a common plan from which they derived to adapt to the most contrasting environments, the second observed structural differentiation and interaction, and somatic growth during ontogeny. However, none of them had the knowledge and tools to fully understand the implications of developmental integration and the full extent of its complexity. How important is the intrinsic tendency of biological systems to generate variation? If we consider the Bauplan or the 'archetype' of a given species as a cluster of individualized developmental processes, to which degree does it influence the evolution of its lineage?

Developmental constraints are the main factors introducing covariation between morphological traits (Hallgrímsson et al., 2009), and given that certain sets of conditions are more likely to evolve than others, strong correlation between traits might constitute an evolutionary constraint (Klingenberg, 2005).

As such, the levels to which integration occurs in organisms are inter-related and inter-dependent.

Nevertheless, developmental integration appears to have a predominant role in maintaining the unity of an organism. When looking at the skeleton, the topology and connectivity of elements are extremely similar in elephants and mice despite the obvious difference of functional constraints and selective pressures acting on animals with such different sizes and ecologies. Covariation of morphological traits arises from two different types of mechanisms (Klingenberg, 2005). The first type consists of direct interactions between developmental pathways (Fig. 5); a factor affects pathway "A", with a posterior interaction between pathways "A" and "B" causing trait covariation (Fig. 5). Variation by direct interaction can also be introduced when one factor affects one precursor pathway "Z" that posteriorly splits into pathways "C" and "D"; traits resulting from "C" and "D" covary due to a factor acting on "Z" (Fig. 5). The second interaction is designated parallel variation and occurs when variation is generated by the action of a factor over multiple pathways simultaneously (Fig. 5). This mechanism can be typically exemplified as a result of the action of environmental factors over a series of developmental processes (e.g., temperature differences; Klingenberg, 2005). In such cases, covariation between traits results from an external factor with no interaction between pathways. Both direct interaction and parallel variation can happen simultaneously, with covariation between traits being strengthened by both pathway interactions and the action of an external factor. Covariation of phenotypic traits arising due to interactions between several developmental pathways has an underlying genetic basis, as allelic differences are a source of variation in the genes associated to such pathways (Klingenberg, 2005). Briefly, allelic variation at a given locus results in pleiotropy. Pleiotropy can be separated into two categories that correspond to the two types of developmental interactions described above (Klingenberg, 2005). [START_REF] Hadorn | Zur Pleiotropie der Genwirkung[END_REF] defined "primary" pleiotropy as the direct consequence of the constitution of cells that form traits (shared upstream genetic variation), which corresponds to the parallel variation of developmental pathways. On the other hand, "secondary" pleiotropy results from the transmission of variation generated in one cell population to another (genetic variation transmitted downstream), which corresponds to the direct interaction between developmental pathways. The categorization of pleiotropy, signaling interaction, and its consequences to developmental covariation is a complex subject on which thorough reviews and discussions have been provided elsewhere [START_REF] Workman | Analysis of quantitative trait locus effects on the size and shape of mandibular molars in mice[END_REF][START_REF] Klingenberg | Integration, modules, and development: molecules to morphology to evolution[END_REF]Klingenberg, , 2005)). Here we aimed to give a simple description of pleiotropic effects as a source of covariation, and thus the bases of integration produced by developmental processes.

3.2-Modularity

Regardless of the type of integration concerned, its magnitude is not constant within an organism.

Groups of traits presenting strong and numerous interactions can be highly integrated internally (modules; Fig. 6). Each of these modules presents fewer and weaker interactions with other modules (Cheverud, 1996;Wagner, 1996). A phenotypic module can be defined as a unit with a strict functional role and strong pleiotropic effects of genetic variation [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]Wagner, 1996). Modularity can be considered either as an inherent property of organismal development, or as a byproduct of natural selection (Wagner, 1996).

From the first perspective Wagner (1996) sees modularity as a result of the living being as a selfmaintaining system (i.e., as a result of the chemistry that defines the structural organization of cells, tissues, organs, etc.). In this sense, modularity exists independently of function and could be compared as a modern concept for Saint-Hilaire's hypothesis of an intrinsic common organization to all beings. The second perspective on modularity is based on the formulation of morphological integration given by Olson andMiller (1951, 1958), which was then adopted and developed in several studies of modularity and integration (e.g., Cheverud, 1982;Goswami, 2006). It assumes that integration of functionally associated traits is selected, thus promoting modularity (Wagner, 1996). Modularity is conceptually hierarchical, with small and highly integrated modules being grouped in larger and less integrated ones (Klingenberg, 2005;Goswami, 2006). The mammalian skull is a classic example of modularity, with the skull being typically split between facial and neurocranial modules [START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF]. Within each module, the functional complexes (parcellation). If we take as an example, once again, the process of occlusion between the upper and lower jaws, we would expect to observe an increase in covariation between these two blocks of traits due to a selective pressure favoring pleiotropy among them (Klingenberg, 2005). By a process of parcellation, pleiotropy is maximized among the traits involved in mastication, and reduced among these and other traits with different functional demands. From here is derived the concept of genetic module, a group of loci strongly integrated due to pleiotropic effects, affecting the developmental pathways of morphological traits sharing the same function (functional modules; Wagner and Altenberg, 1996). Modularity can be represented by a "phenotype-genotype map", a direct correspondence between gene variation and differences in phenotype (Wagner and Altenberg, 1996).

From the previous two paragraphs, one can deduce that the concept of modularity is able to include both Cuvier's functionalism and Saint-Hilaire's "essential similarity" (Bauplan). Although not explicitly, the two anatomists focused on two different aspects of phenotype evolution, which are important to define at this point. The first one is variation, which was already used here, and consists of measurable differences among or between individuals of a sample (Wagner and Altenberg, 1996). The second one is "variability", which is the propensity of a phenotypic trait to vary, and correspond to a trait response to environmental and genetic factors (Wagner & Altenberg, 1996). Phenotypic variation can be simply quantified by a measure of dispersion (e.g., phenotypic variance), while the quantification of variability is less straightforward, requiring more complex designs (Wagner & Altenberg, 1996). Nevertheless, phenotypic variation can be used as a rough proxy for variability, since if variation of a module within an organism is high, then one can assume that the variability is high too. Similarly, if a given module presents a weak variation, one can suspect the existence of constraints on variability [START_REF] Alberch | Morphological Variation in the Neotropical Salamander Genus Bolitoglossa[END_REF]. Epistatic effects, the influence of one gene locus over the effects of other loci, control genetic variability and have an impact on the evolvability of phenotypic traits. [START_REF] Waddington | Canalization of development and the inheritance of acquired characters[END_REF] first introduced the concept of canalization. According to [START_REF] Waddington | Canalization of development and the inheritance of acquired characters[END_REF], canalization is the tendency of a developmental process to produce similar phenotypes independently of minor variations in environmental conditions.

Developmental processes are usually canalized in organisms subjected to natural selection. [START_REF] Waddington | Canalization of development and the inheritance of acquired characters[END_REF] used the genotype of Drosophila to demonstrate this, arguing that there is much less genetic variability in the wild type than in mutants. Canalization buffers the phenotype not only against environmental variations, but also allelic variation [START_REF] Waddington | Canalization of development and the inheritance of acquired characters[END_REF]. A strong stimulus (e.g., environmental; mutation) might cause this buffering mechanism to fail (de-canalization) and thus may allow for cryptic genetic variation to be expressed in the phenotype [START_REF] Dworkin | Canalization, cryptic variation, and developmental buffering: a critical examination and analytical perspective[END_REF]. The phenomenon of canalization can be defined and quantified on the basis of the phenotypic variance observed between two populations exposed to two distinct environments [START_REF] Dworkin | Canalization, cryptic variation, and developmental buffering: a critical examination and analytical perspective[END_REF]Fig. 8-2). The "canalized" population presents a non-significantly different variance around a mean measure (e.g., least-square means) between two environmental conditions, while the "de-canalized" population shows an increase in variance as a result of cryptic genetic variation released for selection [START_REF] Dworkin | Canalization, cryptic variation, and developmental buffering: a critical examination and analytical perspective[END_REF]. Hallgrímsson et al. (2009) used the scaled variances of eigenvalues to show that inbred mutant populations of mice showed not only a shift in means, but also an increased phenotypic variation when compared to the wild types of several species of muroid rodents (Jamniczky & Hallgrímsson, 2009). This is an empirical example of decanalization due to a stimulus in developmental processes (i.e., induced mutations). Hallgrímsson et al. (2009) also showed that overall integration tended to increase in mutant populations, when compared to the wild types. Such discoveries show the complexity of the processes producing covariation, while highlighting that natural selection and canalization processes synergistically play a role in the integration of biological structures.

In addition to the increase of integration, Hallgrimsson et al. ( 2009) also showed that changes in variation among mutant lineages are not evenly distributed across all traits (Fig. 8d in Hallgrímsson et al., 2009). External stimuli affect some morphological modules, while having little or no effect in the remaining traits. This supports the previously presented consideration that modules allow for the evolution of complex phenotypes. Organisms are modular, showing discrete parts evolving differently while maintaining a common evolutionary trajectory that enables to preserve a common functionality. [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF] arguably proposed that modularity is the most important facilitator of evolution. The author considers that this evolutionary relevance arises from three different processes occurring within a module: dissociation, duplication and divergence, and co-option [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. Dissociation can be temporal, spatial, or could occur in the interaction between modules. Temporal dissociation, or heterochrony, occurs when the relative timing of developmental processes changes during evolution. Spatial dissociations (heterotypy) refer to shifts in spatial relationships like changes of the cell type in which a gene is expressed, the production of repeated structures, or the modification of relative proportions of structures [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. Finally, dissociation of developmental modules occurs when related processes can occur independently. For instance, the development of the lens in amphibian eye can still occur if the retina is removed [START_REF] Jacobson | Inductive processes in embryonic development[END_REF]. This means that the two structures became two separate developmental modules. Another example can be found in gene duplication, in which function-changing mutations may occur in the copied gene. If these mutations are not deleterious, then natural selection starts to act on the divergent trait condition, possibly creating a new functional module (through integration, parcellation, or both). For example, the bone morphogenetic proteins (BMP), responsible for bone growth, constitute a family of related proteins that have been experimentally shown to have distinct expression sites [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. In the first place duplication might have occurred, with each protein evolving distinct functions and thus originating a modular pattern. The third category of processes contributing for modular evolution is co-option. This consists of the adaptation of a structure to a different functional role than that ancestrally observed (exaptation following [START_REF] Gould | Exaptation -a aissing term in the science of form[END_REF]. The Paleozoic radiation of jawed vertebrates (Gnathostomata) resulted from an evolutionary advantage that is an illustrative example of a combination of spatial dissociation, duplication and divergence, and co-option [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. The lower jaw evolved from the most anterior of the seriously homologous gill arches, which was co-opted to grasp prey. A new function acted upon by a different selection pressure resulted in the evolution of an extremely specialized and ultimately diversified structure, without lethally disrupting the gill arches modules. If on one side spatial dissociation, duplication, and co-option promote evolvability of complex organisms, they are also the reason why modules are repeated and conserved within and across taxa, or across different hierarchical levels of organismal organization (e.g., molecular, cellular, tissue-level; [START_REF] Brandon | Evolutionary modules: conceptual analyses and empirical hypotheses[END_REF]. The development of completely unrelated new modules is theoretically rare, if not impossible, as the basic units of organismal construction are common across the Metazoa ("standard parts"; [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF][START_REF] Winther | Evolutionary developmental biology meets levels of selection: modular integration or competition[END_REF]. Modules are formed from the clustering of standard parts, with the highest levels being ubiquitous across tetrapods, vertebrates, or even the entire biological spectrum (Riedl, 1978). All in all, morphological innovation by the generation of a "new module" tends to occur by the differentiation of repeated elements [START_REF] Simon | The Architecture of Complexity[END_REF][START_REF] Akam | Homeotic genes and the control of segment diversity[END_REF][START_REF] Muller | Novelty in evolution: restructuring the concept[END_REF].

It becomes clear that modularity is an evolved property of biological organisms (Wagner & Altenberg, 1996). Consequently, modules can be seen as main drivers of organismal evolution, or evolutionary units. In sum, modules allow for the differential evolution of complex organisms as their semi-independence grants more degrees of liberty to certain developmental processes that become free from the constraints of a fully integrated structure (Riedl, 1978). If the coordinated variation of discrete parts of an organism in different directions of the morphospace appears to boost organismal evolvability, to what extend does that covariation limit or facilitate the evolvability within a module? The role of integration as either a constraint or a facilitator of evolution has been discussed in several works (Goswami & Polly, 2010;Parr et al., 2016;Felice & Goswami, 2018;Felice et al., 2019). [START_REF] Martin | The Evolutionary Value of Recombination Is Constrained by Genome Modularity[END_REF] used the DNA of a plant virus (Maize streak virus) to show that genes with highly complex interactions (highly integrated networks) are less likely to maintain their function posterior to horizontal transfer. As a result, the contribution of gene recombination to evolvability is inversely proportional to integration of interaction networks. This supports the hypothesis that considers integration as an evolutionary constraint within a module. However, other studies found some evidence that integration may increase the evolutionary rate of a module. Goswami and Polly (2010) used a measure of morphological disparity to show that, in the skull of carnivores and primates, highly integrated modules tend to present lower disparity values, which was interpreted as a constraint to modular evolvability. However, they also showed that some highly integrated modules present high disparity, supporting the facilitation hypothesis. Parr et al. (2016) equally found evidence for the validity of both hypotheses within a sample. Goswami and Polly (2010) showed that integration and disparity are often simply uncorrelated.

3.3-The skull of placental mammals

In the previous section, I introduced the study of modularity of the placental skull. As in all vertebrates, the skull of placental mammals is a complex structure both developmentally and phylogenetically [START_REF] Klaauw | Size and position of the functional components of the skull. A contribution to the knowledge of the architecture of the skull, based on data in the literature[END_REF]Cheverud, 1982a;[START_REF] Gans | Stages in the origin of vertebrates: analysis by means of scenarios[END_REF][START_REF] Hanken | Evolution and development of the vertebrate skull: the role of pattern formation[END_REF]. The skull can be generally divided into three parts: neurocranium; viscerocranium; dermatocranium [START_REF] Hanken | Evolution and development of the vertebrate skull: the role of pattern formation[END_REF].

The neurocranium develops as a cartilage at the base of the brain and surrounds the sensory organs (inner ear, eye, olfactory organ; [START_REF] Friede | Normal development and growth of the Human neurocranium and cranial Base[END_REF][START_REF] Hanken | Evolution and development of the vertebrate skull: the role of pattern formation[END_REF][START_REF] Jin | Development and Growth of the Normal Cranial Vault : An Embryologic Review[END_REF]. This cartilage is replaced by the skull in later stages. Ventral do the neurocranium, the walls of the primitive pharynx give origin to the cartilaginous (later ossified) viscerocranium or branchial arches, from which structures like the mandible, the middle ear ossicles, and the hyoid apparatus derived during the evolution of tetrapods [START_REF] Hanken | Evolution and development of the vertebrate skull: the role of pattern formation[END_REF][START_REF] Donoghue | Early evolution of vertebrate skeletal tissues and cellular interactions, and the canalization of skeletal development[END_REF]. This part of the skull normally counts seven arches in total [START_REF] Beer | The development of the vertebrate skull[END_REF]. Lastly, the dermatocranium consists of ossified plates that protect the brain dorsally and laterally and also includes mineralized tissues (e.g., dentine, enamel; [START_REF] Schilling | Development, growth, and evolution : implications for the study of the hominid skeleton[END_REF].

The dermatocranium and viscerocranium differentiate from neural crest-derived mesenchyme, with cells from the dermatocranium migrating anteriorly to form the face [START_REF] Noden | The role of the neural crest in patterning of avian cranial skeletal, connective, and muscle tissues[END_REF][START_REF] Osumi-Yamashita | Mammalian Cranial Neural Crest Cells and Facial Development. (cranial neural crest cells/facial development/mammal/retinoic acid receptor/gene expression)[END_REF][START_REF] Osumi-Yamashita | The contribution of both forebrain and midbrain crest cells to the mesenchyme in the frontonasal mass of mouse embryos[END_REF]. On the other hand, the neurocranium, as the axial appendicular skeleton, is mostly derived from paraxial-mesoderm [START_REF] Wilkinson | Expression pattern of the mouse T gene and its role in mesoderm formation[END_REF][START_REF] Couly | The triple origin of skull in higher vertebrates: a study in quail-chick chimeras[END_REF]. The three parts of the cranium can also be grouped according to their ossification type [START_REF] Schilling | Development, growth, and evolution : implications for the study of the hominid skeleton[END_REF]. The dermatocranium is a membrane bone, ossifying within the dermis, while the viscerocranium and neurocranium form as a cartilage which is secondarily ossified (e.g., [START_REF] Jollie | The head skeleton of a new-born Manis javanica with comments on the ontogeny and phylogeny of the mammal head skeleton[END_REF]). The embryonic origin of the skull is relatively conserved across vertebrates (Fig. 7; Piekarski et al., 2014). In the mouse, neural crest-derived bones include the nasals, premaxillae, vomers, septomaxillae, maxillae, lacrimals, frontals, jugals, sphenoid complex, palatines, pterygoids, squamosals, and medial elements of the interparietals [START_REF] Chai | Fate of the mammalian cranial neural crest during tooth and mandibular morphogenesis[END_REF][START_REF] Jiang | Tissue Origins and Interactions in the Mammalian Skull Vault[END_REF][START_REF] Koyabu | Paleontological and developmental evidence resolve the homology and dual embryonic origin of a mammalian skull bone, the interparietal[END_REF]. Dentaries and teeth are also derived from the neural crest. Mesoderm-derived ossifications includes parietals, lateral elements of the interparietals (tabulars; [START_REF] Koyabu | Paleontological and developmental evidence resolve the homology and dual embryonic origin of a mammalian skull bone, the interparietal[END_REF], supraoccipitals, exoccipitals, and basioccipital. In mammals, the skull has been traditionally divided into two developmentally separated parts (or modules) roughly based on their embryonic tissue origin: the face and the "neurocranium" [START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF]. The face consists of all neural crest-derived bones, with the exception of the squamosal, the alisphenoid, and the medial parts of the interparietal (postparietals; [START_REF] Koyabu | Paleontological and developmental evidence resolve the homology and dual embryonic origin of a mammalian skull bone, the interparietal[END_REF]. The former two were integrated into the neurocranium, becoming an integral part of the lateral wall of the braincase to accommodate the growth of the cerebral hemispheres during the evolution of mammals [START_REF] Goodrich | Studies of the structure and development of vertebrates[END_REF][START_REF] Morriss-Kay | Derivation of the mammalian skull vault[END_REF]. The interparietal is included in the cranial vault, surrounded by mesoderm-derived elements. The tissue origin, type of ossification, unit topology have been used as the basis for studies of modularity and development in mammalian skull (Hallgrímsson et al., 2004;Goswami, 2006;Porto et al., 2009;[START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF][START_REF] Evin | A test for paedomorphism in domestic pig cranial morphology[END_REF].

This brief introduction to the developmental origins of the mammalian skull is intended to present the complex character of this structure, but also its evolutionary conservatism across clades. In 1951, Everett Olson and Robert Miller introduced the principle of intercorrelation between linear measurements of the skull, which they would later call morphological integration [START_REF] Olson | A mathematical model applied to a study of the evolution of species[END_REF]. They hypothesized that the biological meaning of correlations between cranial distances could be related to either function (e.g., mastication), or development [START_REF] Olson | A mathematical model applied to a study of the evolution of species[END_REF]. Cheverud (1982) showed that the face of the rhesus macaque could be split in functional parts related to vision (orbital), olfaction (nasal), food taking/biting/sensing (oral), and food grinding (masticatory). The oral and masticatory functional components of the skull integrate the feeding apparatus, a part of the skull linked to food resources exploitation and intimately connected to radiations occurring during mammalian evolution (Schwenk, 2000). These radiations were possible due to the plasticity of the feeding apparatus (bone and interacting muscle tissue) despite a common Bauplan. Such adaptability has been evidenced from the intra-individual to the evolutionary level. The simple diet hardness reduction has been shown to decrease bone volume in rats [START_REF] Moore | Masticatory function and skull growth[END_REF]. This hypothetically resulted from the reduction of the contraction force applied by the masticatory muscles.

The feeding apparatus holds a significant number of adaptive traits, which makes it particularly susceptible to produce homoplasy in a comparative phylogenetic context. Many examples have been reported, whether we consider tooth shape [START_REF] Lazzari | Mosaic Convergence of Rodent Dentitions (JE Stajich[END_REF], jaw shape [START_REF] Mccurry | The remarkable convergence of skull shape in crocodilians and toothed whales[END_REF][START_REF] Page | Morphological convergence in 'river dolphin' skulls[END_REF], or tooth loss [START_REF] Charles | Under pressure? dental adaptations to termitophagy and vermivory among mammals[END_REF]. The morphological expression of genetic, developmental, and functional modules has been shown in a wide range of taxa and morphological structures (Cheverud, 1982a;Klingenberg et al., 2001;Goswami, Weisbecker, & Sánchez-Villagra, 2009;Suzuki, 2013;Parr et al., 2016;Goswami & Finarelli, 2016;Randau & Goswami, 2017;Felice & Goswami, 2018;Heck et al., 2018;Churchill et al., 2019;Randau, Sanfelice, & Goswami, 2019;Bardua et al., 2019). However, the vertebrate skull has been the focus of most researches on morphological modularity, mostly due to the highly diversified shapes that resulted from the radiation of Gnathostomes in the Paleozoic [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. Cheverud (1982[START_REF] Cheverud | Morphological integration in the saddle-back tamarin (Saguinus fuscicollis) cranium[END_REF] produced the first studies that aimed at measuring the correlation between functional, genetic, and phenotypic modules in the mammalian skull. The functional multiplicity of the skull offers the possibility to test hypotheses of modularity within a wellknown genetic and developmental framework (Cheverud, 1982a). Using inter-landmark distances and hierarchical clustering analyses, Cheverud (1982) found that the skull of the rhesus macaque was divided in eight phenotypic clusters, consisting of seven modules: frontal, parietal, occipital, orbital, small nasal, interactions (integration;Hallgrimsson et al., 2007). Hallgrimsson et al. (2009) used geometric morphometric methods to test five hypothesis of modularity based on developmental processes such as the two-module tissue origin hypothesis or a three-module muscle-bone interaction hypothesis. While not finding support for any of the hypothesis tested, Hallgrimsson et al. (2009) proposes that the developmental processes involved in the skull development are too complex to be represented by morphological covariation patterns. In sum, the skull covariation patterns should be considered as a mosaic of variation-generating processes whose imprints overlap in space (sometimes in time) and whose resulting structure is not easily predictable.

In the following article, I explore the patterns of intraspecific and interspecific modularity and integration of the skull of myrmecophagous placentals. I show that the modular architecture in these species is similar to that of other placental mammals, despite the some extreme cases of tooth loss and rostrum elongation. We discuss the implications of our results on the convergent evolution the myrmecophagous cranial phenotype.

Introduction

Modularity is probably the most ubiquitous characteristic of biological systems (Winther, 2001;Klingenberg, 2005). Developmental modules are organizational units of traits with underlying high density of pleiotropic interactions (Wagner, 1996;Klingenberg, 2005). Phenotypic modules are sets of traits that share putative functional roles and common developmental processes (Olson & Miller, 1958;Cheverud, 1982). Such constraints limit the axes along which the phenotype can vary within each module, and are potential generators of coordinated phenotypic variation (Hallgrímsson et al., 2007(Hallgrímsson et al., , 2009)).

Therefore, traits tend to be integrated within each module, varying semi-independently in relation to the whole system. Trait integration and modular organismal parcellation (the process of division in modules)

are suggested to play a crucial role in the evolution of complex structures by reducing adaptive redundancy [START_REF] Riedl | A systems-analytical approach to macro-evolutionary phenomena[END_REF](Riedl, , 1978;;Wagner & Laubichler, 2004). In other words, modularity allows functionally integrated traits to covary within a module, while limiting the effects of mutations or the action of directional selection on uncorrelated characters occurring in other modules. This trade-off between intrinsic organismal variation properties and specific adaptive landscapes might promote the evolvability of certain functional units (Riedl, 1978;Wagner, 1996;Wagner & Laubichler, 2004;[START_REF] Wagner | The road to modularity[END_REF]. As a result, testing of the modularity hypothesis and defining modular organisation has been the target of several studies in a wide range of organisms and body parts such as insect wings (Klingenberg et al., 2001;Klingenberg, 2009b;Suzuki, 2013), mammalian mandibles [START_REF] Klingenberg | Integration and modularity of quantitative trait locus effects on geometric shape in the mouse mandible[END_REF]Zelditch et al., 2008), limbs (Goswami, Weisbecker, & Sánchez-Villagra, 2009), and vertebrae (Randau & Goswami, 2017).

The correlations among traits of the cranium have been intensively studied in the vertebrate skull and explained in terms of functional and ontogenetic constraints. Investigations on the skull modularity and integration patterns have been conducted in birds [START_REF] Klingenberg | Evolutionary Covariation in Geometric Morphometric Data: Analyzing Integration, Modularity, and Allometry in a Phylogenetic Context[END_REF]Felice & Goswami, 2018), amphibians (Simon & Marroig, 2017;Bardua et al., 2019), reptiles [START_REF] Piras | Morphological 199 integration and functional modularity in the crocodilian skull[END_REF] and mammals (Hallgrímsson et al., 2004;Porto et al., 2009). The mammalian skull presents a modular pattern with a major separation between the face and neurocranium [START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF], as well as between the rostrum, vault, and basicranium [START_REF] Del Castillo | Skull ontogeny and modularity in two species of Lagenorhynchus : Morphological and ecological implications[END_REF]. Further regionalization of its modular architectures has been proposed (Cheverud, 1982;Marroig & Cheverud, 2001;Goswami, 2006) with the recognition of six modules corresponding to the oro-nasal, molar-palate, orbit, zygomatic archpterygoid, vault, and basicranium regions. These phenotypic modules have been suggested to correspond to both developmental and functional constraints, some specifically related to food detection and capture (oro-nasal), food processing (molar-palate), and origin for adductor muscles (zygomatic-pterygoid).

Shifts in diet are known to influence skull shape and produce distinct phenotypes across a wide range of vertebrates such as turtles [START_REF] Claude | Ecological correlates and evolutionary divergence in the skull of turtles: a geometric morphometric assessment (J Kim[END_REF], frogs [START_REF] Emerson | Skull shape in frogs: correlations with diet[END_REF], bats (Nogueira, Peracchi, & Monteiro, 2009), and carnivorous placentals and marsupials (Wroe & Milne, 2007). The morphological diversification of the feeding apparatus has played a major role in tetrapod radiations, varying from strong jaws with bone-crushing teeth to the edentulous and elongated jaws of ant-and termite-eating (i.e. myrmecophagous) mammals (Schwenk, 2000). The loss or reduction of teeth has occurred in all major mammalian clades (Meredith et al., 2009;Ferreira-Cardoso, Delsuc, & Hautier, 2019b) and is often associated to a specialized myrmecophagous diet (Davit-Béal, Tucker, & Sire, 2009;Meredith, Gatesy, & Springer, 2013). Myrmecophagy evolved independently in divergent placental lineages such as anteaters, giant armadillos, pangolins, aardwolves, and aardvarks. The evolution of these taxa towards this specialized diet led to an extensive rearrangement of the skull morphology (Patterson, 1975;[START_REF]Dietary specialization and variation in two mammalian myrmecophages (variation in mammalian myrmecophagy)[END_REF][START_REF] Rose | [END_REF][START_REF] Vizcaino | Mecanica masticatoria de Stegotherium tessellatum Ameghino (Mammalia, Xenarthra) del Mioceno de Santa Cruz (Argentina)[END_REF]Vizcaíno et al., 2009). These morphological changes occurred in the context of developmental conservatism of the mammalian skull.

Compared to toothed placentals, we predict that myrmecophagous mammals might present three main differences in covariance-generating processes. First, tooth reduction or absence should decrease variance generated by tooth development and eruption (e.g., Cheverud, 1996;Zelditch et al., 2008).

Second, the loss of masticatory function, mastication associated structures (e.g., zygomatic arch), and reduction of mastication muscles volume (Edgeworth, 1923;Yeh, 1984;Naples, 1999) should alter the covariance patterns at their origin in the skull. In chicken and mice, bone formation appears to be dependent on functional muscles that perform embryonic muscle contraction (Hall & Herring, 1990;Rot-Nikcevic et al., 2006). Third, the extreme snout elongation of myrmecophagous placentals, particularly anteaters, should add increasing amounts of variance in this part of the skull (Olson & Miller, 1958;[START_REF] Cardini | Larger mammals have longer faces because of size-related constraints on skull form[END_REF]Cardini, 2019a), somatic growth of bone tissues being one of the main processes contributing to structural covariation on the mammalian skull (Hallgrímsson et al., 2007(Hallgrímsson et al., , 2009[START_REF] Hallgrímsson | Integration and the developmental genetics of allometry[END_REF][START_REF] Gonzalez | Effects of growth hormone on the ontogenetic allometry of craniofacial bones[END_REF].

Here, we used exploratory and confirmatory methods to describe the previously unexplored modular architecture of 15 myrmecophagous placentals. We compared modularity and integration patterns between species in order to understand if the evolution towards myrmecophagy is reflected in a convergent change in cranial covariation/correlation patterns. We additionally performed a comparative analysis by adding 21 non-myrmecophagous sister taxa to compare cranial morphologies and to test if morphological adaptation towards myrmecophagy translated into similar rates of evolution among ant-and termite-eating placentals.

Materials and methods

Biological sampling

Skull We placed 54 three-dimensional landmarks on skulls using a Revware MicroScribe M 3D digitizer (Fig. 1; Table S1). We selected homologous anatomical landmarks for our morphologically diversified sample based on previous works (Goswami, 2006;Hautier et al., 2014Hautier et al., , 2017;;Ferreira-Cardoso et al., 2019a). Given that modularity analyses are based on the covariation/correlation structure of the data, we opted out the placement of semilandmarks to avoid autocorrelation issues (Cardini, 2019b). In a significant number of pangolin and anteater specimens (82% of our myrmecophagous sample) premaxillae were either absent, loosely attached, or broken, and were therefore not landmarked. Missing landmarks were estimated via thin plate spline interpolations (Claude, 2008), for each species, using the 'estimate.missing' function in geomorph v. 3.5.0 (Adams et al., 2017) in R (Team, 2013). Landmark sets were symmetrized (left side) and then subjected to species-specific Generalized Procrustes Analysis (GPA; [START_REF] Gower | Generalized procrustes analysis[END_REF]Rohlf & Slice, 1999) prior to modularity analyses. A single GPA was performed on the dataset for interspecific comparisons. The GPA scales to centroid size, optimally translates and rotates the specimens using least-squares criterion.

(2) extraction of a covariance matrix based on all configurations;

(3) extraction of the eigenvectors with corresponding positive eigenvalues resulting from the covariance matrix; (4) scaling the eigenvectors by using the eigenvalues; ( 5) calculation of the inter-trait Euclidean distances matrix from the scaled eigenvectors; ( 6) identification of trait clusters using Ward's clustering method. For the last step, we used the Gap statistic [START_REF] Tibshirani | Estimating the number of clusters in a data set via the gap statistic[END_REF] as implemented in the function 'clusGap' of cluster v.2.0.8 R package. For each species, we tested the splitting of the tree in 2 to 10 clusters. The preferred number of clusters was selected and, we then determined cluster composition with bootstrap resampling using the 'clusterboot' function in fpc R package [START_REF] Hennig | Cluster-wise assessment of cluster stability[END_REF][START_REF] Hennig | Dissolution point and isolation robustness: Robustness criteria for general cluster analysis methods[END_REF]. Whenever clusters were biologically meaningless (e.g., formed by two bilaterally symmetric landmarks) their number was reduced until they became integrated in larger ones, in order to avoid overfitting the data.

The second exploratory analysis performed (MCN) consisted of the association of three methods:

the RV coefficient [START_REF] Escoufier | Le traitement des variables vectorielles[END_REF]; the Reichardt and Bornholdt community detection method based on the spin-glass model [START_REF] Reichardt | Statistical mechanics of community detection[END_REF]; the consensus clustering in complex networks [START_REF] Lancichinetti | Consensus clustering in complex networks[END_REF]. Landmark configurations were subjected to a Generalized Procrustes Analysis [START_REF] Gower | Generalized procrustes analysis[END_REF]Rohlf & Slice, 1999) implemented in geomorph R package v.3.0.7 (Adams et al., 2017). All specimens were scaled to centroid size, optimally translated and rotated using least-squares criterion. We then used a similar approach to the one proposed by Suzuki (2013), in which a pairwise RV coefficient matrix (RVij Procrustes aligned coordinates) is converted into a weighted adjacency matrix, for each studied species. The Reichardt and Bornholdt community detection method was then used to recover a modular architecture corresponding the minimum energy state (Suzuki, 2013). Because the spin glass model includes several energy states near the minimum level, a total of 300 trials were run to find the modular architecture of each network. Increasing the number of trials did not improve the results and made the analyses extremely long. Given the multitude of slightly different solutions (module number and module composition), a consensus matrix Cij was built, with each case containing the probability of i and j to be clustered in the same module [START_REF] Lancichinetti | Consensus clustering in complex networks[END_REF]. The consensus matrix was then used to generate a new weighted adjacency matrix that was submitted to another set of 300 trials to recover modular architectures. In total, the spin glass -consensus matrix sequence was repeated three times for each species. The MCN was implemented with a custom code integrating the 'cluster_spinglass' function from the igraph v1.2.2 package [START_REF] Csardi | The igraph software package for complex network research[END_REF] in R (Team, 2013).

In order to test a priori hypotheses of modular partitioning of the skull, a matrix of trait correlations (congruent coefficient) was constructed for each species using the 'doctorr' function of the paleomorph v0.1.4 R package [START_REF] Lucas | paleomorph: Geometric Morphometric Tools for Paleobiology[END_REF]. Multiple modular architectures were tested using the 'EMMLi' function in the EMMLi v0.0.3 R package (Goswami & Finarelli, 2016). This approach selects the best model based on maximum likelihood, comparing models with different number of modules with different variations within the same model related to inter-and intra-modular correlation pattern heterogeneity (Goswami & Finarelli, 2016). EMMLi was performed twice for each species, with option abs set to FALSE in the second analysis in order to allow negative inter-modular correlations to be retrieved (Simon & Marroig, 2017). We tested 10 different modular architectures varying from a fully integrated skull (one single module) to the therian mammal six-module architecture (Goswami, 2006).

Our a priori architectures additionally included a variant of Goswami ( 2006)'s therian six-module architecture with the zygomatic process landmarks added to the zygomatic-pterygoid module, analogues of those previously tested by Hallgrímsson et al. (2004; three and six modules), and a variant of the therian six-module architecture with the oro-nasal module coded as unintegrated (Churchill et al., 2019). To this set of hypotheses, we added a classical division of the skull in two modules (face-neurocranium), as well as two architectures derived from the network analysis with the P. tricuspis and T. tetradactyla datasets, and two seven-module architectures [START_REF] Hallgrímsson | [END_REF]Goswami, 2006) modified according to EDMA.

The models tested are hereafter referred to in roman numerals (Models I-X) as presented in Table 1.

In addition to the correlation matrices calculated from the Procrustes aligned coordinates, modular architecture was tested on static allometry-corrected residuals extracted from a Procrustes ANOVA (shape ~ logarithm transformed centroid size) performed with the 'procD.lm' function in geomorph R package.

Modularity was not tested in species with non-significant allometric effect.

We additionally used the covariance ratio (CR; Adams, 2016) to test for a priori hypotheses of modular architecture using the 'modularity.test' function in geomorph R package. For each species, we submitted the most likely modular architecture to the CR test.

In order to remove correlation among modules that would result from pure architectural constraints and from the Procrustes analysis considering the skull as a whole, between-and within-modules correlations were tested using the MCN-derived architectures to divide the skull in individually Procrustes aligned modules. Pairwise partial least-squares analyses (PLS) were performed between all separatelyaligned modules, to assess the significance and degree of covariation of the two blocks. PLS were performed with the 'pls2B' function of the Morpho v2.6 R package [START_REF] Schlager | Morpho and Rvcg -Shape Analysis in R: R-Packages for Geometric Morphometrics, Shape Analysis and Surface Manipulations[END_REF]. This procedure was not repeated for the allometry-corrected shapes. Additionally, we used correlation matrices in order to calculate the average correlation within modules in order to compare the magnitude of integration between datasets with common and separated Procrustes superimpositions. Given that these tests aimed at providing an empirical example of the covariation introduced by Procrustes superimposition, they were performed for the two best sampled species only (P. tricuspis and T. tetradactyla).

Evolutionary modularity

In order to understand the interaction between snout elongation and modularity, we calculated mean shapes for each of our focal species and built a dataset (n = 36) integrating non-myrmecophagous sister taxa. Firstly, we visualized the skull shape variation on a principal component analysis [START_REF] Dryden | Multivariate shape analysis[END_REF]. We then performed a Procrustes ANOVA with the 'procD.lm' function in geomorph to assess the effect of log-transformed centroid size on shape, and extracted the residuals from this analysis (allometry-corrected shapes). We visualized the allometry-corrected data on a principal component space in order to describe changes associated to the first two principal components (PCs) explaining most variance. Secondly, we divided the skull shapes in rostrum and neurocranium (Model I) and used the 'compare.evol.rates' function in geomorph to obtain species evolutionary rates for the two modules (Drake & Klingenberg, 2010), using 10.000 iterations. We divided the skull in these two modules in order to understand if myrmecophagous species presented a higher evolutionary rate associated to changes in the rostrum. The phylogeny was generated from timetree.org (Kumar et al., 2017) and imported into Mesquite v. 3.6 (Maddison & Maddison, 2018) to add additional species and adjust node ages based on molecular phylogenies from Gibb et al. (2016) and [START_REF] Gaudin | Appendix 6 Extended abstract in French[END_REF]. We then applied the maximum-likelihood modular architecture selection described in the previous section on the interspecific dataset. We used the most likely architecture and calculated species evolutionary rates for each module. The evolutionary rates were plotted on a phylogeny using the 'plotBranchbyTrait' function of the phytools R package (Revell, 2012). Finally, we divided the dataset using dietary (myrmecophagous vs non-myrmecophagous) and taxonomic (myrmecophagous vs non-myrmecophagous within Atlantogenata and Laurasiatheria), in order to assess differences in evolutionary rates. We also compared these rates with a Marsupial outgroup and a Primate (outgroup to pangolins+carnivores). Significance levels were assessed via permutation tests [START_REF] Adams | Multivariate Phylogenetic Comparative Methods: Evaluations, Comparisons, and Recommendations[END_REF].

Comparison of covariance matrices

In addition to the modularity analyses, we used principal coordinate analysis (PCoA) in order to compare the covariance matrices of each species in the morphospace. First, we performed a common Procrustes superimposition of the entire dataset (n = 480). We performed a PCA on the aligned coordinates and extracted the first seven axes explaining 90% of the variance. We then computed 15 species-specific covariance matrices based on those seven principal components. Euclidean distances were calculated for all pairs of covariance matrices and compiled on a distance matrix. Finally, we performed a PCoA of the distance matrix.

We conducted a second set of analyses to assess the change in skull covariance patterns during ontogeny. We selected the two best-sampled species (T. tetradactyla and P. tricuspis), for which we had a wide range of sizes. In these two species, the absence of teeth hinders age determination based on tooth eruption. We thus used size as a proxy for age (Ferreira-Cardoso et al., 2019a). For each species, four categories were created corresponding to the first to fourth quantiles of the centroid size (stages 1-4).

Specimens in stage 1 presented skull traits associated to juveniles, such as unfused or loose basicranial and occipital sutures, or the presence of spongious bones. The remaining stages presented mainly differences in size and shape. We considered stage 1 as juveniles, stage 4 as mature adults, while stages 2 and 3 represent intermediate ages. For each species, we computed covariance matrices for each stage and then followed a similar procedure to the one described in the previous paragraph. The final PCoAs can be considered as an approximation of correspond to species ontogenetic trajectories of covariance (Mitteroecker & Bookstein, 2009).

Computation of covariance and squared distance matrices were respectively performed with the 'cov.group' and 'mat.sq.dist' functions of the vcvComp v1.0.1 R package (Le [START_REF] Maitre | Multivariate comparison of variance in R[END_REF].

Results

Exploratory analyses of modularity -MCN

The network analysis (MCN) retrieved a modular organization of the skull that varied between three to ten modules (Table S2). The most frequent architectures for each species varied from three to six modules, with a three-module architectures being the most frequent in five species, four modules in three species, five modules in two species, and a six-module architecture in four species (Table S2). When the number of modules was the same, they varied in composition between species. However, in most cases, the resulting modules either grouped functionally unrelated landmarks or showed gross modular partition (e.g., see Fig. S1). We frequently found clusters of landmarks belonging to the basicranium (e.g., landmarks from the foramen magnum and occipital condyles) and structures from the anterior tip of the rostrum (e.g., P. tricuspis). Nevertheless, the modular architecture retrieved for the best sampled species could be associated to functional/developmental modules defined in previous studies (Goswami, 2006).

For brevity, we here describe in detail the architecture for the two best sampled species only. We recovered a six-module architecture for P. tricuspis, with landmarks corresponding to the basicranium, the vault, the orbit (limited to the alisphenoid), the molar-palate region, the zygomatic arch, and the oro-nasal/rostrum region (Figs. 2A). Similar to other species, P. tricuspis presented landmarks from the occipital condyles grouped with the rostrum cluster. In Tamandua tetradactyla, the six-module architecture was the most frequently found in the network analysis (Fig. 2), but only four of these clusters corresponded to morphofunctional regions, i.e. the basicranium, orbit, vault, and oro-nasal/rostrum. Contrary to P. tricuspis, the landmarks from palatine/molar cranial and anterior zygomatic regions were grouped with the oronasal/rostrum module. The most anterodorsal projection of the zygomatic process of the squamosal was grouped with landmarks from the orbital region. The landmarks placed on the infraorbital foramina (#3/23) formed a two-landmark cluster. The sphenopalatine and caudal palatine foramina (#6/25 and #7/26) formed a separated cluster from the rostrum (Fig. 2), but still strongly connected to it, so these two groups were subsequently treated as a single module.

We ran the MCN procedure on a randomly selected subset of P. tricuspis specimens (n = 36) to test the sensitivity of this method to reduced sample sizes. We obtained a different configuration consisting of four models (Fig. 2a) with landmarks from different modules grouping together instead of presenting a similar structure to the full dataset analysis. These clusters consisted of groupings including merged landmarks from the anterior zygomatic, molar-palate, and oro-nasal modules (face/rostrum) and three

Exploratory analyses of modularity -EDMA

Manis crassicaudata (n = 7) and Otocyon megalotis (n =8) were the least sampled species in this study.

The modular structures resulting from EDMA were not well-defined in these two species, with clusters including landmarks distributed heterogeneously in the skull. The Gap test revealed that the skull was optimally divided between 3 and 9 clusters, with the exception of Smutsia gigantea and Orycteropus afer, which were considered to optimally consist of one single cluster. In these cases, we arbitrarily divided the skull in five modules. A high number of clusters was often associated to grouping of two bilaterally symmetric landmarks, and in some cases bilaterally symmetric clusters (e.g., the molar/zygomatic regions of Proteles cristatus). For each species, we reduced the number of clusters to the point to which no cluster was formed by single or bilaterally symmetric landmarks only. Concerning the division of the skull, the oro-nasal and the basicranium regions were well-preserved across all taxa. The oro-nasal was composed by the landmarks at the anterior parts of the maxilla and nasal in all species. The basicranium included the landmarks of the occipital region (basioccipital, exoccipital, and the supraoccipital). In Tamandua spp.

and Cyclopes didactylus (Fig. S2), the most posterior cluster was restricted to the occipital region.

However, the basicranium was in the same module as the landmarks of the midline of the cranial vault and the anterior margin of the tympanic ring in pangolins (Fig. S2). In P. tricuspus, the intersection between interfrontal and interparietal sutures is excluded from the basicranium/tympanic ring cluster. In S. gigantea, P. tetradactyla, and M. pentadactyla this cluster also included the zygomatic processes of the squamosal (Fig. S3). O. afer showed a cluster including the occipital region associated to the posteriormost point of the interparietal suture. Priodontes maximus showed a similar cluster to that of O. afer, with the anterior margin of the tympanic bulla (Fig. S3).

The other parts of the skull were, however, much less conserved across the species (Fig. S2-3).

The middle part of the skull presented two main clusters, one including the pterygoid region (#12/30, #13/31, #14/32) and landmarks from the vault (#43 and sometimes #44), and another consisting of the molar-palate regions. The landmarks of the orbit region were often split between the pterygoid and the molar-palate modules, with a few exceptions in which it formed an independent cluster (e.g., T. mexicana and S. gigantea).

The naso-frontal/maxilla-palatine interaction region presented different partitions among myrmecophagous placentals. These differences were related to the landmarks at the posterior part of the nasals (#39/50, #42) and the infraorbital foramen (#3/23). In most species these landmarks clustered together with points located more posteriorly, as the maxillary foramen (#4/24), the palatine foramina (#6/25, #7/26), the point between the interpalatine-intermaxilla sutures (#5), and the zygomatic processes of the maxilla (#41/52). However, in T. tetradactyla, T. mexicana, and O. afer, the landmarks at the nasalfrontal interaction and those at the level of the maxilla-palatine suture clustered separately from the others (Fig. S2-3). In P. maximus and M. tridactyla, the intermaxilla-interpalatine point or the infraorbital foramen were excluded from this naso-palatine cluster, respectively. Additionally, in P. tetradactyla, the landmarks on the posterior part of the nasal formed a small cluster.

A priori modular architecture hypothesis testing

The results of the modular architecture selection by maximum-likelihood (EMMLi) including all a priori hypotheses and those modified based on EDMA and obtained from MCN analyses (Tables 123).

In the MCN-architectures obtained for P. tricuspis (VII), the occipital condyles landmarks were reallocated to the basicranium. Before correcting data for static allometry, EMMLi retrieved a seven-module architecture (eight of which, architecture IX) for nine species. Five species (P. tricuspis, S. gigantea, S.

temminckii, M. pentadactyla, and P. cristatus) showed a six-module architecture, and one species (M. crassicaudata) was found to present a three-module architecture. In the case of M. crassicaudata and P.

maximus, the most likely architecture presented a posterior probability below 50%. In O. megalotis, the most likely architecture presented a posterior probability of 80%, but three other architectures showed at least 5% (Table S3). Static allometry was detected for all species, except P. maximus, M. crassicaudata¸ P. cristatus, and O. megalotis. Apart from these species, results reported herein relate to the allometrycorrected data (Table 3). Static allometry did not affect the number of retrieved modules except in M javanica, which presented a four-module architecture (III) after allometry correction (Table 3).

Allometric-correction also changed the modular architecture of O. afer, P. tetradactyla, and S. temminckii, but without changing the number of modules. Landmark changes occurred in the zygomatic-pterygoid and nasal-frontal regions (S. temminckii; Table 3). Of the eleven species for which static allometry was a significant component of skull shape, allometry-corrected skulls presented a seven-module architecture in six species. Four species presented a six-module architecture and only one presented a four-module architecture.

All anteaters, P. tetradactyla, P. maximus, and O. megalotis presented architecture IX (Table 3).

This consists of the six functional modules (Goswami, 2006) with an additional naso-palatine module derived from the EDMA analyses. In P. tetradactyla, the posterior probability for architecture IX was just 42%, with III, V, VI, and VII showing probabilities between 10-20% (Table S4). O. afer, presented the VII, in which landmarks for the orbit module are restricted to the orbitosphenoid/alisphenoid complex. C. didactylus showed the least integrated orbit (ρ = 0.21; Table 3). andO. afer, the naso-palatine module was more strongly integrated with the oro-nasal than within itself (Table 4). 2 and3). Null values indicate either the absence of a module in the respective species or the inexistence of allometry in the sample.

When the absolute correlations between the oro-nasal and molar/palatine regions were considered, they were more negative in specimens with a longer rostrum (Tables 2 and3). P. cristatus, O. megalotis, and M. crassicaudata presented the less negative correlations (ρ < -0.13), while S. gigantea, Tamandua spp., and M. tridactyla showed more negative values (-0.31 ≥ ρ ≥ 0.45). Non-corrected values showed a similar pattern, but this analysis showed that these negative correlations were partially a result of static allometry in M. tridactyla and S. gigantea (Table 3). The PLS analyses between independently aligned modules of the two most sampled species revealed that covariation was not significant between all modules (Tables S5 andS6). In P. tricuspis, less than half of the inter-module correlations were significant after adjusting the p-values for multiple comparisons. The oro-nasal/dorsal rostrum region showed a marginally non-significant correlation with the molar-palate module (p = 0.06). The molar-palate module was significantly correlated with the small orbit, the zygomatic-pterygoid, and the basicranium. The orbit significantly correlated with the zygomaticpterygoid and the vault, while the latter presented a significant correlation with the vault. In T. tetradactyla none of the four modules recovered with the MCN analysis significantly correlated with each other, after adjusting for multiple comparisons. Before the adjustment of the p-values, the correlation between the rostrum and the zygomatic pterygoid was marginally significant. In both species, PLS performed between modules from a common Procrustes superimposition showed an increase in the number of significant correlations (Tables S5 andS6). In P. tricuspis, all but one correlation were highly significant (oro-nasal+molar-palate was marginally significant; p = 0.4), while T. tetradactyla presented a non-significant zygomatic-pterygoid+vault (p = 0.10) and a marginally significant oro-nasal+vault (p = 0.04) correlations.

Both P. tricuspis and T. tetradactyla modular integration changed substantially when separate Procrustes superimpositions were performed per module (Table S5 andS6). In P. tricuspis, the integrations of the oro-nasal, orbit/alisphenoid slightly decreased, those of the molar-palate, zygomatic-pterygoid, and vault increased, while that of the basicranium remained unchanged (Table S5). In T. tetradactyla, only the vault became more integrated when aligned separately. The remaining modules presented decreased integrations, when compared to those measured from a single Procrustes superimposition (Table S6). The integration of the rostrum and the basicranium decreased by more than 50%.

Evolutionary modularity

The Procrustes ANOVA reveals a weak (R 2 = 0.07) but marginally significant effect of size on skull shape (F1,34 = 2.37; p = 0.04). The principal component analyses on the residuals of this regression showed that, despite the phylogenetic affinities, the different skull morphologies clearly separated anteaters from their sister taxa armadillos and sloths, as well as pangolins from carnivores. Most of the skull shape variation (90%) is explained by the first seven principal components (PCs). PC1 explains 39.64% of the variance and mainly explained the degree of anterior projection of the nasal bones relative to both frontal bone and the anterior most part of the maxillae, the distance between the maxillary and squamosal zygomatic processes, and the width of the rostrum (Fig. 4). Ferae species (Carnivora + Pholidota) present mostly EMMLi recovered the seven-module naso-palatine (X; derived from Hallgrimsson et al., 2004) architecture to be the most likely architecture for our interspecific dataset, both when using correlations matrices derived from raw shape coordinates and allometry-corrected shapes (Table 5). The oronasal/rostrum module was strongly integrated (ρ = 0.66/0.68) and showed the highest inter-modular correlation with the palate/molar module (ρ = 0.53/0.54). The oro-nasal/rostrum was also well correlated with the orbit (ρ = 0.47/0.48). The molar-palate was the most integrated of all modules (ρ = 0.78/0.78), with the orbit (ρ = 0.41), the zygomatic (ρ = 0.21/0.22), and the vault (ρ = 0.27/0.28) showing the lowest values (Table 5). The basicranium was also strongly integrated (ρ = 0.48/0.52), although less than the two modules of the rostrum. The CR test found the modular architecture X to be significant for both raw shape coordinates (CR = 0.85; p = 0.001) and allometry-corrected shapes (CR = 0.84; p = 0.001) datasets. Table 5 -Within-and between-modules correlations from the most likely (Hallgrimsson 7) modular architecture for 15 myrmecophagous and 21 non-myrmecophagous species. (1) Oro-nasal/rostrum, (2) molar-palate, (3) orbit, (4) pterygoid, ( 5) vault, ( 6) basicranium, ( 7) naso-palatine. Respective within-module correlations (ρ) for raw shape coordinates and allometry-corrected shapes are in bold. Between-module correlations output from EMMLi in the upper (allometry-corrected coordinates) and lower (raw shape coordinates) triangles. Evolutionary rates were assessed for allometry-corrected skull shapes only. The measurement of skull shape evolutionary rates for the face-neurocranium two-module architecture revealed that the rostrum/face tend to faster than the neurocranium (Table 6). Anteaters were the clade that showed the highest evolutionary rates for the rostrum/face, while pangolins showed one of the lowest (the lowest if we exclude single-membered groups as Marsupials and Euarchantoglires; Fig. 5A, Table 6). Within anteaters, M. tridactyla and C. didactylus showed the faster rates, while these decrease in the genus Tamandua, when compared to the sister taxon within the Myrmecophagidae. In pangolins, the branches leading to Phataginus spp., M. pentadactyla, and M. crassicaudata exhibit the slowest morphological evolutionary rates, alongside U. arctos. Rostrum/face shape increases in the branches leading to Smutsia spp., particularly the large bodied S. gigantea. Within the genus Manis¸ the branch leading to M. javanica

shows a slightly faster evolutionary rate. Xenarthrans showed relatively fast evolving rostra/faces when compared to those of other clades (Fig. 5A). Within Xenarthra, Tamandua showed slowly changing neurocrania/basicrania (Fig. 5B). The comparison of the evolutionary rates between myrmecophagous and non-myrmecophagous mammals did not yield a significant difference, both when comparing the rostrum/face, or the neurocranium/basicranium (Tables 6). When toothless species and respective sister taxa were split into separate groups (Pholidota vs Carnivora; Vermilingua vs Atlantogenata), the pairwise comparisons showed that the rostrum/face of anteaters showed a significantly faster evolutionary rate than that of pangolins and carnivores (Table 5).

The same test revealed a close to significance (p = 0.07) difference between the evolutionary rate of the anteater rostrum compared to that of the remaining Atlantogenata. Concerning the neurocranium/basicranium, the shape in anteaters evolved marginally faster than that of pangolins (Table 6). Comparisons with Carnivora and the sister-taxa within Atlantogenata did not yield significant rate differences. Evolutionary rates for the individual rostrum modules presented similar patterns to those obtained for the full rostrum module. Therefore, in order to avoid a redundant comparison, we present the results in a graphical way only (Fig. S5). The module naso-palatine module was not represented, as its validation as an independent module is uncertain (see 'Discussion').

Comparison of covariance matrices

The PCA performed on the Procrustes aligned coordinates of the full dataset revealed that 90% of the variance was explained by the first seven PCs. These axes were retained for all posterior analyses. The PCoA performed on the 15-species Euclidean distance matrix showed that 90% of the variance was explained by the first five coordinates (Cos) of the multidimensional space. Co1 (42.1%; Fig. 6A) shows a trend from toothed (negative values) to toothless and long-snouted (positive values) species. P. cristatus presents the lowest Co1 value, while M. tridactyla presents the highest. Co2 (26.1%; Fig. 6A) mostly segregates S. temminckii (outlier with high positive values), T. tetradactyla, S. gigantea, and M. tridactyla from all the remaining species. M. tridactyla presents the most negative Co2 value, followed by T.

tetradactyla and S. gigantea with values relatively closer to the cluster including most of the species on the middle-left side of the morphospace (Fig. 6). Cos 3 (9.0%; Fig. 6B) and 4 (7.0%) do not appear to show an identifiable biological signal associated to the covariation patterns.

The PCA performed on the Procrustes aligned coordinates of P. tricuspis (including juveniles) revealed that 90% of the variance in skull shape was distributed in the first 25 axes of the morphospace.

The PCoA performed on the resultant distance matrix including four age/size groups revealed that the relationship between phenotypic covariance and size is not linear during the ontogeny in P. tricuspis (Fig. 7A,B). The analysis performed on the distance matrix for the T. tetradactyla dataset (24 PCs) revealed a similar result, although the trajectory was different (Fig. 7C,D). In both cases, stage 1 is separated from the remaining ones by Co1, with later stages being separated by Co2.

Discussion

Exploratory analysis of modularity

Exploratory methods are a good complement to a priori hypothesis testing, as they may reveal patterns that are not predicted in a priori developmental, functional, or even physiological hypotheses (Zelditch et al., 2008). We applied, for the first time, the morphological correlation networks methodology (MCN, Suzuki, 2013) to assess the modular patterns of the mammalian skull. Our results show that, for most species, the clusters recovered from the network analyses did not deliver a fine grouping of functional modules (Goswami, 2006).

Some of the illogical and gross clusters found might result from methodological biases. Typically, landmarks from the oro-nasal region were often found to cluster with basicranial structures (Fig. 2A). This particular case might be related to covariance introduced by the Procrustes superimposition (see 'Procrustes superimposition in integration and modularity').

Nevertheless, the networks resulting from our most sampled species P. tricuspis (n=72) and T.

tetradactyla (n = 74) retrieved modular patterns resembling those found in previous studies (Cheverud, 1982;Goswami, 2006). While this could be related to a strong modular structure of the skull for these two species, MCN might also be sensitive to the number of sampled individuals (Fig. 2a). Anatomically, the modular pattern retrieved from the MCN performed on P. tricuspis and T. tetradactyla showed a clear differentiation between these two species, mainly at the level of the division of the rostrum and palate and the structures of the orbit and zygomatic-pterygoid. Goswami (2006), Cheverud (1982), and Parr et al. (2016) found an individualized orbit module that includes the anterodorsal part of the orbit and the border region between the nasal and frontal bones.

In the MCN-derived P. tricuspis architecture, the orbit module is much smaller and consists of the ali-and orbitosphenoid. As for the dog (Parr et al., 2016), the zygomatic and pterygoid regions are not included in the same module in P. tricuspis. In both cases, a zygomatic arch module was recovered. The MCNderived modular architecture for P. tricuspis also revealed a change in the covariation patterns within the rostrum (Fig. 1B). While the posteroventral part of the rostrum follows a similar pattern to that of other mammals, landmarks from the oro-nasal and the fronto-nasal regions are included in a single module, which contrasts with the condition seen in dogs (Parr et al., 2016), rhesus macaques (Cheverud, 1982), and the therian six-module pattern (Goswami, 2006).

Contrary to P. tricuspis, T. tetradactyla showed a four-module architecture. The absence of an orbit module sensu Goswami (2006) in T. tetradactyla is similar to the condition in P. tricuspis. However, T. tetradactyla exhibited integrated oro-nasal and molar regions, while these were grouped independently in P. tricuspis. Contrary to P. tricuspis, the naso-frontal region of T. tetradactyla is integrated with the landmarks of the vault module. This might be explained by a more pronounced projection of the anterior flanges of the frontal bone, associated with the facial process outgrowth (Hallgrímsson et al., 2007(Hallgrímsson et al., , 2009)).

The zygomatic-pterygoid module of T. tetradactyla corresponds to the one defined by Goswami (2006) plus the ali-and orbitosphenoid orbit foramina. It is restricted to the posterior part of the skull, as neither the zygomatic process of the maxilla nor the highest point of the maxilla-palatine suture are included in this module (opposite to P. tricuspis). Landmarks corresponding to the midline of the palatines-maxillae suture and the infraorbital foramen were separated from all other clusters. This might represent a shift associated to either rostrum elongation or tooth loss, resulting in a dissociation from the molar-palate.

Contrary to MCN, the EDMA procedure does not require landmarks to be aligned with Procrustes superimposition. This avoids the issues related to estimations of variability of the landmarks that are placed further from the centroid of shape [START_REF] Lele | An invariant approach to statistical analysis of shapes[END_REF]. Although the number of clusters is not straightforward to determine [START_REF] Jung | A decision criterion for the optimal number of clusters in hierarchical clustering[END_REF][START_REF] Salvador | Determining the number of clusters/segments in hierarchical clustering/segmentation algorithms[END_REF][START_REF] Kassambara | Practical guide to cluster analysis in R : unsupervised machine learning[END_REF], hierarchical clustering is useful in detecting potential modules when the general organization of a structure is unknown (Cheverud, 1982;[START_REF] Lele | Euclidean distance matrix analysis: A coordinate-free approach for comparing biological shapes using landmark data[END_REF]Goswami, 2006). The visual comparison of modular patterns recovered from our species allowed us to notice that the landmarks from the nasopalatine region tended to cluster apart from our a priori defined molar-palate module. This was particularly evident in T. tetradactyla, in which these landmarks clustered separately from the rest of the skull (Fig. S2A). In T. mexicana, M. tridactyla and O. afer the naso-frontal and maxilla-palatine landmarks were also separated from the orbit and molar-palate regions, respectively. These landmarks appear to represent a decoupling of naso-palatine landmarks that could be related to skull elongation or to the release from constraints associated to tooth eruption in anteaters (Mitteroecker & Bookstein, 2009;[START_REF] Klingenberg | Development of the mouse mandible: a model system for complex morphological structures[END_REF]. However, this decoupling was not as evident in other myrmecophagous species, such as pangolins or the aardwolf. This result could indicate structural constraints associated to phylogenetic relatedness, given that both groups are sister taxa (Murphy et al., 2001a). It could also suggest the relaxation of phylogenetic constraints in anteaters and aardvarks.

Procrustes superimposition in integration and modularity

Recently, Cardini (2019b) alerted for the risk of spurious results in analyses of integration and modularity using a single Procrustes analysis to superimpose landmark coordinate datasets. The author demonstrated that undesirable covariation is introduced during the process of alignment, rotation, and scaling. The covariation introduced by the Procrustes superimposition may create modular structures in non-modular datasets (Cardini, 2019b). In the same time, performing separate Procrustes superimpositions per module may also remove a biologically relevant part of the covariance, especially the one relative to size and orientation of the modules (Klingenberg, 2009b;Cardini, 2019b). Given that somatic growth and resulting allometric signal are the dominant promoters of integration (Hallgrímsson et al., 2007;Porto et al., 2009), this can be problematic in the case of myrmecophagous mammals, in which rostrum growth is an important variance generator.

Our results are in line with those of Cardini (2019b), showing that some correlations between modules are created by Procrustes superimposition (Tables S5 andS6). For instance, our partial leastsquares (PLS) analyses between separately superimposed modules in P. tricuspis showed that the oronasal and basicranium regions (associated in the MCN) do not significantly covary (Table S5 andS6).

Procrustes superimposition also appears to have an important effect in the magnitude of integration, as shown by our comparisons between single and separated Procrustes superimposition. In general, intramodule correlations present more similar values when Procrustes superimpositions are performed by module than when a single Procrustes is performed for the whole skull.

or occlusion (Hallgrímsson et al., 2007(Hallgrímsson et al., , 2009[START_REF] Hallgrímsson | Integration and the developmental genetics of allometry[END_REF][START_REF] Bookstein | Comparing covariance matrices by relative eigenanalysis, with applications to organismal biology[END_REF] mostly occur anterior to the temporal fossa.

In contrast, we showed that the anterior half of the skull shows more parcellation, as previously suggested in mammals (Cheverud, 1982;Goswami, 2006;Porto et al., 2009;[START_REF] Makedonska | The effect of dietary adaption on cranial morphological integration in capuchins (Order Primates, Genus Cebus) (S Gursky-Doyen[END_REF]Parr et al., 2016). Nevertheless, we found relatively conserved modular patterns among myrmecophagous species. Most presented the same seven-module architecture derived from Goswami ( 2006) functional hypothesis with the addition of a naso-palatine module as suggested by the EDMA hierarchical clusters. However, this result largely contrasts with the MCN result for Tamandua tetradactyla. One possible explanation could be that EMMLi favours architectures with larger numbers of modules compared to models with fewer partitions (e.g., Felice & Goswami, 2018;Bardua et al., 2019).

When the seven-module architectures were removed from the EMMLi tests, both Tamandua spp.

presented the model corresponding to that obtained from the MCN of T. tetradactyla (III; Table S7). A look at the correlations between modules shows that the naso-palatine module is more strongly correlated with the oro-nasal module than within itself (Table 4). Theoretically, a phenotypic module should share stronger interactions within it than with the surrounding elements of the system (Klingenberg, 2005).

Therefore, oro-nasal and naso-palatine could potentially represent a single module in Tamandua spp (Table 4). MCN and EMMLi results do not, however, invalidate each other. As revealed by EMMLi, the oro-nasal and the molar-palate are well-integrated in T. tetradactyla (ρ = 0.43), which is in line with the single rostrum module retrieved by the MCN. On the other hand, the landmarks of the nasal-frontal suture might simply be more correlated with the anterior part of the cranial vault (frontal bone) than with the oronasal, which would justify its coupling with the cranial vault in the MCN.

Overall, modular architectures in Tamandua spp./M. tridactyla (both MCN-and EDMA-derived), and most pangolins (MCN-derived) appear to suggest a trend for rostrum integration, which might translate the preservation of covariance generated early in ontogeny (orofacial region; Zelditch & Carmichael, 1989), with a reduction of parcellation associated to tooth eruption and functional musclebone interaction normally linked to later developmental stages (Herring, 1993;Hallgrímsson et al., 2007;Mitteroecker & Bookstein, 2009).

Modularity and the evolution of myrmecophagy Despite some differences detected among myrmecophagous placentals, the modularity patterns were comparable to those found in previous studies including mammals (Cheverud, 1982;Goswami, All pangolins are toothless and unable to chew (Endo et al., 1998). The presence of a zygomatic module is better explained by the strong ontogenetic allometric trend towards the growth of the zygomatic process of the maxilla reported in pangolins (Ferreira-Cardoso et al., 2019a). [START_REF] Porto | Size variation, growth strategies, and the evolution of modularity in the mammalian skull[END_REF] found the zygomatic module to be absent in several mammalian groups with chewing and biting ability, which suggests a decoupling between masticatory function and the presence of a zygomatic arch module.

In the two species for which we had juvenile specimens (P. tricuspis and T. tetradactyla) we showed that, although missing the early stages of post-natal development, the covariance structure of the skull is changing throughout ontogeny ( Fig 7). On the light of the 'Palimpsest model', modules derive from developmental processes with the potential to generate coordinated variation during skull ontogeny (Hallgrímsson et al., 2007(Hallgrímsson et al., , 2009)). These processes, such as neural crest migration (embryonic variation)

or brain growth, all introduce variation at a certain stage, with the static phenotypic covariance patterns being a result of the overlap of several determinants of covariation (Hallgrímsson et al., 2007(Hallgrímsson et al., , 2009)).

Specific determinants of covariation (e.g., masticatory function) might therefore be hard to infer from static modularity patterns [START_REF] Fischer-Rousseau | Morphological integration and developmental 195 progress during fish ontogeny in two contrasting habitats[END_REF].

Overall, the modular architectures recovered for the myrmecophagous species appeared to reflect a slight change in covariation patterns in the anterior half of the skull. In some species, tooth loss and snout elongation may have contributed for a less modular rostrum. Additionally, the masseter musculature and the structure of the zygomatic arch appear to be reflected in a quite inconstant composition of the zygomatic-pterygoid module. Namely, there appears to be a tendency for species without a functional zygomatic arch to maintain only the posterior part of this module preserved, but this is hardly related to function. The variability of modular structures in anteating mammals is particularly evident when comparing the phenotypic covariance matrices (PCoA), with toothed species occupying a much less dispersed in the morphospace. We also showed that significant differences on shape (e.g., C. didactylus vs M. tridactyla) do not necessarily translate into different modularity patterns, as an increase in variance on a few axes might reflect in very distinct morphologies due to pleiotropic effects.

Morphological integration and allometry

Previous studies showed that both within-modules and total integration vary across taxa (Goswami, 2006;Porto et al., 2009;Goswami & Polly, 2010;Randau et al., 2019). As in other mammal clades (e.g., Goswami, 2006;Porto et al., 2009), the oro-nasal module of myrmecophagous species is more integrated than the remaining ones, with some taxa showing a moderately integrated basicranium.

The stronger integration of the oro-nasal module is explained by ontogenetic allometry and represents a pattern common to all mammals [START_REF] Cardini | Larger mammals have longer faces because of size-related constraints on skull form[END_REF]Cardini, 2019a). In the context of myrmecophagy, extreme rostrum elongation was reflected by the negative correlation between the oronasal and the molar-palate modules (sensu Goswami, 2006). These correlations were more negative in M.

tridactyla and the two Tamandua compared to all the remaining species. On the opposite pole, P. cristatus and O. megalotis presented the less negative correlations. A negative correlation suggests a strong ontogenetic allometric effect on the rostrum region, reflecting the opposite directions of variation in its anterior and posterior parts (e.g., Ferreira-Cardoso et al., 2019a). The best examples of this trend are M.

tridactyla, Tamandua spp., and S. gigantea. Additionally, in the largest anteater and pangolin species (M. tridactyla and S. gigantea) a significant part of these negative correlations is associated with static allometry (Tables 2 and3).

Our results also show that overall integration increases with size. M. tridactyla and S. gigantea are the largest species within anteaters and pangolins, respectively. Overall, all their modules are much more integrated than in their sister species (Tables 2 and3). This can be explained by the covariation generated by the overall size increase of the skull and thus influencing all traits in the sample [START_REF] Nijhout | Dependence of morphometric allometries on the growth kinetics of body parts[END_REF].

Nevertheless, in M. tridactyla and S. gigantea, static allometry appears to be responsible for a good part of the integration, given that in general its values dropped after allometric correction (particularly those of the oro-nasal ragion). On the other hand, in Tamandua spp. show similar integration values after accounting for static allometry, which could indicate that most of the covariance was generated before adulthood (Table 3). For example, judging from the elongated shape of the rostra of anteaters fetuses (Fig. 1C; [START_REF] Hautier | Skeletal ossification and sequence heterochrony in xenarthran evolution[END_REF], it is likely that a significant part of the somatic growth behind the increase in the integration of the rostrum regions (mainly oro-nasal) occurs during pre-natal development (Zelditch & Carmichael, 1989). Nevertheless, our phenotypic covariance trajectories (Fig. 7) show that changes may still occur in covariance/correlation matrices during post-natal development (Fig. 7).

We confirm that size variation is an important factor influencing integration magnitude in the mammal skull. While this was previously shown to be an evolutionary trend among placentals [START_REF] Cardini | Larger mammals have longer faces because of size-related constraints on skull form[END_REF][START_REF] Porto | Size variation, growth strategies, and the evolution of modularity in the mammalian skull[END_REF]Cardini, 2019a), our intraspecific analysis shows how canalized cranial variation is in placentals. In this case, selective pressures associated to myrmecophagy triggered a phenotypic response along axes of variation that are very conserved at the evolutionary level. This response might have been facilitated by complete tooth loss. Although early stages of tooth development occur in anteaters (Gervais, 1867;Rose, 1892), osteogenesis associated to that process (e.g., trabecular bone) is much reduced (Ferreira-Cardoso et al., 2019b). Therefore, the reduction of covariance introduced by tooth development might have released the naso-palatine module to co-vary more with the oro-nasal region (e.g., anteaters). This might explain why covariance matrices are more conserved within toothed myrmecophagous placentals when compared to the toothless ones (Fig. 6). Although the long-snouted S.

gigantea appears to have a conserved molar-palate module, the inclusion of the naso-frontal landmarks in the oro-nasal module might also have a similar explanation.

Rates of morphological evolution

We showed that myrmecophagous mammals present a morphological convergence in the morphospace (Fig. 4). Our results also show that this convergence did not result from the convergence of the rates of morphological evolution. Instead, we found that the evolution of the morphology of the anteater rostrum is a result of high morphological evolutionary rates compared not only to its sister taxa but also to the remaining species included in the analyses (Fig. 5; Table 6). Surprisingly, the equally toothless pangolins showed a completely opposed scenario, showing very low rates of morphological evolution. While the high rates of morphological evolution could explain the average high integration of the rostrum and oronasal regions compared to the other modules within anteaters, it does not explain the shift of pangolins in the morphospace, when compared to their carnivoran sister taxa (Murphy et al., 2001b,a). The relatively low evolutionary rates might be explained by the absence of recently diverged sister taxa to pangolins, and probably reflects a sampling/methodology bias. The addition of a toothed sister taxon to pangolins, like the palaeanodonts [START_REF] Emry | A North American Oligocene pangolin and other additions to the Pholidota[END_REF]Gaudin, Emry, & Wible, 2009) could help in the better estimating the shape of the pangolin ancestor, therefore enabling a better estimation of the evolutionary history of skull morphology in this group. On the other hand, the morphospace occupied by anteaters extends much more than that occupied by pangolins, as well as the distance from their sister group, the sloths (Fig. 4).

Although a larger sampling at the placental scale would be needed and different models of evolution (e.g., Ornstein-Uhlenbeck, Early Burst; [START_REF] Harmon | GEIGER: investigating evolutionary radiations[END_REF][START_REF] Alfaro | Nine exceptional radiations plus high turnover explain species diversity in jawed vertebrates[END_REF], our results suggest that the ecological convergence towards myrmecophagy did not involve the same degree of evolutionary rates of the rostra modules in anteaters, pangolins, and the remaining ant-eating placentals.

Conclusion

We showed that morphological changes in ant-and termite-eating lineages did not radically change the modular patterns in myrmecophagous placentals. Considering phenotypic correlations and covariances as

4-Conclusion and perspectives

The background for this thesis was carved in the early 19 th century by Étienne Geoffroy Saint-Hilaire and Georges Cuvier. The concepts of structural and topological constraint, associated to the correlation of forms with the environment have since been given many definitions, and several manners to quantify it have been developed. Today, in the light of Darwin and Wallace's theory [START_REF] Darwin | On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection[END_REF][START_REF]On the origin of species by means of natural selection or the preservation of favoured races in the struggle for life[END_REF] and a rather stable phylogenetic context, the goal of this work was to explore convergent evolution, in the context of strong dietary selective pressures applied to a complex system, the placental skull. Along the way, I tried to understand the multiple factors behind skull shape variation both at a broad phylogenetic scale (myrmecophagous mammals) and in a more evolutionary constrained context (pangolins).

In the first chapter of this thesis, I went on to answer to explore skull shape variation among pangolins species, the most heavily poached mammal on Earth. Using geometric morphometrics, I was able to show that seven of the eight extant species of pangolins display very distinct skull shapes. If classifications based on morphology (Gaudin, Emry, & Wible, 2009) and genetics (Gaubert et al., 2018) are mostly congruent, the major generator of skull shape variance among mammals (allometry) can introduce noise and flawed conclusions based on phenetics. In particular, I showed how heterochrony within a single genus has the ability to play a strong role in cranial shape differentiation, and how such differentiation is mostly ruled by different allometric patterns between well-defined face/rostrum and the neurocranium modules [START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF]. The second aspect of the first chapter consisted in exploiting the concept of cryptic species [START_REF] Bickford | Cryptic species as a window on diversity and conservation[END_REF] by assessing the potential of skull shape to delimitate molecularly divergent lineages [START_REF] Gaubert | Phylogeography of the heavily poached African common pangolin (Pholidota, Manis tricuspis ) reveals six cryptic lineages as traceable signatures of Pleistocene diversification[END_REF]. This chapter evokes several aspects of morphological variation and exemplifies the role played by ontogenetic allometry in skeletal shape. It also took a glimpse on the morphological differentiation during speciation, and presents an example of a decoupling between genetic and morphological divergence in a recent cladogenesis event [START_REF] Bickford | Cryptic species as a window on diversity and conservation[END_REF].

In the second chapter of this thesis, convergent evolution was dissected, literally (Article 3) and conceptually, on the basis of comparative anatomy. The convergent evolution of myrmecophagy allowed for testing the strict evolutionary repeatability in the case of phylogenetically distant organisms. Ant-and termite-eating can be considered a "natural experiment" in which genetically and morphologically different populations were exposed, during millions of years, to similar conditions. In the first part of the chapter, the comparison of the internal anatomy of the mandible at the scale of placentals showed that external convergence (i.e., tooth loss) was not corresponded by convergent internal features (i.e., maintenance of tooth innervation/irrigation) in anteaters and pangolins. This suggests that the anteaterpangolin example is indeed a case of true convergence (McGhee, 2011), as toothlessness evolved through different processes in the two clades. In other words, differences in mandibular innervation/irrigation patterns might have resulted from distinct timings/mechanisms of odontogenesis interruption. This example is in line with the existence of multiple pathways of evolution in response to one specific selective pressure [START_REF] Bock | Preadaptation and multiple evolutionary pathways[END_REF]. In reverse, my study suggests that odontogenesis is rather conserved across mammals, assuming a correlation between similar the phenotypes in anteaters and toothless whales and their development. Conway Morris' view that evolution would happen the same way, were it to be repeated again and again, is based on the idea that there is a restricted number of solutions available to life. The anteater-mysticete example is congruent with this view, and conforms to the idea that life is limited to a theoretical morphospace [START_REF] Mcghee | Theoretical morphology: the concept and its applications[END_REF]. The explanation behind these apparently contradicting examples might be explained by slightly different functions performed by the mandibles of pangolins, anteaters, and mysticetes, which could demand a more developed sensorial system in the latter two groups.

In the second parts of the chapter 2, the comparison between head musculatures of the three living anteater genera showed how hypothetically similar functional systems may present distinct morphologies. This is the very concept of many-to-one-mapping as defined by Wainwright et al. (2005). Adaptive evolution may respond differently to identical selective pressures, ultimately resulting in a multitude of equally optimal responses [START_REF] Bock | Preadaptation and multiple evolutionary pathways[END_REF]. While this research is limited by its qualitative nature, it paves the way to future studies on the biomechanics on the feeding apparatus of ant-and termite-eating placentals, as it stresses the need for performance testing. In line with the first article of the chapter 2, the comparison of the head musculature in anteaters with previous descriptions of those of pangolins and aardvarks allowed to trace the limits of convergence, as some key differences are observed between these three distantly related clades.

Lastly, the third chapter of this thesis focused on the patterns of phenotypic covariance in the skull of myrmecophagous species. The results showed that despite the morphological differences characterizing these species, the modular patterns were conserved. I failed to associate loss of function (i.e., mastication)

with the covariance patterns of the skull. The genetic and developmental basis of the placental skull are extremely conserved, hindering drastic changes in modularity patterns even under strong selective pressures (canalization). Under this scenario, limited axes of variation are available for the phenotype, with morphological changes happening through changes in integration within conserved phenotypic organizational modules [START_REF] Cardini | Larger mammals have longer faces because of size-related constraints on skull form[END_REF][START_REF] Parsons | Conserved but flexible modularity in the zebrafish skull: implications for craniofacial evolvability[END_REF]Felice et al., 2019). This study points instead to an apparent conservation patterns associated to early ontogeny (i.e., facial growth) that could be associated to both the absence of tooth eruption and to the pronounced allometric growth of the rostrum (e.g., myrmecophagid anteaters).

This thesis tried to provide an integrative approach to cranial morphological variation, including a set of different geometric morphometrics and comparative anatomy techniques, while taking advantage of the increasing availability of µ-CT scanning and its combination with contrast-enhanced methods for reconstruction of soft-tissues. I tried to use these methods to give new insights on the systematics, allometric patterns, tooth loss, muscular anatomy, and phenotypic covariance patterns among the convergently evolved myrmecophagous placentals. There are, however, several subjects that remain to be studied.

As in the first chapter, similar approaches should be used to explore the phenotypic variation and allometric patterns among anteaters, especially the genus Tamandua. Variation between populations of Tamandua tetradactyla and differences between this species and its sister taxon, T. mexicana, would benefit from a re-evaluation with modern geometric morphometric methods in comparison to molecular datasets. This would allow to revive the interest on geographical phenotypic variation in these species and add up to previous works covering systematics [START_REF] Reeve | A statistical analysis of taxonomic differences within the genus Tamandua Gray (Xenarthra)[END_REF]Wetzel, 1975) and allometric patterns [START_REF] Reeve | Relative growth in the snout of anteaters. A study in the application of quantitative methods to systematica[END_REF] of the Vermilingua. Most importantly, it could provide essential knowledge with direct application in conservation, such as the identification of potential management units [START_REF] Palsbøll | Identification of management units using population genetic data[END_REF]Hautier et al., 2014;Ferreira-Cardoso et al., 2019a).

The investigation of patterns of mandibular innervation in myrmecophagous placentals opened several questions related the mechanism behind the ondontogenesis interruption in toothless mammals.

The methodology used in the Article 2 could be applied to a particular case of myrmecophagous placentals, the aardvark. Tooth eruption and tooth number variation are well-reported for this species [START_REF] Lönnberg | On a new Orycteropus from Northern Congo and some remarks on the dentition of the Tubulidentata[END_REF][START_REF] Gros | A monograph of Orycteropus afer III, the skull, the skeleton of the trunk, and limbs[END_REF]Anthony, 1934b). An intraspecific study of the internal anatomy of adult aardvarks coupled with a developmental series could shed light on the homology of tooth loci in this toothless mammal. Additionally, this could help to understand the history of tooth loss in aardvarks, particularly to establish homologies between vestigial tooth loci and teeth present in fossil species (e.g., the "canine"; de [START_REF] De Bonis | The first aardvarks (Mammalia) from the late Miocene of Macedonia, Greece[END_REF][START_REF] Lehmann | The biodiversity of the Tubulidentata over Geological time[END_REF][START_REF] Lehmann | Amended taxonomy of the order Tubulidentata (Mammalia, Eutheria)[END_REF]. A second topic of interest comes from the discovery of a dentary pad, covered by orthokeratin, stretching along the putative tooth row locus in anteaters. This raises the question of the relationship between teeth and the evolution of keratinous structures on the mammalian jaws. An ongoing and very lively debate over the origin of keratinous structures (baleen) in mysticetes has drawn the attention of several recent studies [START_REF] Ekdale | Vascularization of the gray whale palate (Cetacea, Mysticeti, Eschrichtius robustus ): soft tissue evidence for an alveolar source of blood to baleen[END_REF]Peredo & Pyenson, 2017;Peredo et al., 2017[START_REF] Peredo | Tooth loss precedes the origin of baleen in whales[END_REF]Thewissen et al., 2017;[START_REF] Lanzetti | Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth-to-baleen transition[END_REF]. Sirenians are an interesting group in this regard, because all extant and recently extinct sirenians present a keratinized oral pad in the anterior part of the jaws, innervated by alveolar nerves [START_REF] Reep | Distribution and innervation of facial bristles and hairs in the Florida manatee (Trichechus manatus latirostris)[END_REF][START_REF] Marshall | Orofacial morphology and feeding behaviour of the dugong, Amazonian, West African and Antillean manatees (Mammalia: Sirenia): functional morphology of the muscular vibrissal complex[END_REF][START_REF] Csorba | A previously undescribed skull of Steller's sea cow, Hydrodamalis gigas (Mammalia: Sirenia: Dugongidae) in the Hungarian Natural History Museum[END_REF]. This clade presents a relatively wellknown fossil record (e.g., [START_REF] Domning | Libysiren sickenbergi , gen. et sp. nov.: a new sirenian (Mammalia, Protosirenidae) from the middle Eocene of Libya[END_REF] with species showing a complete dentition while others are completely toothless (i.e., Steller's sea cow). An ongoing project aims at µ-CT scanning most of the extant and fossil diversity of sirenian skull and mandibles, in order to understand the connection between teeth and the oral pad, through the use of dorsal canaliculi as an osteological proxy to vestigial tooth loci.

Additionally, this project aims to understand how tooth innervation evolved along with the horizontal tooth replacement pattern presented by manatees [START_REF] Domning | Horizontal tooth replacement in the Amazonian manatee (Trichechus inunguis)[END_REF][START_REF] Rodrigues | Continuous dental replacement in a hyper-chisel tooth digging rodent[END_REF].

Lastly, our study on the phenotypic covariance patterns in myrmecophagous mammals left one main axis of research open: the study of ontogenetic phenotypic trajectories. Tooth eruption is a main factor influencing covariation in the mammals skull (Mitteroecker & Bookstein, 2009). The use of developmental series of skulls is necessary to better understand the influence of tooth development in the functional repatterning of the mammalian skull. This could be achieved by collecting µ-CT scans of fetus from the most abundant myrmecophagous species (P. tricuspis and T. tetradactyla) in natural history collections. Comparing the ontogenetic phenotypic covariance trajectories of pangolins, anteaters, and two toothed sister taxa would reveal how precisely covariance patterns differ between toothless and toothed species, and between evolutionary replicates.

As a general conclusion, the approaches used in this thesis show that the combination of geometric morphometrics, µ-CT scanning, histology, and soft tissue staining provide the ability to dissect convergence through morphology. These techniques allowed to dive deeper into the complexity that underlies macroscopic adaptive evolution. Developmental constraints are ubiquitous across mammals, and any form of life (McGhee, 2001), and so is convergence (McGhee, 2011). By acting on developmentally integrated systems, selection drives change on morphological subunits in directions that are more likely to produce more adapted phenotypes (Riedl, 1978). This thesis allowed to understand that this theoretical assumption does not always translate into exactly identical morphologies in convergently evolved organisms. The phylogenetic context also constraints the intraspecific theoretical morphospace. The exposure to a certain environmental stimulus will therefore translate into the best compromise available [START_REF] Bock | Preadaptation and multiple evolutionary pathways[END_REF]. "Life finds a way", as a popular fictional chaotician once said, and I showed that multiple ways were found during the evolution of myrmecophagy. (USNM 033867, BMNH 11.10.27.3, LSUMZ 8538, LSUMZ 29160, ZMB 84-357, USNM 020920); (G-H) Cyclopes didactylus (MNHN 1986-1115, BMNH 24.12.4.68); (I-K) Tamandua tetradactyla (BMNH 34.9.2.196, MVZ 153482 The mandible of Cyclopes didactylus is low and slender. In lateral view, the horizontal ramus is thin, elongated and is highly curved with a ventral concavity, which makes it distinctive from all other anteaters. The ascending ramus is extremely inclined laterally, with the hook-like coronoid process projecting laterally. The mandible presents seven mental foramina (Figure S1A). We here designate the flattened part of the horizontal ramus of the mandible as the dentary pad. This dentary pad extends from the most anterior tip of the mandible to the posterior end of the coronoid process. This pad displays several dorsal foramina with foramina for dorsal canaliculi 9 to 15 forming a continuous groove. Nineteen foramina are present on the left dentary pad, 20 on the right mandible.

The mandibular canal displays a straight trajectory until it reaches the dentary pad, from where it curves ventrally, accompanying the shape of the mandible. The mandible has an elliptic-like section, and the major axis rotates, in anterior direction, from an almost transversal plane parallel position to a coronal one. The mandibular canal is positioned dorsally. The size of the mandibular canal remains constant along the horizontal plane, and decreases towards the symphysis. The mandibular canal presents several dorsal canaliculi (dc), which connect dorsomedially with the opening foramina. In total, there are fifteen dorsal (eighteen on the right mandible) and seven mental branches. Some of the dorsal canaliculi bifurcate and vary in diameter, with dc14 and dc15 being the largest (Figure S1A). The first four dorsal canaliculi (dc1 to dc4) are anterodorsally oriented, as well as dc12, dc13 and the anterior projections of the bifurcating canaliculi. The mental branches also vary in diameter, with the most anterior one (mb1) being, by far, the largest, but no specific trend observed.

Collared anteater (Tamandua tetradactyla)

In Tamandua tetradactyla the edentulous horizontal ramus is long, slightly curved ventrally, and gets gradually shallower postero-anteriorly. The dentary pad is more anterior, narrower in its most posterior part, and not as medially inclined as in C.

didactylus (Figure S1B); it is perforated by 17 foramina (Figure S1B, dc 1-15); a small and shallow groove connects the most posterior ones. Only one anterior mental foramen is present (Figure S1B,mb1). The ascending ramus is rather shallow and presents incipient coronoid and angular processes; the condyloid process is posteriorly projected.

The mandibular foramen (mb1, Figure S1B) is parallel to the mandibular canal.

The mandibular canal opens on the medial surface of the ascending ramus and projects

Giant anteater (Myrmecophaga tridactyla)

The mandible of the adult Myrmecophaga tridactyla is, in many ways, similar to that of T.

tetradactyla. It is larger in size but presents the same general morphology, with the body being elongated, transversely compressed and lacking teeth, and the ascending ramus being extremely simplified when compared to toothed xenarthrans. As in T. tetradactyla, the anterior part of the mandible is slightly curved, with the anterior tip tapering ventrally.

A dentary pad occupies more than half of the total length of the jaw (Figure S1C), which is narrow posteriorly. Sixteen foramina are present on the dentary pad, and correspond to the dorsal opening of the dorsal canaliculi. Two mental foramina are present in the anterior part of the mandible, with the most anterior one (mb1, Figure S1C) opening laterally at the level of dc4 and the second one (mb2, Figure S1C), much smaller, opening at the level of dc5.

The mandibular canal opens in the medial surface of the ascending ramus, just dorsally to the position of the coronoid process, with an aperture with a long anteroposterior axis. A groove runs anteriorly along the canal. The latter gradually descends along the lengthy horizontal ramus, until it reaches the level of the posterior margin of the dentary pad (Figure S1C). It then projects dorsally to reach the level of dc5, from where it maintains its position in the mandible until it opens to the mental foramen (mb1), anteriorly. Along this path, thirteen main dorsal canaliculi open dorsally in the dentary pad. Dc13, the longest and most posterior dorsal canaliculus projects postero-dorsally.

Dc12 to dc6 project dorsally, with some dorsal canaliculi displaying a simple column shaped, while others bifurcate dorsally. Dc5 is anteriorly inclined and has a much reduced diameter. Close to the symphysis, the first five dorsal canaliculi (dc1-5) form a distinct complex of long and anteriorly inclined canaliculi, similar to T. tetradactyla. In summary, the morphology of the mandibular canal of M. tridactyla is similar to T.

tetradactyla, except for the dorsoposteriorly oriented dorsal canaliculus (i.e. 13), and for the larger number of dorsal canaliculi on the anterior complex.

A juvenile specimen (ISEM -071 N) was also analysed to check on the number of dorsal canaliculi. There are 16 dorsal canaliculi on the left side and 18 dorsal canaliculi on the right hemi-mandible. The posterior part of the mandibular canal is not well ossified and the division between branches is less clear. The posteriormost dorsal canaliculus is long and posteriorly projecting and does not reach the top of the mandible.

Indian pangolin (Manis crassicaudata)

The mandible of Manis crassicaudata is greatly compressed transversely and shallow.

The ascending branch lack a true coronoid process as consists of a slightly dorsally inclined posterior knob-like projection. Three mental foramina (Figure S1D, mb1-3) are present on the anterior part of the horizontal ramus.

The mandibular foramen is antero-posteriorly elongated and has an anterior position in the ascending ramus. The mandibular canal projects anteriorly in a straight trajectory, near the dorsal margin of the mandible. From about the middle of the horizontal ramus the mandibular canal trajectory accompanies the dorsal edge mandible. This contrasts with anteaters, in which the mandibular canal position is ventral until it drifts dorsally at the posterior part of the dentary pad. The transversal section of the canal varies between a circular and an oval shape. From its most posterior part, the canal displays several small canaliculi that depart from the main mandibular canal, parallel to it. These parallel canaliculi are present around the mandibular canal, along its entire length, both dorsally and ventrally. Their density is higher on the anterior half of the horizontal ramus and the posterior part of the ascending ramus. On the anterior part of the mandible, the dorso-laterally projecting pseudo-tooth displays a small foramen for a parallel canaliculus and the very anterior tip of the horizontal ramus presents two of these canaliculi. Most parallel canaliculi show no connection to the mandibular canal and only a few open in microscopic foramina (Figure S1D). The most posterior mental branch (Mb3) is short and opens in an elongated foramen just before it bifurcates. The remaining two mental foramina (associated to mb2 and mb3) open laterally close to the sharp anterior tip of the mandible. The small mb2 splits posteriorly to the pseudo-tooth while the large and elongated mb1 drifts laterally at the level of this prong.

Malayan pangolin (Manis javanica)

The mandible in Manis javanica is shallower than in M. crassicaudata. It presents five anterior mental foramina (Figure S1E, mb1-5), with the second most anterior (mb2) being clearly larger than the remaining ones. Between the posterior end of the symphysis and the pseudo-tooth, two small circular foramina open medially (Figure S1E).

The mandibular foramen in M. javanica differs from M. crassicaudata; it displays an elliptical shape with an extremely elongated antero-posterior axis. The dorsal and ventral margins of the foramen fade posteriorly and its internal surface becomes continuous with the medial surface of the ascending ramus.

Similar to its sister taxon, M. javanica displays a mandibular canal that presents a rather homogeneous shape and position along its path. Posteriorly, it slightly descends accompanying the inclination of the mandibular foramen and follows the general shape of the dorsal margin of the horizontal ramus until it reaches the mental foramina. The transversal section of the mandibular canal becomes slightly dorso-ventrally compressed at mid-length, but immediately assumes its former shape anteriorly. As described for M. crassicaudata, several parallel canals are present along the entire length of the mandible. The density of these small canals is particularly high in the anterior portion of the mandible as well as in the posterior part, at the level of the mandibular foramen.

Their morphology is in all aspects similar to the structures observed in M. crassicaudata, including the presence of a couple of vertical canaliculi that project dorsally and open through two small foramina in the pseudo-tooth, as well as the presence of a couple of canaliculi that reach the mandible surface in all directions. The mandible presents five

Hairy long-nosed armadillo (Dasypus pilosus)

The anterior part of the slender mandible is sharp and its height slightly increases at mid-length of the horizontal ramus. A row of rather spaced peg-like teeth occupies the second third of the mandible. D. pilosus presents a c 1, p 7, m 1 lower dental formula.

The c1 and m1 present a basic peg-like shape. The anterior four mental foramina are positioned between the p 3 and the margin of the most anterior and largest mental foramen (Figure S1G, mb1), at the level of the fused symphysis. The most posterior and smallest of the five mental foramina is located posterior to the m 1 alveolus.

The symphysis is elongated, reaching the level of the anterior margin of mb1.

The mandibular canal is ventrally positioned at the level of the alveolar portion of the mandible. The canal opens posteriorly in a high mandibular foramen and extends ventrally towards the centre of the tooth row at the level of the fourth premolar. From this point it projects slightly dorsally, accompanying the shape of the mandible, until the level of mental foramen 3. Anterior to mb3, the mandibular canal presents a straight trajectory. Immediately dorsal to the mandibular canal, the horizontal ramus displays a small canal that originates in the p 6 alveolus and passes through all alveoli until p 2.

From this point it projects antero-dorsally, as a dorsal canaliculus, to reach the p 1 alveolus. From this alveolus it projects further antero-dorsally to the c 1 alveolus and extends in the same direction until the level of third mental foramen. This dorsal canaliculus presents a bifurcation anterior to c 1 (Figure S1G). A second dorsal canaliculus arises at the level of mental foramen 3, bifurcating and ending just anteriorly.

Neither of these canaliculi reaches the dorsal margin of the mandible. No foramina open in the anterior part of the mandible, close to the symphysis.

Giant armadillo (Priodontes maximus)

The mandible is long and displays a long tooth row extending for about half its total length. Similarly to D. novemcinctus and D. pilosus, the mandible is narrow, transversely compressed, although it is slightly more robust. As in anteaters, this mandible presents a medio-lateral rotation anteriorly. The left tooth row is composed of 22 hypselodont teeth, 23 on its right counterpart. In lateral view, three mental foramina (Figure S1H, mb 1-3) can be observed just anterior the tooth row. A fourth small one is present in the same area, but appears to be an extra branching of mental foramen (mb1) with no symmetrical branch on the right hemi-mandible.

The transversely compressed mandibular canal of P. maximus exhibits some differences compared to the other genus of armadillo here studied. The mandibular foramen is dorsoventrally elongated as in Dasypus but its position is more dorsal in the ramus when compared to the alveolar plane. The canal extends ventrally with a weak inclination (~12.2°). Posterior to mf 22, a large dorsal canaliculus (Figure S1H, dc3), slightly inclined posteriorly, projects dorsally and opens into several small foramina.

Anteriorly, although alveoli for mf 1 and mf 2 are almost adjacent to the canal, small dorsal canaliculi are visible. As the canal projects ventrally towards alveolus for mf16, the dorsal canaliculi become longer. Their morphology varies, being anteriorly oriented and sometimes bifurcated. These canaliculi vary in diameter and can bifurcate (e.g., below alveolus for mf 17 and mf 18, Figure S1H), with a branch projecting dorsally and the other anteriorly, to merge with the immediately anterior dorsal canaliculus. Anteriorly to alveolus of mf 16 the mandibular canal displays a parallel trajectory to the alveoli row until alveolus for mf 9. From this point, it projects dorsally until mental foramen 1, being positioned immediately ventral to the nine most anterior alveoli. Along its path to the symphyseal portion of the mandible, the mandibular canal displays several minor mental branches before it splits into three larger mental canals (Figure S1H, mb 1-3) anterior to the first alveolus. The most posterior and smaller mental branch splits from the main canal right anteriorly to alveolus for mf 1, projecting anterodorsally and then drifting laterally. A second larger mental branch (mb2) splits anteriorly, departing from the dorsolateral part of the mandibular canal and opening in an antero-posteriorly elongated foramen. The most anterior and largest mental branch (mb1) also opens into an antero-posteriorly elongated foramen. A more anterior small branch is visible on the lateral side of the mandible, but corresponds to a small ramification of the largest mental branch (mb1). Another canaliculus of the mandibular canal, which splits from the posterior part of the mb1, continues anteriorly toward the antero-dorsal end of the mandible. This small canaliculus (dc1) divides into three smaller ramifications, which open on the medial side of the anterior tip of the mandible.

Aardwolf (Proteles cristatus)

Proteles cristatus displays a mandible with a relatively high horizontal ramus displaying an anteriorly projected anterior margin. The specimen displays the following dental formula: i 3, c 1, p 2, m 2. This mandible displays three mental foramina (Figure S1I, mb1-3), with the first and second mental foramina displaying oval apertures of similar size. The first mental foramen is located on the anterior margin of the mandible and the second one is anterior to the canine, below the anterior end of the diastema. The third mental foramen is located below the diastema, half way through the height of the mandible.

The mandibular foramen is oval shaped, located in the middle of the ascending ramus, antero-ventral to the dorsal tip of the coronoid process. The mandibular canal has an oval section, being noticeably dorso-ventrally elongated from the anterior end of the coronoid process to the level of the m 1. The mandibular canal projects slightly ventrally until the posterior limit of the diastema. None of the four check teeth alveoli is adjacent to the mandibular canal. The first and second molars are dorsally placed relative to the canal; no dorsal canaliculus reaches their alveoli. The inferior alveolar nerve and artery branches reach the teeth through the many hollow cavities of the alveolar portion of the mandible. The trabecular nature of the molar area is particularly evident anteriorly (Figure S1I), dorsally and posteriorly to the premolar alveoli, almost reaching the dorsal edge of the mandible. Posteriorly, fused trabeculae form a sort of posteriorly projecting canals, which reach the dorsally placed m 1 and m 2 alveoli.

Anterior to the c, below the diastema, three mental branches (Figure S1I, mb1-3) split and project antero-dorsally. Mb3 projects dorsally and opens laterally right ventrally to the midpoint of the diastema. Mb2 projects antero-dorsally and is laterally inclined, opening latero-ventrally to the canine. Mb1 is long and projects antero-dorsally, passing through the middle of i 2 and i 3 and opens in the anterior margin of the mandible.

Dog (Canis lupus)

Canis lupus presents a mandible with a high ascending ramus, with a relatively broad coronoid process. The mandible presents 11 tooth loci (i 3, c 1, p 3, m 3) and contrasts with P. cristata in its complete tooth row (no diastema), its shorter symphysis and rather vertical anterior margin. Four mental foramina are present (Figure S1J, mb1-4). The first mental foramen opens anteriorly, ventral to i 2. The second and largest mental foramen opens laterally between p 1 and c 1. The third mental foramen opens at the level of the anterior root of p 3 and the fourth mental consists of a rather small lateral aperture located between the ventral tips of the anterior and posterior roots of p 4 and p 3, respectively.

The mandibular foramen resembles P. cristata, yet the canal projects slightly more ventrally. Just posteriorly to the anterior edge of the coronoid process, the mandibular canal becomes more extended anterodorsally (Figure S1J), displaying a pseudo elliptical cross section. This is a main characteristic of the mandibular canal of the dog. With the exception of m 3, teeth are rooted deeply enough to be in close contact with the dorsal edge of the mandibular canal. The trajectory of the mandibular canal follows the shape of the ventral margin of the mandible from the level of the posterior root of m 1 until p 2, where it branches (Figure S1J). The large m 1 is so deeply rooted that both its roots protrude ventrally into the mandibular canal. Along its trajectory, the mandibular canal is topped by a complex of trabeculae that surrounds the tooth roots. From about the second m 1 cusp, the mandibular canal gradually decreases in height anteriorly. All but the small fourth mental branch project anterolaterally. Mb4 is a very thin branch that projects posterolaterally below the posterior edge of p 3. Mb3 is comparatively larger and splits from the mandibular canal just ventrally the anterior root of p 3. Mb2 is large in diameter and projects anterolaterally ventrally to p 2 to open in an oval-shaped foramen between p1 and c (Figure S1J). Mb1 is a rather thin and extremely long ramification of the mandibular canal that projects anteriorly to pass dorsally to the c and i 1-3 roots and open in the anterior margin of the horizontal ramus. In its trajectory, mb1 opens to the alveolus of i 3. Dorsally to the branching point of mb1, a relatively large accessory branch of the mandibular canal projects anterodorsally. This branch is medially oriented and almost reaches the symphysis, posterior to which it divides into several trabeculae.

Pale-throated three-fingered sloth (Bradypus tridactylus)

In the adult Bradypus tridactylus, the mandible is characterized by a short but robust horizontal ramus, bearing one caniform (Cf) and three molariform teeth (mf 1-3), and a high ascending ramus. The tooth row almost occupies the entire length of the body of the mandible, with teeth inclination becoming more medial along the antero-posterior axis. All four teeth are tall, lack roots and are deeply rooted in the mandible. The mandible presents two mental foramina with one at the anterior tip of the mandible (Figure S1K, mb 1) and a larger one at the level of the mf 4 (Figure S1K, mb2).

The morphology of the mandibular canal is very distinct from that observed in anteaters and armadillos. The mandibular foramen is elliptical in shape, with the major axis oriented anteroposteriorly with a similar inclination to the condylar process. The canal projects antero-ventrally from the mandibular foramen until it reaches its lowest position in the mandible, at the level of the mf 3 At the same level, but higher in the body of the mandible, the largest and most posterior mental branch opens on the lateral side of the mandible, after branching midway between the mandibular foramen and the lowest mandibular canal position. The mandibular canal then runs anteriorly and gradually projects dorsally in the mandible until it reaches mental foramen 1. There is one small dorsal canaliculus (dc 1-3) for each of mf 1, mf 2 and mf 3. Dc4 is originates ventrally to mf3 but extends anterodorsally to reach the alveolus on its anterior margin.

The mandibular canal runs medial to the first tooth and divides into dorsal and mental branches. The mental branches follow the same direction and inclination as the main branch and eventually reach the anterior tip of the mandible, lateral to the symphysis.

The dorsal canaliculus assumes a steep trajectory (roughly parallel to the anterior margin of the mandible) and exits the mandible dorsally. This dorsal canaliculus likely corresponds to a remnant of the innervation/vascularization of an additional tooth locus identified in a previous work [S6] and opens anteriorly to alveolus for Cf. The juvenile specimen (ZMB 18834) displays a vestigial tooth in the same position; its mandibular canal of the foetus presents a similar general morphology, differing in number of mental and medial branches. The foetal mandible presents four foramina for accessory branches that open in the medial side of the mandible and four mental foramina. This mandible is much less ossified, compared to the adult.

Two fingered sloth (Choloepus hoffmanni)

The mandible of Choloepus hoffmanni presents shallower horizontal and ascending rami compared to B. tridactylus. The anterior tip of the horizontal ramus is shovel-shaped and elongated. The mandible bears three molariform teeth (mf 1-3) and one anterior caniniform tooth (cf). In total, the C. hoffmanni mandible presents four mental foramina, a large one at the level of the root of the coronoid process and three small ones anterior to the caniniform tooth.

Due to the differences in mandible shape, the morphology of the mandibular canal is also different between the two sloth genera. Here again, the dorsal canaliculi of the mandibular canal are present when the tooth alveoli are more dorsal. The canal starts at the level of the dorsal edge of the horizontal ramus and runs anteriorly until it reaches the level of the posterior margin of the tooth row. At this level, the mandibular canal bifurcates, with a mental branch (Figure S1L, mb4) projecting antero-laterally to open in a large mental foramen, just anteroventrally to the root of the coronoid process.

The main branch projects medially from the mandibular foramen, passing marginally ventrolaterally to mf 3. A small dorsal canaliculus of the mandibular canal (Figure S1L, dc 10) projects medially and allows for the innervation and vascularization of mf 3, which is medially oriented. As the mandibular canal runs anteriorly, its position gradually changes to a more medial one. This contrasts with the morphology of the mandible of the adult B. tridactylus, in which the mandibular canal is medially positioned along the entire length of the tooth row. Two dorsal canaliculi of the mandibular canal (df8-9) are ventral to the anterior half of mf2. Three dorsal canaliculi (dc5-7) reach the alveolus for mf 1. Dc5 is a small canal that splits at mid-lenght of the alveolus and joins the main canal just anteriorly to it (Figure S1L). From this canal, three small dorsal projections reach the alveolus. Two smaller additional innervation/vascularization canaliculi are present posteriorly (Figure S1L, dc 6-7). Close to the symphysis, the mandibular canal steadily projects dorsally. The main branch passes medially to the cf and, as in B.

tridactylus, its position is dorsal to the base of the alveolus. In fact, dorsal canaliculi reach the alveolus of the cf. The more posterior canaliculus (Figure S1L, dc4) bifurcates from the mandibular canal antero-ventrally just anterior to the alveolus for the cf.

Anteriorly, a small canaliculus (dc3) splits from the mandibular canal and projects laterally into the same alveolus. The third canaliculus that connects to the alveolus of the cf (dc1) is located just anterior to the mandibular canal steep antero-dorsal projection in the direction of the anterior tip of the mandible. A long dorsal canaliculus (Figure S3B, dc2) splits from the mandibular canal in the direction of the rudimentary alveolus of the vestigial tooth that is observed on earlier ontogenetic stages. The vestigial alveolus, located just antero-medially to the anterior edge of cf, is also innervated/vascularized, with the dorsal canaliculus further splitting in two ventrally to its dorsal opening. Three small mental branches (Figure S1L, mb1-3) are present in the anterior part of the mandible: the most posterior (mb3) departs from the mandibular canal to open laterally at the level of mb2; mb2 projects dorsolaterally near the dorsal margin of the mandible;

mb1 splits at about the same length as mb2, but projects anterolaterally. Anteriorly to the level of the foramen for mb1, a small branch (Figure S1L, ab) reaches the mandible shovel-shape projection and further divides into two small canals that open dorsomedially. These canals are not present in B. tridactylus.

The mandible of the foetus of Ch. didactylus (ZMB 4949) presents a lower level of ossification and allometric shape differences. Nevertheless, the mandibular canal of the foetus presents the same branch pattern as observed in the adult.

Aardvark (Orycteropus afer)

This mandible consists of a transversely compressed long and shallow horizontal ramus and a comparatively very high ascending ramus. The anterior half of the horizontal ramus is edentulous, while its posterior half presents three molars and two premolars (i 0, c 0, p 2, m 3; Figure S1M). trabeculae complex at the level of i 3 and i 2 alveoli. The anterior one also projects anterodorsally but it meets the trabeculae briefly anteriorly to its branching point. This trabeculae complex is located medially in the mandible and is associated with the i 2 alveolus and the symphysis.

Anatomical description of additional taxa

A total of 12 species were segmented in order to reconstruct the phylogenetic history of the absence/presence of dorsal canaliculi (Figure 1). One Afrosoricida (Tenrec eucaudatus) and one Macroscelidea (Rhynchocyon petersi) were additionally segmented to increase the number of species with relatively close phylogenetic affinities to Orycteropus afer (Figure 1). Neither of the 12 species described in this section presents dorsal canaliculi. With the exception of the brown rat (Rattus norvegicus) and the velvet free-tailed bat (Molossus molossus), all the species present mandibular canals very similar in shape (Figure S2A-I). The mandibular foramen displays a descending trajectory anteriorly until the third molar (m 3). It projects anteriorly, ventrally to the tooth row, with its dorsal margin that usually opens directly to adjacent post-canine tooth alveoli (Figure S2). In some species (e. In almost all species, an incisor branch projects anteriorly at the level of the most anterior mental branch, and usually splits into several trabeculae that wrap both canine and incisor teeth. In the rock hyrax (Procavia capensis), however, the incisor branch opens directly into the corresponding alveolus. The tailless tenrec (Tenrec ecaudatus, Figure S2F) also presents a slightly different morphology of the incisor branch, with the mandibular canal opening directly into the alveolus of the canine, with the latter being connected to the following alveolus. In the brown rat (Rattus norvegicus, Figure S2K) the incisor branch is absent, with the alveolus of the incisor tooth extending back into the ascending ramus of the mandible. The innervation/vascularization of the incisor tooth arrives ventral to the coronoid process, as the mandibular canal partially merges with the alveolus. Although the Malayan tapir exhibits a classical incisor branching of the mandibular canal, the latter differs in from other species by its extremely reduced diameter (Figure S2E). The overall shape of the mandibular canal of the brown rat is peculiar due to the extreme posterodorsal projection of the incisor alveolus (Figure S2K).

The mandibular canal merges with the incisor alveolus medially, just anteriorly to the mandibular foramen. It projects anteriorly at the level of the m 3 and its trajectory follows the shape of the dorsal margin of the incisor alveolus. The mandibular canal opens directly to the m 3 and m 2. In the most anterior portion of the alveolar part of the mandible, which corresponds to the alveolus of the m 1, the mandibular canal presents a relatively ventral position relative to the first molar alveolus, the tooth being likely innervated/vascularized via trabecular bone. The mandibular canal opens dorsolaterally in a single mental foramen, just anteriorly to the m 1. The velvet free-tailed bat also presents a distinct mandibular canal morphology (Figure S2L). Compared to other species, the mandibular canal is unusually high. Here again, all pre-canine tooth alveoli are adjacent to the mandibular canal. However, the mandibular canal seems to extend dorsally, in between tooth roots (Figure S2). This might be a result of the scan resolution compared to the reduced size of the specimen, for in other segmented placental mammals, those spaces are normally filled with trabeculae (Figure S2). Apart from this abnormal height, the mandibular canal of the velvet free-tailed bat resembles those of other toothed species; it is positioned ventrally to the tooth row and bifurcates anteriorly, with a mental branch that projects laterally while the other branch of the canal opens into a trabecular system wrapping the canine and the incisors. An anterodorsally projecting mental branch is also present and opens ventrally to the incisors, similar to the condition observed in carnivores (Figure S1I, J).

Homology of dorsal canaliculi between anteaters and baleen whales

The trigeminal nerve originates in the pons and has two different roots, a sensory and a motor root [S10]. The mandibular branch of the trigeminal is composed of both sensory and motor roots and is designated by inferior alveolar nerve (IAN) [S10]. The nerve enters the medial side of the mandible through the mandibular foramen, and is accompanied by the inferior alveolar artery [S11]. Typically, the inferior alveolar nerve separates into four types of branches [S10,S11]: the mylohyoid branch supplies the hyoid musculature; the dental/inferior dental branches supply molars and premolars, each nerve branch innervating one tooth; the incisor branch supplies canine and incisors. The mental branch supplies the lip integument (the number of mental branches may vary between taxa). Here, we will group dental and incisor branches to follow the nomenclature of previous references for edentulous placentals [S9].

In Tamandua tetradactyla, the large inferior alveolar nerve (Figure 4B

Intraspecific and bilateral variation of dorsal canaliculi

Dorsal canaliculi were present in all segmented anteater (n=8) and long-nosed armadillo (n=6) mandibles (Figure S4). All six long-nosed armadillos displayed an anterior dorsal canaliculi plexus splitting in three to six dorsal foramina (Figure S4A-F), including the juvenile (Figure S4F). A canine, as well as its corresponding dorsal canaliculus, was present in two specimens (Figure S4A, F). dorsal canaliculi, while the juvenile presented slightly more canaliculi with a slightly larger bilateral variation (16L/18R; Figure S4L-N). Nevertheless, the observed pattern of dorsal canaliculi morphology and distribution along the mandible is similar.

Insights into the ancestral number of teeth in anteaters

All known anteater fossil skulls are toothless [S12,S13]. However, our data confirmed that the earliest representatives of the group were toothed, assuming the homology between dorsal canaliculi and alveolar vestiges. There are, however, several limitations in using the number of dorsal canaliculi to estimate tooth number: 1) it is not clear weather bifurcating dorsal canaliculi would correspond to one or more alveoli-although bifurcating dorsal canaliculi mostly appear to correspond to only one tooth in P. maximus -which can lead to an overestimation of the number teeth with the present method; 2) a high mandibular canal merges the lower part of the dorsal canaliculi from the posterior part of the mandibular canal of the juvenile M. tridactyla makes it difficult to discriminate dorsal canaliculi; 3) intraspecific variation may partly explained the observed number of dorsal canaliculi, especially when comparing the bilateral variation to the interspecific variation observed in other clades within Xenarthra (Cingulata). If we were to reconstruct the dental formula based on the number of dorsal canaliculi regardless of the abovementioned arguments, we would propose that each mandibular quadrant of earliest Vermilinguans comprised between thirteen and seventeen teeth.

Ancestral state estimation of the tree internal nodes

Based on our dataset composed of extant species, we reconstructed the ancestral condition of placental mammals concerning the presence of dorsal canaliculi (figure al. [S14] to perform an ancestral state reconstruction under a continuous time Markov chain. The posterior probabilities for the presence of dorsal canaliculi are presented for as presented in Figure 1, obtained from www.timetree.org [S15]. This tree includes 29 species and 28 internal nodes. Due to the absence of fossil taxa in the analysis, all nodes presented posterior probabilities close to zero or one. The probability of the presence of dorsal canaliculi was high in all nodes within Xenarthra. Excluding this clade, the highest probability for the evolution of dorsal canaliculi was found in the most recent common ancestor (MRCA) of cetaceans (node 12), with 4.86%. We found a 0.37% probability for the evolution of dorsal canaliculi in the MRCA of all placentals (node 2). This suggests that the absence of dorsal canaliculi (0) likely corresponds to the ancestral condition of placentals. The ancestral state reconstruction was performed with the phytools package [S16] in R [S17].

6.2-Appendix 3

Supplemental information to Article 3 Enfin, j'ai disséqué les têtes de six spécimens de fourmiliers conservés à l'Institut de Sciences de p. ex., Cuvier, 1798). Edentata a été utilisé pour désigner ces taxons (Rose, 1892 ;Tims, 1908), sur la base de traits morphologiques communs considérés comme des synapomorphies du groupe.

La diagnose proposée par Huxley (1872) pour les Edentata (ou Bruta, qui se traduit par brut, grossier ou bête) reflétait certains des traits morphologiques convergents liés à la myrmécophagie. Il s'agit notamment de la perte ou de la réduction des dents, de la simplification de la structure dentaire, de l'hypsélodontie, de la monophyodontie (sauf chez certains tatous) et des membres antérieurs adaptés au fouissage [START_REF] Huxley | A manual of the anatomy of vertebrated animals[END_REF]. [START_REF] Huxley | A manual of the anatomy of vertebrated animals[END_REF] Ces propositions n'ont toutefois pas été corroborées par les analyses phylogénétiques moléculaires les plus récentes (voir ci-dessous).

Depuis les années 1980-1990, les phylogénies moléculaires ont fourni de plus en plus de preuves confirmant la polyphylie des Edentata [START_REF] Jong | Protein sequence analysis applied to xenarthran and pholidote phylogeny. The evolution and ecology of armadillos, sloths and vermilinguas[END_REF][START_REF] Springer | Endemic African mammals shake the phylogenetic tree[END_REF][START_REF] De Jong | Molecules remodel the mammalian tree[END_REF]Murphy et al., 2001b). Les pangolins sont désormais reconnus come le groupe frère des carnivores au sein des Laurasiatheria [START_REF] Sarich | Mammalian systematics: twenty-five years among their albumins and transferrins[END_REF]Murphy et al., 2001b ;a ;Meredith et al., 2011). Les oryctéropes forment un sous-clade (Afroinsectiphilia) avec les tenrecs, les taupes dorées et les rats à trompes, au sein du superordre des Afrotheria [START_REF] Waddell | Towards Resolving the Interordinal Relationships of Placental Mammals[END_REF][START_REF] Asher | The new framework for understanding placental mammal evolution[END_REF]Meredith et al., 2011). La position phylogénétiques des xénarthres au sein des placentaires restent mal définie [START_REF] Nishihara | Retroposon analysis and recent geological data suggest nearsimultaneous divergence of the three superorders of mammals[END_REF][START_REF] Teeling | Making the impossible possible: rooting the tree of placental mammals[END_REF][START_REF] Foley | Mammal madness: is the mammal tree of life not yet resolved?[END_REF], leur position changeant dans chacune des trois hypothèses proposées : i) Atlantogenata-Boreoeutheria (Fig. 1); ii) Afrotheria-Exafroplacentalia; iii) Xenarthra-Epitheria.

Jusqu'à présent, la racine de l'arbre placentaire n'est toujours pas résolue, et les trois hypothèses sont actuellement considérées comme équiprobables [START_REF] Nishihara | Retroposon analysis and recent geological data suggest nearsimultaneous divergence of the three superorders of mammals[END_REF][START_REF] Teeling | Making the impossible possible: rooting the tree of placental mammals[END_REF].

Néanmoins, tous fournissent des preuves non équivoques de la polyphylie des Edentata (sensu Cuvier), pointant du doigt le haut degré de convergence morphologique résultant d'une sélection directionnelle vers un régime alimentaire myrmécophage.

Objectifs de la thèse -Dans cette thèse, j'ai combiné des méthodes d'anatomie comparée et de morphométrie géométrique, en utilisant des techniques modernes de microtomographie assistée par ordinateur et des vastes collections muséales, afin de mieux comprendre l'évolution convergente de la tête, du crâne et des muscles des mammifères placentaires myrmécophages. Les études présentées ici se concentrent sur le crâne de 15 espèces myrmécophages, incluant les fourmiliers, le tatou géant, les pangolins, les oryctéropes et le protèle, ainsi que leurs groupes frères.

Dans le premier chapitre, j'ai utilisé une approche basée sur des points homologues pour décrire et quantifier les variations interspécifiques et intraspécifiques de la forme du crâne, ainsi que les modèles allométriques des pangolins (Pholidota), les mammifères les plus braconnés au monde.

Dans le deuxième chapitre, j'ai analysé l'anatomie interne de la mandibule de toutes les espèces placentaires myrmécophages et je l'ai comparée à des taxons non myrmécophages afin de ré-interpréter les patrons de convergence phénotypique et de discuter des aspects fonctionnels de la régression dentaire.

J'ai également utilisé des spécimens de collection et des données CTscans pour effectuer une description anatomique comparée des musculatures masticatoire, hyoïde, linguale et faciale des trois genres de fourmiliers (Vermilingua, Xenarthra).

Enfin, j'ai évalué et comparé les modèles de covariation phénotypique intra-et interspécifique chez les placentaires myrmécophages, en utilisant une approche de morphométrie géométrique. J'ai utilisé des méthodes exploratoires et confirmatoire pour comprendre l'impact de l'acquisition d'un mode de vie myrmécophage sur la modularité et l'intégration du crâne.

Principaux résultats -Dans le premier chapitre, j'ai que la forme du crâne peut permettre de différencier sept des huit espèces de pangolins actuelles. Mes résultats ont montré que les pangolins africains et asiatiques se distinguent par des trajectoires allométriques différentes au cours de l'ontogénie.

J'ai montré que la taille influence largement la forme du crâne ce qui représente un effet confondant pour déterminer des distances phénétiques entre groupes. J'ai également étudié la variation intraspécifique de la forme du crâne chez deux espèces à large répartition géographique, Phataginus tricuspis et Manis javanica. Bien qu'aucune discrimination n'ait été trouvée entre les différentes populations de M. javanica, j'ai montré qu'il existe un certain degré de différenciation morphologique entre les espèces cryptiques récemment proposées sur la base de données moléculaires.

Dans le deuxième chapitre, j'ai développé deux axes de recherche. Tout d'abord, j'ai décrit la morphologie mandibulaire interne des espèces actuelles de mammifères myrmécophages. En utilisant des méthodes de microtomographie à rayons X, j'ai montré que des structures supposément associées à l'innervation de la dent (canalicules dorsaux) sont présentes chez les fourmiliers, pourtant dépourvus de dents, alors qu'elles sont absentes chez les pangolins également édentés. L'anatomie comparative intra-et interspécifique permet de : i) montrer que les canalicules dorsaux sont invariablement présents chez les fourmiliers; ii) confirmer la relation entre les canalicules dorsaux et le développement dentaire précoce;

iii) montrer l'évolution indépendante des canalicules dorsaux chez les fourmiliers et les baleines à fanons.

De plus, j'ai pu montrer que, malgré la perte des dents, les canalicules dorsaux sont vascularisés et innervés.

Toujours dans mon deuxième chapitre, j'ai produit une description anatomique comparaée de la musculature de la tête des trois genres de fourmiliers actuels (Myrmecophaga, Tamandua et Cyclopes).

J'ai pu confirmer que les muscles adducteurs mandibulaires sont réduits chez les fourmiliers, tandis que les muscles intermandibulaires et de la langue sont bien développés. J'ai montré que l'appareil masticateur du fourmilier pygmée présente des proportions volumiques musculaires différentes de celles du tamanoir et des tamanduas. De plus, j'ai montré que la perte de l'os jugal chez le fourmilier pygmée est probablement liée à l'absence d'un muscle masséter profond et d'une partie du zygomaticomandibularis.

J'ai ensuite comparé les musculatures des fourmiliers à celles des pangolins et oryctéropes et montré que l'anatomie musculaire de leur appareil masticateur est très différente, malgré des régimes alimentaires similaires.

Dans le troisième chapitre, j'ai décrit la quantité et la répartition des corrélations entre différents traits ostéologiques sur le crâne de 15 espèces myrmécophages. J'ai montré que les modèles de modularité ressemblent globalement à ceux des mammifères placentaires non myrmécophages et que l'allongement du crâne a pu entraîner un léger remodelage des patrons de modularité dans la région du rostre. Mes résultats montrent un découplage apparent entre la fonction masticatrice et les patrons de modularité. J'ai notamment pu démontrer que les patrons de covariance changent significativement au cours de l'ontogenèse, au sein d'une même espèce. Des résultats préliminaires permettent également de discuter de l'effet de la superposition Procrustes sur des ensembles de données biologiques.

Discussion -Les résultats de mes recherches confirment que l'évolution adaptative vers la myrmécophagie a eu un impact majeur sur la forme du crâne. Les recherches incluses dans les chapitres 1 et 3 révèlent à quel point les axes de variation du crâne des mammifères placentaire sont conservés. Ils montrent que l'allométrie évolutive et ontogénétique sont des axes principaux de variation morphologique qui peuvent facilement répondre aux pressions de sélection [START_REF] Cardini | Larger mammals have longer faces because of size-related constraints on skull form[END_REF]Cardini, 2019). Dans le premier chapitre, nous avons montré que l'allométrie peut avoir un effet confondant dans certains axes de l'espace morphologique crânien des pangolins (Gaudin et al, 2009 ;Ferreira-Cardoso et al, 2019a). Si l'allométrie est génératrice de covariance phénotypique entre les caractères crâniens (Hallgrimsson et al., 2007 ;[START_REF] Porto | Size variation, growth strategies, and the evolution of modularity in the mammalian skull[END_REF], nous avons montré que les interactions fonctionnelles, comme celles entre muscle et os, n'ont pas un effet également évident sur les patrons de covariance. Nos résultats du chapitre 3 suggèrent que les modèles de modularité sont relativement inchangés chez les mammifères myrmécophages par rapport aux autres placentaires (Cheverud, 1982a ;Goswami, 2006 ;Parr et al, 2016 ;Heck et al, 2018). Ceci peut s'expliquer par des phénomènes de canalisation de la variation phénotypique du crâne [START_REF] Dworkin | Canalization, cryptic variation, and developmental buffering: a critical examination and analytical perspective[END_REF].

La sélection naturelle aura tendance à agir sur des ensembles de caractères fortement corrélés, maximisant ainsi l'évolvabilité des caractères (Riedl, 1978). Par conséquent, les changements morphologiques associés à la myrmécophagie sont probablement liés à la présence modules conservés au cours de l'évolution.

Si les patrons de variation phénotypique n'ont pas montré de changement commun associé à la myrmécophagie, les résultats des recherches présentés dans le chapitre 2 ont montré que certains de l'anatomie des espèces myrmécophages pourraient être très distincts malgré une ressemblance globale.

L'anatomie interne des mandibules des pangolins et des fourmiliers est différente, ce qui suggère les processus induisant une perte des dents sont distincts dans chacun de ces groupes. Ces différences anatomiques pourraient être en outre liées à des différences fonctionnelles, impliquant en particulier la biomécanique de leur appareil masticateur. La musculature masticatrice, intermandibulaire et de la langue des fourmiliers, des pangolins et des oryctéropes présente quelques similitudes mais aussi des différences significatives. Il en va de même au sein même des fourmiliers, le fourmilier pygmée présentant des proportions musculaires et un nombre de muscles masticateurs différents, qui pourraient expliquer des variations significatives de leur biomécanique masticatrice.

Conclusion

Pour conclure, les approches utilisées dans cette thèse montrent que l'utilisation combinée de la morphométrie géométrique, de la microtomographie à rayons X et de l'histologie m'a permis d'étudier dans le détail un exemple classique de convergence morphologique. Ces techniques ont permis de mieux appréhender la complexité qui sous-tend l'évolution du crâne des mammifères myrmécophages. Les contraintes de développement sont omniprésentes chez les mammifères (McGhee, 2001), tout comme les phénomènes de convergence (McGhee, 2011). En agissant sur des systèmes intégrés d'un point de vue développemental, la sélection conduit des sous-unités morphologiques à évoluer dans des directions qui sont plus susceptibles de produire des phénotypes « mieux » adaptés (Riedl, 1978). Cette thèse a permis de comprendre que cette hypothèse théorique ne se traduit pas toujours par l'acquisition de morphologies exactement identiques chez des organismes considérés comme convergents. L'exposition à certains stimuli environnementaux se traduira donc par le meilleur compromis disponible à un instant donné [START_REF] Bock | Preadaptation and multiple evolutionary pathways[END_REF].

"La vie trouve toujours un chemin", comme l'a dit un célèbre chaoticien de fiction, mais ce chemin peut être différent, en fonction des conditions de départ. J'ai montré que ce fut le cas avec l'exemple de l'évolution convergente des mammifères édentés.

7-Acknowledgements

First of all, I would like to thank Lionel and Fred for having trusted me with this thesis subject and for giving the to grow, professionally and personally, surrounded by mind-blowingly bizarre organisms (special mention to anteaters). I appreciate their willingness to let me explore the amazing world of cranial anatomy in whichever directions chance led me to (and it sometimes led me as far as North Korea). Lionel and Fred's patience and criticism during my PhD were priceless and I will be forever thankful to them for tempering and guiding my thoughts (and for playing 'Queen' during dissections; I give it up for Fred).

I want to leave a word of gratitude to my office mate during these three years, on whom I relied daily for all aspects of the PhD life. With him I shared most of my first thoughts, my joy, as well as my disappointments. Myself having a slight tendency towards pessimism, it took him a big deal of Buddhism (not the Rohingya massacre part) to be able to share the same work space with me. In a time in which technique is more valued than science, and in which curiosity tends to be replaced by business-like entrepreneurship, I was extremely lucky to have an office mate that was so excited about the complex simplicity of a skull, a tooth, or a vertebra. I will be thankful to him From the latter come people to whom I need to show my immense appreciation for all the moments we spent together during the last two years and who made the thesis redaction time more bearable. Therefore I thank to Quentin, for our wonderings in the maze of size correction, all those coffee breaks that overboosted our heart rates, and all those dance floor dominations. Rémi, thank you for all the encouraging words during my third year of PhD, for never telling Fred that I left the car in the middle the main road of Cayenne with the keys on it, and for all the gamelles that either saved me, but most often made me lose during our "meetings". I owe you a run to the Pic St. I would like to thank Denise and Alex for their kindness, but mainly for giving birth to Laura. She was part of the best moments for the last three years and was there for me during the worst. When I look back, I couldn't be happier (and feel luckier) that she accidentally had to come get her keys from her house mate after a busy day, which ultimately led us to meet. Thank you, Laura, for changing my life, for coming to visit me when I was working in collections abroad, for being so patient, and for making the good days immensely better and bringing a spark to the gloomy ones.

I want to dedicate this thesis to my patrons, the tax-payers of the European Union, especially those who always pay, never default, and rarely benefit: the proletariat.

Abstract

The subject of this thesis is the morphological convergence in the skull of ant-and termite-eating placentals. Its goals are to characterize tooth reduction, covariance patterns, and morphological variation of the skull, and explore their link to the selective pressures associated to myrmecophagy.

The first chapter focuses on the evolutionary, ontogenetic, and static variations of the skull in pangolins, a group of myrmecophagous animals that include the most threatened mammalian species on Earth. The morphological delimitation between seven of the eight species is demonstrated. Their ontogenetic allometric trajectories are described and the implications of the size variation on systematics are discussed. Additionally, intraspecific variation was partly associated to molecular distinctiveness of recently diverged cryptic species within the white-bellied pangolin. These results were obtained with the use of three-dimensional geometric morphometric methods.

The second chapter was dedicated to the comparative anatomy of the mandible and masticatory apparatus. First, I investigate the internal mandibular anatomy on a comparative sample of placental mammals using µ-CT tomography and histology. Structures putatively associated to tooth innervation (dorsal canaliculi) are present in toothless anteaters, while they are absent in pangolins, which are equally toothless. Comparative anatomy performed intra-and interspecifically allowed to: i) show that dorsal canaliculi are invariably present in anteaters; ii) confirm the relationship between dorsal canaliculi and early tooth development; iii) show the independent evolution of dorsal canaliculi in anteaters and toothless whales. Dorsal canaliculi are vascularized and innervated in the collared anteater, despite its tooth loss. This suggests that despite tooth loss, tooth pulp innervation likely maintained its sensorial role on the dorsal part of the mandible of anteaters. The second part of chapter 2 is devoted to the comparative anatomy of the head musculature of the three extant anteater genera. Classical and digital dissections confirmed the reduction of the masticatory apparatus in anteaters. The masticatory apparatus of the pygmy anteater is found to significantly differ from that the other two genera. A comparison with the head musculatures of pangolins and aardvarks was done, based on previously published studies. Despite being myrmecophagous, the head musculature of aardvarks and pangolins shows some key differences from that of anteaters. This suggests that the feeding apparatus of ant-and termite-eating placentals varies at the functional level.

The last chapter of this thesis covers the patterns of phenotypic covariance of the skull of 15 myrmecophagous species. A geometric morphometrics approach is used in order to explore and confirm hypotheses of modularity. Results show that patterns of modularity in myrmecophagous mammals resemble those of other placentals mammals. No common shift in the parcellation was found, other than that expected from the null hypothesis. Results suggest instead that skull elongation might have resulted on a slight remodeling of modularity patterns on the rostrum region in myrmecophagid anteaters. A preliminary analysis of ontogenetic trajectories of phenotypic covariance matrices in two myrmecophagous species shows that covariance patterns significantly change during ontogeny. This indicates that functional interpretations of static modularity and integration must be taken with caution.

Résumé

Cette thèse porte sur la convergence morphologique du crâne des mammifères placentaires myrmécophages, qui se nourrissent principalement de fourmis et de termites. Les objectifs ici sont de caractériser la réduction dentaire, les patrons de covariance et la variation morphologique du crâne, et d'explorer leur lien avec les pressions sélectives associées à la myrmécophagie.

Le premier chapitre se concentre sur les variations évolutives, ontogénétiques et statiques du crâne des pangolins, un groupe d'animaux myrmécophages qui comprend les espèces de mammifères les plus menacées sur Terre. La délimitation morphologique entre sept des huit espèces de pangolins est démontrée. Leurs trajectoires allométriques ontogénétiques sont décrites et l'influence des variations de taille sur la systématique du groupe sont discutées. De plus, la variation intraspécifique était en partie associée au caractère distinctif moléculaire d'espèces cryptiques récemment divergentes au sein du pangolin à petites écailles. Ces résultats ont été obtenus à l'aide de méthodes morphométriques géométriques tridimensionnelles.

Le deuxième chapitre était consacré à l'anatomie comparée de la mandibule et de l'appareil masticateur. Tout d'abord, l'anatomie interne de la mandibule a été étudiée sur un échantillon comparatif de mammifères placentaires par microtomographie et histologie. Les structures supposément associées à l'innervation des dents (canalicules dorsaux) sont présents chez les fourmiliers édentés, alors qu'elles sont absentes chez les pangolins également édentés. L'anatomie comparative intra-et interspécifique permet de : i) montrer que les canalicules dorsaux sont invariablement présents chez les fourmiliers ; ii) confirmer la relation entre les canalicules dorsaux et le développement dentaire précoce ; iii) montrer l'évolution indépendante des canalicules dorsaux chez les fourmiliers et les baleines à fanons. Les canalicules dorsaux sont vascularisés et innervés chez le fourmilier à collier, malgré la perte de ses dents. Ceci suggère, qu'en dépit de la perte des dents, l'innervation de la pulpe dentaire a probablement gardé un rôle sensoriel sur la partie dorsale de la mandibule des fourmiliers. La deuxième partie du chapitre 2 est consacrée à l'anatomie comparée de la musculature de la tête des trois genres de fourmiliers actuels. Les dissections classiques et numériques ont confirmé la réduction de l'appareil masticateur des fourmiliers. L'appareil masticateur du fourmilier pygmée est très différent de celui des deux autres genres. Une comparaison avec les musculatures crânienne des pangolins et des oryctéropes a été faite, uniquement basée sur des études publiées précédemment. Bien que myrmécophages, la musculature de la tête des oryctéropes et des pangolins présente quelques différences importantes avec celle des fourmiliers. Cela suggère que l'appareil masticateur des mammifères placentaires myrmécophages varie au niveau fonctionnel.

Le dernier chapitre de cette thèse couvre les modèles de covariance phénotypique du crâne de 15 espèces myrmécophages. Une approche de morphométrie géométrique est utilisée afin d'explorer et de confirmer les hypothèses de modularité. Les résultats montrent que les patrons de modularité chez les mammifères myrmécophages ressemblent à ceux des autres mammifères placentaires. Aucun changement commun dans la parcellisation du crâne n'a été détecté, autre que celui attendu de l'hypothèse nulle. Les résultats suggèrent plutôt que l'allongement du crâne a pu entraîner un léger remodelage des patrons de modularité dans la région du rostre des fourmiliers myrmécophagidés. Une analyse préliminaire des trajectoires ontogénétiques des matrices de covariance phénotypique chez deux espèces myrmécophages montre que les patrons de covariance changent significativement pendant l'ontogenèse. Cela indique que les interprétations fonctionnelles de la modularité statique et de l'intégration doivent être effectuées avec prudence.

Figure 1 -

 1 Figure 1 -Molecular-based phylogenetic relationships of extant mammals with emphasis in myrmecophagous placentals. Tree topology and branch lengths obtained from Timetree.org(Kumar et al., 2017). Divergence times (branch lengths) were adjusted for pangolins(Gaubert et al., 2018), xenarthrans(Gibb et al., 2016), and afrotherians(Meredith et al., 2011). Branches colored in red indicate myrmecophagous species; the branch colored in yellow indicates a non-obligate myrmecophagous species; tip labels in blue indicate clades previously historically ascribed to the Edentata.

Figure 2 -

 2 Figure 2 -Volume rendering of a µ-computed tomography scanned skull of Orycteropus afer, in lateral view. Points and numbers are examples of the types of landmarks used. Colors indicate left and right side bilateral landmarks.

Figure 3 -

 3 Figure 3 -Schemes of the three ways homoplasy arises (modified from McGhee, 2011). Left -convergent evolution of trait Z in species 3 and 6; middle -parallel evolution of trait Z in species 3 and 6; right -reverse evolution of trait R in species 6 within clade T.

Figure 4 -

 4 Figure 4 -Ecomorphology groups highlighted on the phenetic tree of extant mammals recovered by O'Leary et al. (2013; Fig S2), adapted from Springer et al. (2013). Green bar indicates the polyphyletic "Edentata".

Figure 1 .

 1 Figure 1. Evolution of Dorsal Canaliculi Linked to Tooth Regression in 28 Placentals and 1 Marsupial

Figure 2 .

 2 Figure 2. Evolution of Dorsal Canaliculi after Tooth Regression (A-F) (A) Cyclopes didactylus; (B) Tamandua tetradactyla; (C) Myrmecophaga tridactyla; (D) Manis javanica; (E) Orycteropus afer; (F) Priodontes maximus. Bone is transparent. Dorsal canaliculi, orange; mental branches, purple; mandibular canal, cyan; teeth, dark blue. Scale in mm. See also Figure S4 and Data S1.

Figure 3 .

 3 Figure 3. Ontogenetic Evidence of the Association of Dorsal Canaliculi to Vestigial Tooth Alveoli (A-D) 3D models of the mandibles of sloth fetuses (A) Bradypus tridactylus and (B) Choloepus didactylus) and adults (C) B. tridactylus and (D) Choloepus hoffmanni in medial (A, C and D) and lateral (B) views. Bone is transparent. B is a mirrored lateral view for a better perspective of the dorsal canaliculus. Dorsal canaliculi -orange; mental branches -purple; mandibular canal -cyan; teeth -dark blue. Zoomed details of the dorsal canaliculi associated with the vestigial teeth are shown. Scale in mm. See also Data S1.

Figure 4 .

 4 Figure 4. Histological Evidence for the Passage of Blood Vessels and Nerves in Dorsal Canaliculi (A) 3D-model of a mandible with a purple dashed rectangle indicating where the sagittal cut was performed; black dashed rectangles indicate the limits of the coronal cut. (B) Coronal cut showing the mandibular canal and a dorsal canaliculus; soft tissues are present dorsally to the mandibular canal, the dorsal canaliculus and the external dorsal, and dorso-lateral surfaces of the mandible; the red square represents the area of interest to be zoomed in (B'); the purple dashed line represents the sagittal section performed on the cut portion of the mandible (A). (C) Sagittal section showing the mandibular canal, two dorsal canaliculi and associated soft tissues; soft tissues on the dorsal surface of the mandible are identified; the red square delimits the area zoomed in (C'). (C') An ascending branch of the IAN is present in the dorsal canaliculus. Abbreviations: bo bone; de dermis; ep epidermis; IAA inferior alveolar artery; IAAab inferior alveolar artery ascending branch; IAN inferior alveolar nerve; IANa inferior alveolar nerve accessory branch; IANab inferior alveolar nerve ascending branch; IAV inferior alveolar vein; IAVab inferior alveolar vein ascending branch; pa keratinous dentary pad. See also Figure S3 and Data S1.

  Abbreviations

Figure 1 -

 1 Figure 1 -The skull (A) and mandible (B) of Tamandua tetradactyla. The skull is shown in lateral (up) and ventral (down) views. The area in green delimitates the temporal fossa. The mandible is shown in dorsal (up), medial (middle), and lateral (down) views. Anterior is to the left. Scale bar 10 mm.

Figure 2 -

 2 Figure 2 -The hyoid apparatus of Tamandua tetradactyla in lateral (A), ventral (B), and dorsal (C) views. Anterior to the left. Scale bar 10 mm.

Figure 3 -

 3 Figure 3 -The sternum of Tamandua tetradactyla in dorsal (A), lateral (B) views. Ccervical vertebrae; Tthoracic vertebrae. Anterior to the left. Scale bar 10 mm.

Figure 4 -

 4 Figure 4 -The masticatory and facial-masticatory musculature of Cyclopes didactylus in lateral (A, B), ventral (C), and dorsolateral (D) views. Scale bar 10 mm. The more superficial muscles were removed in B.

Figure 5 -

 5 Figure 5 -The pterygoideus and temporalis profunfus muscle complexes of C. didactylus (A), T. tetradactyla (B), and M. tridactyla in lateral (up) and dorsal (down). C is zoomed on the ascending ramus. Scale bar 10 mm.

Figure 6 -

 6 Figure 6 -The facial musculature of M. tridactyla (A, B), T. tetradactyla (C, D), and C. didactylus (E, F) in lateral view. A, C, and E show more superficial muscles; B, D, and F show deeper muscles. Scale bar 10 mm.

Figure 7 -

 7 Figure 7 -The intermandibular musculature, geniohyoideus, and pterygoideus medius of C. didactylus in lateral (A), ventral (B), and posteromedial (C) view. A small vestige of the interstylohyoideus is also depicted. Scale bar 10 mm.

Figure 8 -

 8 Figure 8 -The hyoid, thyroid, and pharyngial musculatures of C. didactylus in lateral (A, D), ventral (B, E), and posteromedial (C, F) view. Rectangle in E shows a zoomed posterior view of the thyroid-cricoid system. Scale bar 10 mm.

Figure 9 -

 9 Figure 9 -The sternum and pharyngeal musculatures, and the geniohyoideus of C. didactylus in lateral (A) and ventral (B) views. Scale bar 10 mm.

Figure 10 -

 10 Figure 10 -The masticatory and facial-masticatory musculature of T. tetradactyla in lateral (A, B), ventral (C), and dorsolateral (D) views. Scale bar 10 mm. The more superficial muscles were removed in B.

Figure 11 -

 11 Figure 11 -The intermandibular musculature, geniohyoideus, and interstylohyoideus, and sternomandibularis of T. tetradactyla in lateral (A), ventral (B), and posteromedial (C) view. Scale bar 10 mm.

Figure 12 -

 12 Figure 12 -The hyoid, thyroid, and pharyngial musculatures of T. tetradactyla in lateral (A, D), ventral (B, E), and posteromedial (C, F) view. Scale bar 10 mm.

  Fig 12A-C and 13) is a large muscle arising from the medioventral surface of the stylohyal. Its fibers are transversally oriented and arranged in a compact fashion laterally, conferring the Sph a sheet-like shape. Anteriorly, the Sph is in tight connection with the fibers of the mylohyoideus pars posterior (pp-Mh). Medially the muscle becomes thick as it inserts on the m-VP and the ventrolateral external surface of the nasopharynx. This description corresponds to the pars pharyngea of the Sph (sensuReiss, 1997). Posteriorly, the fibers have a longitudinal orientation, and form a fleshy projection that is pseudo-sigmoidal in cross-section (Fig.S2B). According toReiss (1997), this is the pars thyroidea of the Sph. As individual fibers were hard to delineate, the recognition of two parts in this muscle was not possible based on the contrast-enhanced scan. The posterior part of the Sph is flanked by the constrictures pharyngeus. Posteriorly, the Sph becomes mediolaterally thinner. It runs dorsolaterally along the wall of the oro-laryngopharyx. Part of the Sph posteriormost fibers present a small insertion on the posterior part of the dorsal surface. The remaining fibers attach to the medial wall of the inferior part of the constrictures pharyngeus (Fig. S2B).

Figure 13 -

 13 Figure 13 -The sternum and pharyngeal musculatures, mastostyloideus, and sternomastoideus of T. tetradactyla in lateral (A), dorsal (B), and ventral (C) views. Scale bar 10 mm.

  counterpart and becomes attached to the base of the tongue (genioglossus). Both Gh and pp-Mh wrap around the tongue, ventrally (both) and laterally (pp-Mh). Anteriorly, both right and left Sg are enveloped by a dermal tissue. At the level of the occipital condyles, the two Sgs become detached from the base of the tongue. The base of the tongue (genioglosssus) extends anteriorly, almost until the mandibular symphysis, attaching to the medioventral surface of the anterior third of both mandibles. The Sgs narrow anteriorly until the most anterior tip of the tongue.

Figure 14 -

 14 Figure 14 -The masticatory and facial-masticatory musculature of M tridactyla in lateral (A, B), ventral (C), and dorsolateral (D) views. Scale bar 10 mm. The more superficial muscles were removed in B.

Fig. 15 ;

 15 Fig.15; mylohyoideus pars media sensuNaples, 1999a) is only partially stained and thus not completely represented in our 3D reconstructions. This muscle forms a thick sheet ventral to the tongue musculature and the hyoid apparatus. Its fibers are transversely oriented, connecting a midline of conjunctive tissue to the medial surface of the mandible (Fig.15). Both symmetric counterparts of the pa-Mh unite in the midline, but could be easily distinguished both during the classical and digital dissections. The pa-Mh is clearly separated from the pars posterior by a shift in the insertion from the mandible to the skull. The posterior end and transition between the pars anterior and posterior of the mylohyoideus could not be segmented during the digital dissection.

Figure 15 -

 15 Figure 15 -The intermandibular musculature of M. tridactyla in lateral (A), ventral (B), and posteromedial (C) view. Scale bar 10 mm.

  First, we describe the presence of a tensor veli palatini (t-VP) in C. didactylus while this muscle is absent in T. tetradactyla. Secondly, the levator veli palatine (l-VP) presents a slightly individualized posterodorsal layer (Fig. S1) in T. tetradactyla while it forms a simple strap in C. didactylus. The medialis veli palatini (m-VP) is extremely elongated in T. tetradactyla compared to that of C. didactylus (Figs. 8 and 12). In the former, the posterior tip of the m-VP projects more posteriorly relative to the dorsal margin of the thyrohyal. Lastly, the ceratohyoideus (CeH) is relatively much larger in C. didactylus than in T. tetradactyla (Figs. 8 and 12). The only noteworthy difference is the attachment of the posterior part of the mylohyoideus pars anterior (pa-Mh) to the posterior part of the PM in C. didactylus. In T. tetradactyla and M. tridactyla, this muscle detaches from the mandible to attach directly to the pterygoid bone, posteriorly. 123 Facial musculature Differences in the facial musculature are related with the number of individual elements (Fig. 6). C. didactylus present the lowest number of muscles (n = 4) and M. tridactyla the largest number (n = 7), while T. tetradactyla is more intermediate (n = 5). The dilator nasi (DN) and the maxillolabialis profundus

Figure 5 -

 5 Figure 5 -Mechanisms responsible for generating trait covariation (adapted from Klingenberg, 2005).

Figure 7 -

 7 Figure 7 -Illustration of the skull of Myrmecophaga tridactyla (modified from Naples, 1999). Bones are colored according to the corresponding embryonic origin, neural crest (blue) and mesoderm (pink).

  digitization included specimens from the collections of the Natural History Museum (BMNH) in London (United Kingdom), the Museum für Naturkunde (MfN) in Berlin (Germany), the Muséum National d'Histoire Naturelle (MNHN) in Paris (France), the Institut des Sciences de l'Evolution in Montpellier (France), the Royal Museum for Central Africa (KMMA/RMAC) in Tervuren (Belgium), the American Museum of Natural History (AMNH) in New York (United States of America), the National Museum of Natural History (USNM) in Washington DC (United States of America), and the Museum of Vertebrate Zoology (MVZ) in Berkeley (United States of America). Our dataset is composed of cranial landmarks of 480 specimens from 15 extant species of myrmecophagous placentals and 21 specimens from non-myrmecophagous sister taxa. The myrmecophagous species include four anteater species (n = 215), seven pangolin species (n = 178), the aardvark (Orycteropus afer; n = 40), the aardwolf (Proteles cristatus, n = 25), the giant armadillo (Priodontes maximus; n = 14), and the bat-eared fox (Otocyon megalotis; n = 8).

Figure 3 -

 3 Figure 3 -Histogram of the within-and between-module correlations (ρ) for the main six modules of the placental skull (Cheverud, 1982; Goswami, 2006) for all 15 species. Blue bars represent raw correlations and pink bars represent allometry-corrected correlations (Tables2 and 3). Null values indicate either the absence of a module in the respective species or the inexistence of allometry in the sample.

  negative or low positive PC1 values, while anteaters (to the exception of Cyclopes didactylus), armadillos, and the aardvark score positive values. The sloths present low PC1 values, due to their short snout. PC2 explains 22.53% of the variance and explained the projection of the anterior margin of the maxilla, the posterior projection of the palatine, the position of the zygomatic processes of the maxilla and squamosal in respect to each other, and the length of the interparietal suture associated with a differential contribution of the supraoccipital to the skull roof (Fig.4). Toothless anteaters and pangolins show positive PC2 values while toothed species mostly present negative PC2 scores. Orycteropus afer and Tenrec ecaudatus also presented positive PC2 values closer to anteaters and pangolins. The toothless species with the lowest PC2 scores is Cyclopes didactylus (Fig 4).

Figure 4 -

 4 Figure 4 -Principal component morphospace of the interspecific dataset (n = 36). Morphospace formed by PC1 and 2 with points representing the average shape per species. (A) Points are colored by clade and scaled to centroid size; maximum and minimum shapes are presented for each axis with landmarks colored according to the seven-module architecture X identified for the interspecific dataset. (B) Phylogenetic relationships plotted on the morphospace; colors indicate diet and shapes indicate clades. Shape coordinates are allometrycorrected.

Figure 5 -

 5 Figure 5 -Morphological evolutionary rates (σ) of the face (A) and neurocranium (B) modules plotted on a phylogeny. Black color indicates slow evolutionary rates and red indicates fast evolutionary rates. σ values are log10-transformed.

Figure 6 -

 6 Figure 6 -Principal coordinates ordination of the covariance matrices of the 15 analysed myrmecophagous species. Each point represents a species. Points are coloured by Order: Vermilingua (orange), Cingulata (purple), Pholidota (dark yellow), Tubulidentata (brown), and Carnivora (Green).

Figure 7 -

 7 Figure 7 -Principal coordinates ordination of the covariance matrices of the interspecific dataset of P. tricuspis (A, B) and T. tetradactyla (C, D). Each point represents the covariance matrix of one of the four ontogenetic stages (juvenile to adult). The black arrows represent the ontogenetic trajectory of the covariance matrix for each species.

Figure S1 .

 S1 Figure S1. 3D models of fourteen mandibles (five toothless and nine toothed) in lateral view. Related to Figure 1. (A) Cyclopes didactylus (MNHN 1986-1115); (B) Tamandua tetradactyla (BMNH 34.9.2.196); (C) Myrmecophaga tridactyla (ISEM -065 V); (D) Manis crassicaudata (BMNH_67.4.12.298); (E) Manis javanica (BMNH 9.1.5.858); (F) Dasypus novemcinctus (USNM 033867); (G) Dasypus pilosus (ZMB 19240); (H) Priodontes maximus (ZMB 47528); (I) Proteles cristatus (BMNH 34.11.1.5); (J) Canis lupus (LAMC 23010); (K) Bradypus tridactylus (MNHN 1999-1065); (L) Choloepus hoffmanni (Hautier pers. Coll.); (M) Orycteropus afer (BMNH 27.2.11.113); (N) Potamogale velox (ZMB 71587). Bone is transparent. Dorsal canaliculi (numbered) -orange; mental branches (mb) -purple; mandibular canalcyan; parallel canaliculiyellow. Scale in mm.

Figure

  Figure S2. 3D models of 12 toothed mandibles in lateral view. Related to Figure 1. (A) Dasyurus hallucatus (TMM M-6921); (B) Lemur catta (DPC-O92); (C) Cynocephalus volans (FMNH 56521); (D) Procavia capensis (UMZC H4980K); (E) Tapirus indicus (KUPRI 506); (F) Tenrec ecaudatus (Martinez pers. coll.); (G) Lepus europaeus (DMET-RN1); (H) Talpa europaea (Martinez pers. coll.); (I) Tupaia montana (FMNH 108831); (J) Rhynchocyon petersi (BMNH 55149); (K) Rattus norvegicus (HACB-RN1); (L) Molossus molossus (AMNH 234923). Bone is transparent. Mental branches (mb) -purple; mandibular canalcyan; teethdark blue; trabeculaegreen. Scale in mm.

Figure S3 .

 S3 Figure S3. Histological slice of coronal sections of the mandibles of a bowhead whale and a collared anteater. Related to Figure 4. Coronal sections of the mandibles of (A) Balaena mysticetus [S1] and (B) a formalin preserved Tamandua tetradactyla (ISEM 778N; LFB stained). For B bone tissue is colored in dark blue and soft tissues stained in different tones of blue and purple. The dark blue colored myelin layers can be observed. Coronal cuts showing the mandibular canal and dorsal canaliculi; soft tissues are present on mandibular canals and dorsal canaliculi. bo bone; IAA inferior alveolar artery; IAAa inferior alveolar artery accessory branch; IAAab inferior alveolar artery ascending branch; IAN inferior alveolar nerve; IANa inferior alveolar nerve accessory branch; IANab inferior alveolar nerve ascending branch; IAV inferior alveolar vein; IAVab inferior alveolar vein ascending branch; vt vestigial tooth (1st generation).

Figure S4 .

 S4 Figure S4. 3D models showing intraspecific variation of dorsal canaliculi. Related to Figures 1 and 2. (A-F) Dasypus novemcinctus(USNM 033867, BMNH 11.10.27.3, LSUMZ

  anteriorly with a slight ventral inclination. It projects dorsally from the posterior edge of the dentary pad, as is typical of toothed mammals after tooth loss[S2,S3]. Similarly to C. didactylus, dorsal canaliculi are present. Each quadrant presents 15 dorsal canaliculi; only dc1 and dc15 are bifurcated (FigureS1B). The canals of the dorsal canaliculi are relatively narrower than those observed in C. didactylus. Although the most anterior canals (dc1 to dc6) are slightly anteriorly oriented, this trend is not present on the most posterior ones (dc7 to dc14), which display a more random inclination. The most posterior canaliculus (dc15) is posteriorly inclined. Dorsal canaliculi dc1 and dc2 are spatially and morphologically distinct from the remaining (FigureS1B), and highly anteriorly inclined. Dc1 is extremely elongated and splits into two parts anteriorly.

  mental branches: the three more posterior ones(Figure S1E, are short and small, and open laterally in small elliptical foramina posterior to the pseudo-tooth; the largest mental branch (FigureS1E, mb2) drifts antero-laterally to form a short branch at the level of the prong, opening in a large diamond shaped foramen; the most anterior mental branch (FigureS1E, mb1) represents the last remaining part of the main mandibular canal that projects anteriorly and opens just ahead of mb2 in an low and antero-posteriorly elongated foramen anterior to the pseudo-tooth.Nine-banded armadillo (Dasypus novemcinctus)Dasypus novemcinctus displays a thin, low and elongated horizontal ramus and a slightly broader ascending ramus characterized by its high and slender coronoid process. Anteriorly, the mandible is extremely low and transversely compressed, and displays a short symphysis. It is higher posteriorly and becomes transversely wider at the level of the tooth row. The dental formula is c 1, p 7, m 1. The anterior quarter of the mandible is completely toothless but an alveolus for a canine [S4,S5] is visible at the level of the first mandibular foramen (FigureS1F, mb1), and is separated from the rest of the tooth row by a small diastema. The molar is not erupted. This specimen displays two mental foramina: the most posterior one (mb2) is located between the second and the third premolars while the anterior one (mb1) opens anteriorly to p 1.Below the anterior edge of the coronoid process, a slightly elongated mandibular foramen opens on the medial surface of the ascending ramus, at roughly the same height of the alveoli. It projects ventrally with an inclination of around 14° until the posterior end of the tooth row. The canal describes a shallow dorsal facing concavity contouring the alveoli ventrally and accompanying the curvature of the ventral edge of the horizontal ramus. Immediately anteriorly to the third premolar, a slightly anterodorsally inclined posterior mental foramen is present on the medial side of the mandible.Anteriorly to the first molar, the main branch of the mandibular canal opens laterally in an antero-posteriorly elongated mental foramen. This foramen is particularly large and elongated. Anteriorly to the first molar, a dorsal canaliculus with a rather large diameter is also oriented antero-dorsally in the direction of the alveolus for the canine. The canaliculus opens in the alveolus and continues anteriorlywith less than half the diameterto split into two ramifications. The most posterior ramification bifurcates just dorsally to mental foramen 1 and opens into two small foramina (FigureS1F, dc 1c,d) on the dorsal margin of the mandible. The anterior ramification (dc 1a,b) describes a long trajectory antero-ventrally to dc 1c,d, and bifurcates near the anterior tip of the mandible. All bifurcation of the dorsal canaliculus (dc 1a,b,c,d) open into tiny foramina on the dorsal side of the mandible. In a juvenile specimen (USNM 020920), the canal does not open directly into the first five premolars and the canine. Therefore, the juvenile mandible displays longer dorsal canaliculi for the premolar dentition than the adults. A large dorsal canaliculus is associated to the first molar, which is absent. Anterior to the canine, a dorsal canaliculus projects anterodorsally, splitting in a plexus of three smaller canaliculi that open dorsally in three individual foramina. The dorsal canaliculi pattern is similar to the one observed in adults.

  The molars are large and deeply rooted and display an oblanceolate shape in dorsal view; the premolars are much smaller, transversely compressed, and are rooted more dorsally. The mandible of Orycteropus afer displays four major mental foramina(Figure S1M,, with six small mental branches laterally positioned compared to the tooth row(Figure S1M,. A total of seven foramina for dorsal canaliculi are present. The anteriormost four foramina are aligned just anteriorly to p 5 (sensu [S7]; dc3). Another small foramen is present anteriorly, at the level of the third mental foramen (dc2). Two slightly larger and longer foramina open between mental foramina 1 and 2 (dc2). The most anterior foramen (dc 1) opens anteriorly in the middle of the anterior apical portion of the mandible. The dc1 foramen resembles the reticular alveolar foramen of whales [S8,S9].The mandibular foramen is narrow and located well above the tooth row level, from where the canal projects ventrally. Between m 3 and m 1, the trajectory of the mandibular canal changes as it gradually projects dorsally, accompanying the height decrease of the horizontal ramus. The mandibular canal is adjacent to alveoli of m 1-3 and dorsal canaliculi are absent. From m 3 to p 5, only mental branches bifurcate from the mandibular canal (mb 5-10). The p5 and p6 alveoli are placed more dorsally in the mandible and are connected to the mandibular canal by two dorsal canaliculi, which project antero-dorsally. The two canaliculi dorsal to p 5 and p 6 (dc3 and dc4) are connected by a small canal parallel to the mandibular canal. Anterior to p 5, the main dorsal canaliculus (dc3) steadily extends dorsally, and then divides into four small canals linked to foramina dorsally. At the level of mb4, dc3 projects ventrally to merge with the mandibular canal, and a new dorsal canaliculus (dc2, FigureS1M) projects anterodorsally. Dc 2 is long and presents a small diameter. It bifurcates three times: just anteriorly to its origin, a small ramification projects antero-dorsally to open at the level of mb4; the dorsal canaliculus continues anteriorly and bifurcates again between mb1 and mb2, with one branch projecting antero-dorsally but never opening dorsally; a thin branch of dc2 continues until it splits in several smaller canals near the third mental foramen, with one of them opening dorsally at the level of the second mental foramen.Mb2 and dc1 split near the anterior end of the mandibular canal. Dc1 bifurcateswith one branch projecting antero-dorsally and the other anteriorlybefore it opens in two foramina. The most posterior branch of dc1 opens at the level of the second mental foramen. The most anterior canaliculus reaches the anterior tip of the mandible, ending in a foramen similar in position to the reticular alveolar foramen found in rorquals [S8,S9].Giant otter-shrew (Potamogale velox)The mandible of Potamogale velox presents a relatively low horizontal ramus with a rather long and anteriorly inclined symphysis. The ascending ramus of is high due to the presence of a broad sub-triangular coronoid process. The tooth row is composed of ten teeth (i 3, c 1, p 3, m 3). Three mental foramina are present in the mandible (FigureS1N, mb1-3). The first mental foramen is small and opens on the anterior margin of the mandible. The second and third mental foramina are relatively larger and open laterally at the level of p1 and the posterior root of m1, respectively.The mandibular foramen has a pseudo circular shape. Posteriorly, the mandibular canal presents a slightly descending trajectory until it reaches the m 2. The trajectory is then practically horizontal until the canine. Small complexes of trabeculae are present dorsally to the mandibular canal. The trabeculae surround the tooth roots, which are deeply implanted in the mandible. With the exception of the c and i 1-3, all alveoli enter in contact of the mandibular canal. The most posterior mental branch(Figure S1N, mb3) is the largest in diameter and projects laterally at the level of the tip of m 1 posterior root and opens slight dorsally in an elliptical shaped foramen. At the level of p 2, the trajectory of the canal drifts slightly dorsally, accompanying the small ventral concavity of the ventral edge of the horizontal ramus. Two branches split from the mandibular canal, dorsal to p 1, and project laterally. These branches merge into one larger mental branch, opening laterally in a single foramen(Figure S1N, mb2). Mb1 consists of a rather long branch, small in diameter, which projects anteriorly(Fig S1N, mb1). This branch passes ventrally to c alveolus and gradually projects dorsally to open anteriorly, between i 2 and i 1. Two accessory branches of the mandibular canal split at the level of p 1 and c. The posterior one projects anterodorsally until it divides into a

  FigureS2E) constitutes the most remarkable case of innervation/vascularization via trabeculae, with a mandible characterized by non-adjacent tooth alveoli and mandibular

  ', IAN) is placed dorsally in the mandibular canal. Two accessory branches of the IAN (Figure 4B', IANa) are present dorsolaterally to the IAN. The inferior alveolar artery (Figure 4B', IAA) lies dorsally to the IAN. An irregularly shaped branch of the inferior alveolar vein (Figure 4B', IAV) is placed laterally to the IAA. A third branch of the IAN (Figure 4B' and S3B, IANa) is visible dorsally to the IAA. Dorsally to it, the ascending branch of the IAV (Figure 3B' and S3B, IAVab) is present in the dorsal canaliculus of the mandibular canal. A keratinous dental pad covers the dorsal part of the mandible (Figure 4C, pa). Ventrally, the epidermis consists of a small layer (Figure 4C, ep) and, which lies dorsally to the thick dermis layer (Figure 4C, de). In addition to connective tissue, the dermis presents several blood vessels and small nerve branches. The most posterior dorsal canaliculus allows for the passage of an ascending branch of the IAN (Figure 4C,C', IANab1); the anterior dorsal canaliculus displays a large ascending branch of the IAA (Figure 4C, IAAab) and likely features a second ascending branch of the IAN (Figure 4C, IANab2) that projects anterodorsally.A histological section (coronal plane) of the mandible of a bowhead whale (Balaena mysticetus) showing the 15 th vestigial tooth [S1] shows the mandibular canal and associated soft tissues (inferior alveolar nerve, blood vessels) with two small canals (FigureS3A, red squares) dorsally. The most dorsal small canal is most likely associated to the vestigial teeth observed in the figure, while the most ventral one is associated to the 14 th vestigial tooth. Its position between the mandibular canal and the tooth row, plus the presence of branches of the inferior alveolar artery and the inferior alveolar nerve inside these small canals, highly suggest that these are homologous to the dorsal canaliculi observed in the collared anteater (T. tetradactyla). Dorsal canaliculi are anteriorly inclined in whales [S9], thus histological slices produce circular section for each canaliculus.

Figure S1 -

 S1 Figure S1 -Coronal sections of the µCT scans of Cyclopes didactylus (A, B) and Tamandua tetradactyla (C-F). A -the arrow shows the separation between the pars anterior (pa-MS) and the pars posterior (pp-MS) of the masseter superficialis; B -bipennate architecture of the temporalis superficialis and axis of pennation indicated by the arrow; C -the arrow points to the midline raphe of the pars anterior of the mylohyoideus (pa-Mh); D -the dashed yellow line shows the division between the pars anterior (pa-PM) and the pars posterior (pp-PM) of the pterygoideus medius; E -absence of a midline (arrow) raphe on the intermandibularis anterior (IA); F -passage of the sublingual artery splitting the pars anterior (pa-Mh) and the pars posterior (pp-Mh) of the mylohyoideus.

Figure S2 -

 S2 Figure S2 -Coronal sections of the µCT scans of T. tetradactyla. A -the arrow shows the separation between the anterior ("tensor") and the posterior ("levator") parts of the levator veli palatini (l-VP); B -the arrow indicates the separation between the constrictores pharyngeus muscle complex (CP) and the stylopharyngeus (Sph).

  l'Evolution (Montpellier, France) et à l'Institut Pasteur de Guyane (Cayenne, France). Ces spécimens ont été disséqués à Montpellier et à Cayenne, puis colorés à l'iode afin d'augmenter le contraste des muscles de la tête et de permettre une reconstruction numérique de leur morphologie. Des coupes histologiques ont été également réalisées sur plusieurs de ces spécimens (muscles et mandibules) à l'Institut de Recherche en Cancérologie de Montpellier (IRCM).Analyse des données -Toutes les données morphométriques ont été traitées et analysées à l'aide du logiciel gratuit d'analyse statistique R(Team, 2013). Des procédures d'analyse de morphométrie géométrique ont été mises en oeuvre avec le package geomorph v.3.5.0.0 R(Adams et al., 2017) et le code R fourni dans Claude (2008).. Les packages et fonctions R utilisés sont listés dans chacun des chapitres. Cadre phylogénétique -En 1742, le médecin et naturaliste français Félix Vicq-d'Azyr publie le deuxième volume de son "Système anatomique : quadrupèdes" (Vicq-d'Azyr, 1742), dans le cadre d'une collection intitulée "Encyclopédie Méthodologique". Dans ce livre, Vicq-d'Azyr nomme un nouveau clade de mammifères qu'il désigne sous le nom d'"édentés/Edentati", le trait diagnostique pour ce groupe étant l'absence d'incisives. Il comprenait quatre groupes, dont les paresseux (Pigri), les tatous (Loricati), les fourmiliers et l'oryctérope (Myrmecophagi), et les pangolins (Squammei) (Vicq-d'Azyr, 1742). Le nom Edentata a été adopté postérieurement par les naturalistes et sa structure a été réorganisée en cinq groupes différents : tatous, fourmiliers, paresseux, oryctéropes et pangolins (

  divise les Edentata en deux groupes en fonction de leur alimentation : à base de plantes (paresseux ; Phytophaga) ou d'insectes (Entomophaga). Ce dernier groupe comprend les fourmiliers, les pangolins, les tatous et les oryctéropes. Chacun de ces taxons a été placé séparément dans son propre taxon, pour qui aucune affinité provisoire n'a été proposée. Au moment où Huxley publie ses travaux, un peu plus d'un siècle après la formalisation du groupe des Edentata, une somme croissante de connaissances sur l'anatomie et la physiologie de ces mammifères permet désormais aux chercheurs d'interroger la pertinence d'un tel regroupement. Huxley (1872) lui-même précède sa diagnose et sa description des Edentata en déclarant que le groupe était "mal défini" et hétérogène.Cependant, il faudra attendre le début des années 1900 pour voir apparaître la première division officielle en trois ordres clairement différents.Weber (1904, p. 412) soutient que, bien qu'il soit devenu habituel de regrouper ces taxons dans le même ordre, les différences morphologiques sont trop nombreuses pour qu'une telle classification soit cohérente. Simultanément, Weber fait référence à la réduction de la dentition et à la simplification de la structure dentaire comme à une "réduction et transformation multiples" (traduit de l'allemand) qui ne pouvait être utilisée comme facteur de regroupement (voir ci-dessous).[START_REF] Weber | Die Säugetiere. Einführung in die Anatomie und Systematik der recenten und fossilen Mammalia[END_REF] considérait les Edentata comme un groupe "inférieur" au sein des mammifères thériens, les Paratheria, ne décrivant pas pour autant ses relations avec les autres mammifères.[START_REF] Weber | Die Säugetiere. Einführung in die Anatomie und Systematik der recenten und fossilen Mammalia[END_REF] a divisé les Edentata en deux groupes : i) les Nomarthra comprenant deux ordres d'espèces à articulation vertébrale normale (pangolins et oryctéropes); ii) les Xenarthra possédant des articulations accessoires anormales dans les dernières vertèbres thoraciques et lombaires (fourmiliers, paresseux et tatous). De plus, Weber (1904) a inventé le terme Pholidota, l'ordre dans lequel les pangolins sont toujours classés, remplaçant ainsi la désignation Squamata qui était synonyme de clade de reptiles. Au sein de Xenarthra, il a maintenu les divisions précédemment utilisées entre les fourmiliers (Myrmecophagidae), les paresseux (Bradypodidae) et les tatous (Dasypodidae). Depuis le début du XXe siècle, le nom Edentata a été utilisé pour désigner les Xenarthra, les similitudes entre ces derniers et les Pholidota et Tubulidentata ayant été attribuées à une évolution convergente vers la myrmécophagie (par exemple, Rose & Emry, 1993 ; McGhee, 2011). Cette classification a été largement acceptée, avant même l'avènement des méthodes de phylogénie moléculaire, les Xenarthra étant considérés comme un clade séparé au sein des Eutheria, divisé en deux ordres : les Cingulata (armadillos) et les Pilosa (paresseux et fourmiliers) (McKenna, 1975). McKenna (1975) a considéré les Pholidota comme un clade incertae sedis, tandis que les Tubulidentata ont été regroupés avec les ongulés avec un rang similaire aux ordres des artiodactyles, proboscidiens ou siréniens.

  ad vitam aeternam for showing me the beauty of comparative anatomy and of the anatomist profession, and for being a perfect model of how a top researcher should think and work. Lastly, I apologize to him for keeping all those skins in the office. Thank you, Lionel.All ISEMers, especially the ground floor teams (molecular phylogeneticists and paleontologists), are to be thanked. I owe Pierre-Henri, for his warm welcome from day one, his never-ending jokes, and his enthusiasm for natural history. Cheers, PH. Special thanks to Mélanie, who was my first PhD supervisor (!), and shared the office with me for around one year, and the dissection room for another iodine-stinking year. I want to thank Renaud, for all his help with the µCT scan and 3D modelling, to Julien and Allowen for their help with morphometrics and modularity. Special thanks to Hélder for all discussions and encouragement during the last days of his post-doc life at Montpellier. I also want to thank Ricardo, my master's mentor in Portugal and colleague at the lab for two years. Lastly, but most importantly, I want to thank to all PhD students and post-docs from the lab, mainly those in Phyl Evol Mol.I have to give a special mention to my collaborators, colleagues, and museum curators who made my work possible. Guillaume, Vielen Dank für all Ihre Hilfe, Ihren Rat und Ihre Thanks to Philippe, for his help with pangos, to Benoit for all the help in French Guiana, and to Anthony for bringing the anteater heads to this side of the pond. To Kévin, I thank very much for our friendly discussions, for the debates about modularity, and for the priceless favor you did to me by bringing me specimens from Paris. I immensely appreciate all the help provided by the collection curators of the AMNH (New York), USNM (Washington; thanks Louise Emmons), MfN (Berlin), MNHN (Paris), KMMA/Africa Museum (Tervuren), JAGUARS, and Institut Pasteur (French Guiana). Special thanks to Roberto and to the NHM collections (London) for the warm receptions and valuable help in London.Fortunately, a good part of the three-year period of the PhD was filled with non-working hours. Part of that time was spent with friends from ISEM. Being a foreigner, getting to know everyone's names took a few more days than expected… So thanks Paul, for having an easy name to memorize, for showing me OSS 117, and for accepting the death of your computer that I inadvertently anticipated. Thank you Manon, Marjo, Clémentine des Vosges, Yoann (le petit), Yoann (le grand), Corentin for warmly welcoming this migrant. After proving that I pay taxes and explaining that I am into anatomy (and therefore will be no threat in the race for a permanent position, other than at McDonald's), you have all welcome me to Montpellier and filled a very special place in my life. I also thank to all the friends from the French classes, Heliana, Clarissa, Charlotte, Oscar, and especially Valerio, with whom I co-celebrated the end of the PhD, and who I almost killed during our bike ride to the Pic St. Loup. Of the many people with whom I had the privilege to spend time with, while at Montpellier, I would like to make a special mention to Andrea, Pauline, Marina, Clémentine de Bretagne, Louise-Anne, Blaise, Emeric, Jihad, and Kévin.Many thanks to Laure, Elodie, Camille, Julien, Brice, and Nicolas (and Mathys, whose neocortex recently started to work) for all our weekends, games, and discussions about why surgeons are good doctors. I would briefly like to mention all the cool people that I met in France, especially from Lyon and French Texas (Nîmes).

  Loup, and you guys owe me a Monopoly night. Gostaria de agradecer à minha familia, à minha mãe (Ana), ao meu pai (Sérgio), à minha irmã (Jéssica), aos meus avós (Lourdes e Duarte), e ao meu padrinho (Zeca). Obrigado por todo o apoio, não só durante o doutoramento, mas principalmente durante todos os anos que o precederam.Esta tese também é um pouco vossa. Uma menção à Sacha e à Cuca, por estarem lá a cada vez que regresso a casa. Gostava também de agradecer aos meus amigos em Lisboa, do liceu e da FCUL, nomeadamente ao Ruben e ao Miguel pelas sessões de descontração no Steam e pelas deficiências do costume since D. Dinis, e ao João, com quem partilhei a minha primeira visita aos Alpes.

Species Total pe-B pi-B MA pe-B pi-B MA

	C. didactylus	69.7	17.9	49.9	1.94	25.6	71.6	2.8
	T. tetradactyla	1356.7	371.9	911.1	73.7	27.4	67.2	5.4
	M. tridactyla	6579.8	990.4	5589.4	NA	15.1	85.0	NA

Muscle volume in cm 3

	Species	Total	TS	pz-TS	pm-TP	pl-TP	MP	MS	ps-PE	pi-PE	pa-PM	pp-PM
	C. didactylus	332.3	139.8	8.0	19.5	33.6	-	60.4	9.4	14.0	46.50
	T. tetradactyla	2757.8	575.2	153.9	120.2	128.0	307.1	806.1	135.3	59.0	227.9	245.1
	M. tridactyla	12762.2	1718.1	1198.0	510.2	594.1	1592.6	3951.6	1013.6	489.5	851.8	842.8

Masticatory muscle volume (%)

	Species	TS	pz-TS	pm-TP	pl-TP	MP	MS	ps-PE	pi-PE	pa-PM	pp-PM
	C. didactylus	42,2	2,4	5,9	10,1	-	18.2	2,8	4,2	14.0
	T. tetradactyla	20,9	5,6	4,4	4,6	11,1	29,2	4,9	2,1	8,3	8,9
	M. tridactyla	13,5	9,4	4,0	4,7	12,5	31,0	7,9	3,8	6,7	6,6

Table 1 -Modular architectures evaluated with a maximum likelihood method (EMMLi).

 1 Architectures are ordered by number of modules.

	Architecture	Number of modules	Other designations
	I	2	Face-neurocranium 2
	II	3	Hallgrimsson 3
	III	4	Network tetradactyla 4
	IV	5	Rostrum unintegrated
	V	6	Therian 6
	VI	6	Therian 6 zyg-zygpte
	VII	6	Network P. tricuspis
	VIII	6	Hallgrimsson 7(6)
	IX	7	Therian 6 EDMA
	X	7	Hallgrimsson EDMA

Table 3 -Static allometry-corrected modular architectures of 15 myrmecophagous mammals. Number

 3

	of specimens (N), most likely

P. maximus

4; correlation level was similar in O. megalotis and P. maximus). This was more pronounced in Tamandua spp. and M. tridactyla. In Tamandua spp., C. didactylus,

Table 4 -Static allometry-corrected (when detected) integration magnitudes of the oro-nasal (1), naso-palatine (7), and molar-palate (2) modules in myrmecophagous mammals with a 7 module architecture. Values for the interspecific data set are also shown.

 4 Numberof specimens (N), most likely modular architectures (EMMLi), within-module absolute correlations (ρ), and correlation between oro-nasal, and molar-palate modules with the naso-palatine (ρ 1-7, ρ 2-7).

		N EMMM	ρ 1	ρ 7	ρ 2	ρ 1-7	ρ 2-7
	T. tetradactyla T. mexicana	74 IX (7) Li 43 IX (7)	0.58 0.44	0.16 0.19	0.48 0.45	0.26 0.23	0.11 0.13
	M. tridactyla	38 IX (7)	0.61	0.32	0.41	0.28	0.16
	C. didactylus	60 IX (7)	0.65	0.15	0.42	0.17	0.14
	P. maximus	14 IX (7)	0.26	0.26	0.26	-	-
	O. afer	40 X (7)	0.29	0.14	0.40	0.16	0.13
	P. tetradactyla	17 IX* (7)	0.45	0.27	0.33	0.19	0.14
	O. megalotis	8	IX* (7)	0.61	0.50	0.37	-	-
	Interspecific	36 X	0.68	0.28	0.76	0.33	0.41

Table 6 -Evolutionary rates and significance of pairwise comparisons of the face (upper triangle) and neurocranium (lower triangle) modules for allometry-corrected shape data

 6 Atlantogenata. Values for the first two columns correspond to morphological evolutionary rates; remaining values correspond to p-values of pairwise comparisons. Significant p-values are in bold. *significant at α=0.10

		1	2	3	4	5		6		7
	1	0.66/0.68	0.54	0.48	0.27	0.39		0.33		0.33
	2	0.53	0.78/0.78	0.36	0.18	0.37		0.35		0.41
	3	0.47	0.37	0.41/0.41	0.24	0.30		0.34		0.20
	4	0.26	0.19	0.24	0.21/0.22	0.19		0.21		0.24
	5	0.36	0.35	0.29	0.18	0.27/0.28	0.36		0.24
	6	0.31	0.33	0.32	0.21	0.35		0.48/0.52	0.24
	7	0.32	0.41	0.20	0.15	0.23		0.25		0.29/0.28
		R face	R neuro Myr	non-Myr Ver Pho Car Atl	Mar Eua
	Myr	5.41x10 -6	2.27x10 -6	-	0.24	-	-	-	-	-
	non-Myr 2.91x10 -6	1.20x10 -6	0.73	-	-	-	-	-	-
	Ver	1.28x10 -5	3.71x10 -6	-	-	-	<0.01	0.01	0.07*	<0.01	0.06*
	Pho	2.10x10 -6	1.62x10 -6	-	-	0.06*	-	0.68	0.47	0.11	0.94
	Car	2.76x10 -6	1.89x10 -6	-	-	0.11	0.71	-	0.77	0.06*	0.67
	Atl	3.48x10 -6	2.25x10 -6	-	-	0.23	0.39	0.64	-	0.04	0.43
	Mar	5.10x10 -7	4.40x10 -7	-	-	0.01	0.09*	0.07*	0.04	-	0.12
	Eua	2.00x10 -6	1.92x10 -6	-	-	0.29	0.76	0.97	0.75	0.10	-

. R face -evolutionary rate for the face; R neuro; evolutionary rate for the neurocranium; Myr -myrmecophagous; non-Myr -non-myrmecophagous; Ver -Vermilingua; Pho -Pholidota; Car -Carnivora; Atl -

Table S15 . Pairwise comparisons of the allometric trajectory angles for skull shape in P. tricuspis cryptic lineages (HOS)

 S15 . P-values (10.000 iterations) are on the upper triangle and angles between slopes (in degrees) are on the bottom triangle. Significant results written in bold.

		CAF	DHG	GAB	GHA	WAF	WCA
	CAF	-	0.054	1	0.516	0.916	0.061
	DHG	49.453	-	1	0.441	0.522	0.126
	GAB	NA	NA	-	1	1	1
	GHA	63.095	68.940	NA	-	0.911	0.122
	WAF	44.734	59.582	NA	61.804	-	0.101
	WCA	46.947	54.805	NA	77.977	69.995	-

Table S16 . Pairwise comparison of the Procrustes distances between least-squares (LS) means for cryptic lineages (Gaubert et al., 2016)

 S16 . P-values of the difference between the LS means computed with 10,000 iterations (upper triangle) and observed distances (bottom triangle). Significant results are written in bold.

		CAF	DHG	GAB	GHA	WAF	WCA
	CAF	-	<0.001	NA	<0.001	<0.001	0.002
	DHG	0.041	-	NA	0.001	<0.001	0.001
	GAB	NA	NA	-	NA	NA	NA
	GHA	0.049	0.050	NA	-	0.181	0.028
	WAF	0.040	0.047	NA	0.035	-	0.012
	WCA	0.034	0.043	NA	0.043	0.036	-

Table S17 . Pairwise comparison of the Procrustes distances between least-squares (LS) means for three geographical groups

 S17 . P-values of the difference between the LS means computed with 10,000 iterations (upper triangle) and observed distances (bottom triangle). Significant results are written in bold.

		CEN	DHG	WES
	CEN	-	<0.001	<0.001
	DHG	0.040	-	<0.001
	WES	0.037	0.045	-

Table S18 . Pairwise comparison of the allometry-corrected Procrustes distances between least-squares (LS) means for cryptic lineages (Gaubert et al., 2016). P

 S18 -values of the difference between the LS means computed with 10,000 iterations (upper triangle) and observed distances (bottom triangle). Significant results are written in bold.

		CAF	DHG	GAB	GHA	WAF	WCA
	CAF	-	<0.001	NA	<0.001	<0.001	<0.001
	DHG	0.040	-	NA	<0.001	<0.001	0.002
	GAB	NA	NA	-	NA	NA	NA
	GHA	0.048	0.050	NA	-	0.200	0.002
	WAF	0.038	0.046	NA	0.032	-	0.003
	WCA	0.035	0.042	NA	0.045	0.037	-

Table S19 . Pairwise comparison of the allometry corrected Procrustes distances between least-squares (LS) means for three geographical groups

 S19 . P-values of the difference between the LS means computed with 10,000 iterations (upper triangle) and observed distances (bottom triangle). Significant results are written in bold.

		CEN	DHG	WES
	CEN	-	<0.001	<0.001
	DHG	0.038	-	<0.001
	WES	0.036	0.045	-

Table S20 . ANOVA of shape (Procrustes coordinates) ~ log(centroid size)*cryptic lineages (n = 35) in M. javanica.

 S20 Dfdegrees of freedom; Fvalue of F-statistics; *significant p-value.

	48-1325	BMNH	Phataginus tricuspis	Cameroon		Female
	Log(centroid size) Cryptic lineages Log(centroid size):cryptic lineages Residuals Total Number Institution Genus and species 48-1329 BMNH Phataginus tricuspis 12-12-3-1 BMNH Phataginus tricuspis 48-133 BMNH Phataginus tricuspis 12-12-3-3 BMNH Phataginus tricuspis 48-1332 BMNH Phataginus tricuspis 34-11-18-9 BMNH Phataginus tricuspis 77.032-M-0078 RMCA Phataginus tricuspis 34-6-2-92 BMNH Phataginus tricuspis 19138 MfN Phataginus tricuspis 6-3-8-52 BMNH Phataginus tricuspis 37810 MfN Phataginus tricuspis 7-7-8-260 BMNH Phataginus tricuspis 37813 MfN Phataginus tricuspis 1967-980 MNHN Phataginus tricuspis 38099 MfN Phataginus tricuspis 1967-981 MNHN Phataginus tricuspis 75076 MfN Phataginus tricuspis 19624 RMCA Phataginus tricuspis 241130 AMNH Phataginus tricuspis 20206 RMCA Phataginus tricuspis 12-10-28-58 BMNH Phataginus tricuspis 90.042-M-0131 RMCA Phataginus tricuspis 1999-115 BMNH Phataginus tricuspis 83.006-M-0575 RMCA Phataginus tricuspis 20-3-18-42 BMNH Phataginus tricuspis 83.006-M-0585 RMCA Phataginus tricuspis 9075 MfN Phataginus tricuspis 83.006-M-0588 RMCA Phataginus tricuspis 1956-725 MNHN Phataginus tricuspis 90.042-M-0129 RMCA Phataginus tricuspis 1956-724 MNHN Phataginus tricuspis 90.042-M-0132 RMCA Phataginus tricuspis 1956-728 MNHN Phataginus tricuspis 90.042-M-0136 RMCA Phataginus tricuspis MNHN Phataginus tricuspis 90.042-M-0139 RMCA Phataginus tricuspis 439127 USNM Phataginus tricuspis 90.042-M-0142 RMCA Phataginus tricuspis 379617 USNM Phataginus tricuspis 90.042-M-0143 RMCA Phataginus tricuspis 35-10-22-155 BMNH Phataginus tricuspis 90.042-M-0146 RMCA Phataginus tricuspis 35-10-22-157 BMNH Phataginus tricuspis 90.042-M-0157 RMCA Phataginus tricuspis 46-500 BMNH Phataginus tricuspis 90.042-M-0158 RMCA Phataginus tricuspis 70-7-16-1 BMNH Phataginus tricuspis 90.042-M-0162 RMCA Phataginus tricuspis 412726 USNM Phataginus tricuspis 83.006-M-0580 RMCA Phataginus tricuspis 465927 USNM Phataginus tricuspis 90.042-M-0145 RMCA Phataginus tricuspis 465928 USNM Phataginus tricuspis 11490 RMCA Phataginus tricuspis 1990-48 MNHN Phataginus tricuspis 12331 RMCA Phataginus tricuspis 537784 USNM Phataginus tricuspis 12332 RMCA Phataginus tricuspis 537785 USNM Phataginus tricuspis 12543 RMCA Phataginus tricuspis 1-11-21-35 BMNH Phataginus tetradactyla 12544 RMCA Phataginus tricuspis 35-10-22-156 BMNH Phataginus tetradactyla 15907 RMCA Phataginus tricuspis 64-12-1-10 BMNH Phataginus tetradactyla 21668 RMCA Phataginus tricuspis 48-1327 BMNH Phataginus tetradactyla 28686 RMCA Phataginus tricuspis 1942-189 MNHN Phataginus tetradactyla 30808 RMCA Phataginus tricuspis 1958-194 MNHN Phataginus tetradactyla 634 c RMCA Phataginus tricuspis 1962-1174 MNHN Phataginus tetradactyla 6993 RMCA Phataginus tricuspis 14620 RMCA Phataginus tetradactyla 83.006-M-0576 RMCA Phataginus tricuspis 37804 MfN Phataginus tetradactyla 83.006-M-0577 RMCA Phataginus tricuspis 37968 MfN Phataginus tetradactyla 83.006-M-0579 RMCA Phataginus tricuspis 1958-193 MNHN Phataginus tetradactyla 83.006-M-0582 RMCA Phataginus tricuspis 1985-101 MNHN Phataginus tetradactyla 83.006-M-0583 RMCA Phataginus tricuspis 150409 AMNH Phataginus tetradactyla 90.042-M-0133 RMCA Phataginus tricuspis 53868 AMNH Phataginus tetradactyla 90.042-M-0135 RMCA Phataginus tricuspis 53869 AMNH Phataginus tetradactyla 90.042-M-0148 RMCA Phataginus tricuspis 53866 AMNH Phataginus tetradactyla 90.042-M-0150 RMCA Phataginus tricuspis 53870 AMNH Phataginus tetradactyla 90.042-M-0152 RMCA Phataginus tricuspis 53872 AMNH Phataginus tetradactyla 90.042-M-0154 RMCA Phataginus tricuspis 86840 AMNH Phataginus tetradactyla 90.042-M-0156 RMCA Phataginus tricuspis 89399 AMNH Phataginus tetradactyla 90.042-M-0159 RMCA Phataginus tricuspis 220402 USNM Phataginus tetradactyla 90.042-M-0161 RMCA Phataginus tricuspis 481806 USNM Phataginus tetradactyla 90.042-M-0162 RMCA Phataginus tricuspis 481805 USNM Phataginus tetradactyla 56-61 BMNH Phataginus tricuspis 2954 RMCA Smutsia gigantea 1962-2118 MNHN Phataginus tricuspis 12946 RMCA Smutsia gigantea 38506 RMCA Phataginus tricuspis 15320 RMCA Smutsia gigantea 239440 AMNH Phataginus tricuspis 19113 RMCA Smutsia gigantea 450073 USNM Phataginus tricuspis 25479 RMCA Smutsia gigantea 465920 USNM Phataginus tricuspis 27982 RMCA Smutsia gigantea 465924 USNM Phataginus tricuspis 83.006-M-0591 RMCA Smutsia gigantea 465923 USNM Phataginus tricuspis 83.006-M-0592 RMCA Smutsia gigantea 465926 USNM Phataginus tricuspis 35717 RMCA Smutsia gigantea 481811 USNM Phataginus tricuspis 38194 RMCA Smutsia gigantea 481813 USNM Phataginus tricuspis 29-5-29-38 BMNH Smutsia gigantea 481812 USNM Phataginus tricuspis 1913-113 MNHN Smutsia gigantea 38504 RMCA Phataginus tricuspis 53850 AMNH Smutsia gigantea 48-1320 BMNH Phataginus tricuspis 53846 AMNH Smutsia gigantea	Df 1 2 2 29 34 Central African Republic Country Cameroon DR Congo Cameroon DR Congo Cameroon DR Congo Cameroon Uganda Cameroon Uganda Cameroon DR Congo Cameroon Cameroon Central African Republic Equatorial Guinea DR Congo Cameroon (East) DR Congo Nigeria DR Congo Nigeria DR Congo Nigeria DR Congo Togo DR Congo Togo DR Congo Togo DR Congo Togo DR Congo Togo DR Congo Benin DR Congo Nigeria DR Congo Ghana DR Congo Ghana DR Congo Ghana DR Congo Ghana DR Congo Ghana DR Congo Ghana DR Congo Ghana DR Congo Gabon DR Congo DR Congo DR Congo DR Congo DR Congo Equatorial Guinea DR Congo Ghana DR Congo ? DR Congo Cameroon DR Congo Ivory Coast DR Congo Gabon DR Congo Ivory Coast DR Congo DR Congo DR Congo Cameroon DR Congo Equatorial Guinea DR Congo Gabon DR Congo Central African Republic DR Congo ? DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo DR Congo Ivory Coast DR Congo Gabon DR Congo Liberia DR Congo Liberia Sierra Leone DR Congo Ivory Coast DR Congo Liberia DR Congo Liberia DR Congo Ivory Coast DR Congo Ivory Coast DR Congo Ivory Coast DR Congo Ivory Coast DR Congo Ivory Coast ? Liberia Liberia Liberia Ghana Liberia ? Liberia DR Congo Cameroon DR Congo	R 2 0.20 0.07 0.04 0.69	F 8.33 1.41 0.90 --Female Male Sex -Female -? Female ? Male ? -? Male ? ? Male ? Male ? Male ? ? ? Female ? ? ? Female ? Male ? Male ? Female ? Female ? Male ? Female ? Female ? Female ? Female ? Male ? Female ? Female ? Female Female Female Female Male Male ? ? Female ? ? ? Male ? ? ? Female ? Male ? Female ? ? ? ? ? Male ? Female ? ? ? Female ? Female ? Female ? Male ? ? Male ? ? ? Male ? Male ? Male ? Male Male ? ? ? ? ? Female Female Male Male Female ? Male ? Female Female Female ? Female ? Female ? Male Male ? Male ?	p-value <0.001* 0.001* 0.125 --

Table S1 . Resolution of the performed µ-CT scans and scanning platform information. Related to STAR methods. Data S1 1. Anatomical descriptions of myrmecophagous mammals and sister taxa Pygmy anteater (Cyclopes didactylus)

 S1 Myrmecophaga tridactyla (ISEM 065V, MVZ 185238, ISEM 071N). Teeth are segmented in (A) only. Bone is transparent. Dorsal canaliculiorange; mental branchespurple; mandibular canalcyan; teethdark blue. Scale in mm.

	Dasypus novemcinctus	USNM 033867	36.0	RIO
	Proteles cristatus Canis lupus Dasypus novemcinctus Dasypus novemcinctus Dasypus novemcinctus 778N); (L-N) Species Manis crassicaudata Dasypus novemcinctus	Specimen BMNH 34.11.1.5 LACM 23010 LSUMZ 8538 LSUMZ 29160 BMNH 11.10.27.3 BMNH 67.4.12.298 ZMB 84-357	Voxel size (µm) 73.6 600.0 36.0 36.0 58.3 59.2 58.3	, ISEM Scanning platform BMNH -RIO RIO RIO BMNH HZB
	Manis javanica Dasypus novemcinctus	BMNH 9.1.5.858 USNM 020920	49.6 36.0	BMNH RIO
	Orycteropus afer Priodontes maximus	BMNH 27.2.11.113 ZMB 47528	116.5 72.0	BMNH RIO
	Potamogale velox Tapirus indicus	ZMB 71587 KUPRI 506	72.0 625.0(x,y)x300.0(z)	HZB KUPRI
	Tenrec ecaudatus Molossus molossus	Martinez pers. coll. AMNH 234923	69.4 20.0	RIO -
	Rhynchocyon petrsi Talpa europaea	BMNH 55149 Martinez pers. coll.	94.0 89.0	BMNH RIO
	Procavia capensis Cynocephalus volans	UMZC H4980K FMNH 56521	86.0 65.0	--
	Cyclopes didactylus Lemur catta	MNHN 1986-1115 DPC-O92	36.0 100.0	RIO -
	Cyclopes didactylus Tupaia Montana	BMNH 24.12.4.68 FMNH 108831	32.2 40.0	BMNH -
	Tamandua tetradactyla Lepus europaeus	BMNH 34.9.2.196 DMET-LE1	79.8 137.4	NMNH -
	Tamandua tetradactyla Rattus norvegicus	ISEM 788N HACB-RN1	57.1 54.0	RIO -
	Tamandua tetradactyla Dasyurus hallucatus	MVZ 153482 TMM M-6921	45.1 35(x,y)x78(z)	RIO -
	Myrmecophaga tridactyla	ISEM 071 N	79.0	RIO
	Myrmecophaga tridactyla	ISEM 065 V	74.3	RIO
	Myrmecophaga tridactyla	MVZ 185238	63.7	RIO
	Bradypus tridactylus	ZMB 18834	41.7	HZB
	Bradypus tridactylus	MNHN 1999-1065	113.2	RIO
	Choloepus didactylus	ZMB 4949	83.8	HZB
	Choloepus hoffmanni	Hautier pers. coll.	83.9	RIO
	Dasypus pilosus	ZMB 19240	72	HZB

Table S1 -Weight, in grams, of the muscles of the six dissected specimens

 S1

		0.0692	0.0616	0.8789	0.9654	0.9355	6.7043
	TS	0.0977	0.098	0.4761	0.3158	0.4062	2.446
	pz-TS	0.0071	0.0085	0.0799	0.1093	0.1237	0.7373
	pl-TP	0.0156	0.0466	0.1398	NA	0.2594	0.9061
	pm-TP	0.0273	0.0207	0.0794	0.0666	0.1104	0.1783
	TP	0.0429	0.0673	0.2192	NA	0.3698	1.0844
	ps-PE	0.0084	0.0125	0.0837	NA	0.0745	1.2792
	pi-PE	0.0117	NA	0.0319	NA	0.0646	0.5529
	PM	0.0389	NA	0.3079	NA	NA	1.4173
	pe-B	0.0162	NA	0.4135	NA	NA	NA
	pi-B	0.0473	0.0301	1.1378	NA	2.3477	9.5742
	MA	0.0051	0.0127	0.0874	NA	NA	0.3478
	IA	NA	NA	NA	NA	0.3211	NA
	Sg	0.0807	NA	NA	NA	NA	NA
	Mh	0.1005	0.163	NA	NA	NA	NA
	Sm	0.082	0.0787	1.635	NA	NA	5.7758
	SM	NA	NA	2.865	NA	NA	NA
	DN	0.0051	NA	1.1869	NA	NA	1.9974

. Abbreviations for the muscle names are as in the main text. NA -not weighted. Muscle C. did.-1571 C. did. -1525 T. tet. -3075 T. tet. -3074 T. tet. -2813 M. tri. -3023 MS

CurrentBiology 29, 468-475, February 4, 2019

e3 Current Biology 29, 468-475.e1-e3, February 4, 2019

Institut des Sciences de l'Evolution de Montpellier (ISEM), CNRS, IRD, EPHE, Université de Montpellier, Montpellier, France.

------

ACKNOWLEDGMENTS

We thank Steffen Bock, Peter Giere, Frieder Mayer, and Detlef Willborn (MfN); Roberto Portela Miguez, Louise Tomsett, Farah Ahmed, Amin Garbout, and Brett Clark (BMNH); Renaud Lebrun (ISEM/MRI platform), Franc ¸ois Catzeflis, Pierre-Henri Fabre, and Quentin Martinez (ISEM); Guillaume Billet (MNHN); and Chris Conroy (MVZ) for access to collections and assistance with m-CT scanning. We also thank Pierre-Henri Fabre, Chris Emerling, and two anonymous reviewers for helpful comments on the manuscript and Quentin Martinez, M elanie Debiais-Thibaud, and Helder Gomes Rodrigues for fruitful discussions. We acknowledge J.G.M. Thewissen and the North Slope Borough Department of Wildlife Management for Figure S3A. We thank Nelly Pirot, Florence Bernex, and Marion Olive (INSERM) for assistance with histology. Finally, we thank Sarah Jones who helped to improve the English of the manuscript. S.F.-C., L.H. and F.D. were supported by a European Research Council (ERC) consolidator grant (ConvergeAnt #683257). S.F.C. benefitted from the SYNTHESYS Project (Project 312253) founded by the European Community Research Infrastructure Action under the FP7 Integrating Activities Programme. L.H. and F.D. were supported by Centre National de la Recherche Scientifique (CNRS). This work has been supported by ''Investissements d'Avenir'' grants managed by Agence Nationale de la Recherche Labex CEBA (ANR-10-LABX-25-01), Labex CEMEB (ANR-10-LABX-0004), and Labex NUMEV (ANR-10-LABX-0020). This is contribution ISEM 2018-275 of the Institut des Sciences de l'Evolution de Montpellier.

6-Appendices 6.1-Appendix 1

Article 1

Skull shape variation in extant pangolins (Pholidota: Manidae): allometric patterns and systematic implications.

In press: Zoological Journal of the Linnean Society Supplemental information for this article is available in Appendix 1.

SUPPLEMENTAL INFORMATION

Supplemental Information includes four figures, one table, and one data file and can be found with this article online at https://doi.org/10.1016/j.cub. 2018.12.023.

AUTHOR CONTRIBUTIONS

S.F.-C., L.H., and F.D. collected the data, conceived the study, and designed the study. S.F.-C., L.H., and F.D. contributed to discussion and drafted and edited the manuscript. L.H. and F.D. coordinated the study. All authors gave final approval for publication.

DECLARATION OF INTERESTS

The authors declare no competing interest.

Article 3

Comparative anatomy of the facial, masticatory, intermandibular, and hyoid musculatures in anteaters (Vermilingua, Xenarthra) and its implications for the interpretation of morphological convergence in myrmecophagous placentals.

In preparation: to be submitted to PeerJ Supplemental information for this article is available in Appendix 3. skull is further divided into anatomical sub-regions representing smaller modules (Cheverud 1982;Goswami, 2006). Within the smaller cranial modules, it is theoretically possible to envision even smaller modules (e.g., individual bones) until reaching the molecule level. The hierarchical organization of modules is directly related to their dynamism through time [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. Developmental modules undergo temporal transformations, not necessarily associated to their relative timing of occurrence (heterochrony) but rather to their structural integrity from early to late stages of ontogeny [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF]. The totipotent cells from the ventral ectoderm of Drosophila are at the origin of its central nervous system [START_REF] Raff | The shape of life: genes, development, and the evolution of animal form[END_REF].

The expression of the Notch gene causes most of these cells to form neuroblasts that then contribute to the production of neurons [START_REF] Doe | Early events in insect neurogenesis: I. Development and segmental differences in the pattern of neuronal precursor cells[END_REF]. The remaining cells incorporate the hypodermal layer of the skin, resulting in a different functional module. This example not only demonstrates the temporal transformations of the modular structure but highlights the hierarchical nature of modular systems as well as the process of duplication and differentiation underlying the formation of new modules [START_REF] Muller | Novelty in evolution: restructuring the concept[END_REF]Wagner & Altenberg, 1996;Winther, 2001). Modularity, as a result of natural selection, arises through integration and parcellation (Wagner, 1996). If the ancestral state is the presence of poorly correlated morphological traits, modularity originates from integration that will evolve to prevent non-adaptive independent variation (Riedl, 1978); in other words, integration promotes variation of functionally coupled traits, increasing evolvability and reducing adaptively redundant variation (Wagner & Laubichler, 2004). If the ancestral state consists of a highly integrated system, modularity arises by reducing pleiotropic effects among traits belonging to different oral (including two clusters), and masticatory (molar). Using an approach based on Cheverud (1982), Goswami (2006) showed that, as a general rule, the mammalian skull was divided in six morphological modules. These modules consisted of an oral-nasal region, a molar-palate region, the orbit, a zygomaticpterygoid complex, the cranial vault, and the basicranium. More recent research on the integration and modularity in mammals retrieved similar results, with the mammalian skull being typically found to present either two [START_REF] Drake | De telles méthodes peuvent également fournir de nouvelles perspectives sur les patrons développementaux[END_REF][START_REF] Santana | Does nasal echolocation influence the modularity of the mammal skull?[END_REF]Randau et al., 2019), six (Goswami & Finarelli, 2016;Heck et al., 2018;Churchill et al., 2019;Randau et al., 2019). Traits often present different magnitude of correlation (integration) within each of the cranial modules (Goswami, 2006). With the implementation of new methods to test the hypothesis of modularity (Claude, 2008;Klingenberg, 2009;Suzuki, 2013;Adams, 2016;Goswami & Finarelli, 2016) and the increasing accessibility of µCT (micro-computed tomography) scan data and geometric morphometrics hardware and software, research on patterns of integration and modularity have recently blossomed, especially concerning the vertebrate skull (Porto et al., 2009;Goswami & Finarelli, 2016;Simon & Marroig, 2017;Felice & Goswami, 2018;Heck et al., 2018;[START_REF] Hendrick | Morphological diversification under high integration in a hyper diverse mammal clade[END_REF]Churchill et al., 2019;Felice et al., 2019;Randau et al., 2019;Bardua et al., 2019).

Despite the amount of studies focusing on cranial modularity showing some congruence regarding functional and developmental modules, there are still inconsistent results and alternative hypotheses regarding the patterns of morphological modularity across vertebrates. In the context of mammalian cranial modularity, an alternative hypothesis to the six functional/developmental modules (Cheverud, 1982a;Marroig & Cheverud, 2001;Goswami, 2006) is the "Palimpsest model" (Hallgrímsson et al., 2009). Hallgrimsson et al. (2009) put together a set of conceptual and empirical arguments to argue that there is no basis for the partition of the mammalian skull in subsets directly referable to developmental modules. An important difference lies on the definition of integration itself. Hallgrimsson et al. (2009) define integration as "the tendency of a developmental system to produce covariation". They argue that the use of observed correlations as a measure of integration (Goswami, 2006;Porto et al., 2009;Klingenberg, 2009;Goswami & Polly, 2010;Goswami & Finarelli, 2016) is not appropriate. Instead of following the conceptualization of Olson and Miller (1958), they propose a different definition that makes integration independent of the presence of variation, being a property of developmental systems. In et al.'s (2009) conception, integration is a process instead of a pattern (of covariation), consisting of the developmental interactions between sets of traits that confer the potential to induce covariation. As such, covariation structure can be altered without any modification of the developmental Article 4

Hallgrimsson

Patterns of cranial modularity in convergent lineages of ant-eating placentals.

In preparation: to be submitted to BMC Evolutionary Biology Supplemental information for this article is available in Appendix 4.

Modularity

Intraspecific modularity

We used four different methods to assess patterns of modularity within each of the studied species [START_REF] Spurgin | Enamel in the teeth of an embryo edentate (Dasypus novemcinctus linn)[END_REF]. First, we used two exploratory methods without a priori hypotheses (Euclidean Distance Matrix Analysis on non-superimposed landmark configurations -EDMA; Morphological Correlation Network -MCN) to visualize the structure of the data and their raw patterns of covariation and correlation. Secondly, we used two widely used methods to test for a priori hypotheses of modularity (maximum likelihood approach -EMMLi; Covariance Ration -CR).

We used pairwise interlandmark distances to perform EDMA [START_REF] Lele | Euclidean distance matrix analysis: A coordinate-free approach for comparing biological shapes using landmark data[END_REF], in order to detect modular structures while avoiding the potentially undesirable effects of Procrustes superimposition (Cardini, 2019b). EDMA consisted of four steps: (1) reconstruction of the mean shape coordinates obtained from the average form matrix using the 'mEDMA2' function from Claude (2008); other groups that roughly represented skull regions like the cranial vault, the basicranium, and a grouping of landmarks from the occipital and rostrum regions. other seven-module architecture tested (X). In comparison with architecture IX, the landmarks from the maxillary foramen (#4/24) are included in the oro-nasal module. Additionally, the posterior limit of the interpalatine suture (#9) is included in the molar-palate module, while the zygomatic process of the maxilla (#41/52) is integrated with the zygomatic-pterygoid region along with the zygomatic process of the squamosal (#12/30) and the foramen ovale (#13/31). EMMLi retrieved architecture VII, recovered from the MCN analyses of P. tricuspis, for M. pentadactyla, S. gigantea, S. temminckii, P. tricuspis, and P. cristatus (Table 3). These species present a rostral module with landmarks from the oro-nasal region associated to the more posterior landmarks along the naso-frontal sutures (Fig. 1B). They also show a module corresponding to the anterior and posterior parts of the zygomatic arch, and a module that groups the optic foramen (#10/28) and the foramen rotundum (#11/29) with the foramen ovale (#13/31). S. temminckii showed a low posterior probability for this architecture (27%), with architectures III and IV being almost as likely (21% and 25%). M. javanica, the only species for which the number of modules changed after allometric correction, presented the four-module architecture derived from the MCN of T. tetradactyla (III; Table 3). In architecture III, the oro-nasal and molar-palate modules are integrated in a single module. In addition, this architecture differs from the six-module functional hypothesis (V; Goswami, 2006) in having landmarks located along the naso-frontal sutures (#39/50 and #42) grouped with the vault module and in the three most anterior landmarks from the molar-palate region (#3/23 and #5) unintegrated. Architecture III lacks an orbit module, with the landmarks from the optic foramina (#10/28) being clustered with the zygomatic-pterygoid (Fig. S4B). M. crassicaudata presented the least modular skull structure, with only three modules (II;Hallgrimsson, 2004). In M. crassicaudata, the landmarks from the oro-nasal, molar-palate, and anterior part of the orbit grouped in a rostrum module.

The foramen rotundum (#11/29) and the most anterodorsal point of the zygomatic process of the squamosal (#12/30) correlate with those associated to the vault region. The third module is the basicranium, including the foramen ovale and the most posterior point of the interpalatal suture (#9).

EMMLi retrieved a low posterior probability for the skull partition of M. crassicaudata in three modules (21%). Other possibilities found were a different distribution of integration on the same three-module architecture (17%), the two-module face-neurocranium hypothesis (I) with two different distributions of integration between modules (18% and 16%), and the six-module functional hypothesis (16%).

Regarding the integration level (Fig. 3), EMMLi retrieved models for which both M. crassicaudata and P. maximus presented a constant integration level across all modules (ρ = 0.32 and ρ = 0.26, respectively; Table 3). For all other species, the module with the strongest average integration was that corresponding to the oro-nasal region (Tables 2 and3; Fig. 3A). Anteaters presented the highest integration values for this module (0.44 < ρ < 0.65). P. tetradactyla (ρ = 0.49) showed the highest value among pangolins. S. gigantea, which presented a rostrum module including the oro-nasal and naso-frontal regions, also exhibited a relatively high integration (ρ = 0.37). O. megalotis also showed an oro-nasal module as integrated as that of M. tridactyla (ρ = 0.61). S. temminckii showed the least integrated oronasal region (ρ = 0.21). S. gigantea presented the highest integration for the molar-palate module (ρ = 0.53; Table 3), above the average for the remaining species (Table 3; Fig. 3B). Species that showed a seven-module architecture presented a relatively high correlation for this module, as it is composed of only three bilaterally symmetric landmarks. P. cristatus presented the lowest integration level for the molar-palate module (ρ = 0.21).

The orbit module was generally less integrated than the modules from the rostrum. S. gigantea, S.

temminckii, P. tricuspis, M. pentadactyla, and P. cristatus were the exceptions in consistently presenting a relatively well integrated orbit (Tables 2 and3; Fig. 3C). These species all showed the modular pattern

The zygomatic-pterygoid module is poorly integrated, with C. didactylus, and S. gigantea revealing higher than average levels of integration for this module (Table 3; Fig. 3D). O. afer and M.

tridactyla were the species with the lowest integration magnitude (ρ = 0.20) for this module.

The vault was the least integrated module, overall (Tables 2 and3; Fig. 3E). S. gigantea showed an averagely integrated vault (ρ = 0.32). The species with the least integrated cranial vault was T.

tetradactyla (ρ = 0.12).

The basicranium was strongly integrated in T. tetradactyla, M. tridactyla, and O. megalotis (Tables 2 and3; Fig. 3F). Pangolins revealed relatively low integration values of the basicranium, with P. tricuspis presenting the lowest values (ρ = 0.16). C. didactylus also showed a very weakly integrated basicranium (ρ = 0.18). O. afer presented a moderately integrated basicranium.

In species presenting a naso-palatine module, this region was weakly integrated in four of them (Tamandua spp., C. didactylus, and O. afer), moderately integrated in M. tridactyla and P. tetradactyla, and well-integrated in O. megalotis. In all species with different between-module correlations, the nasopalatine module was more strongly correlated with the oro-nasal than with the molar-palate module (Table

The modular partition of the skull obtained from EDMA also showed that landmarks from the anterior and posterior parts of the skull never cluster together. On the other hand, the modules obtained from this method roughly correspond to those recovered with methods relying on Procrustes superimposition (e.g., oro-nasal, basicranium, zygomatic-pterygoid; Fig. S2-3). Our results indicate that, despite the introduction of correlations with no biological meaning, the modular partition of the skull obtained after superimposing landmarks configurations provides comparable results to those of methods avoiding it. Nevertheless, further studies are needed in order to accurately assess the amount of noise introduced by Procrustes superimposition.

Analysis of a priori modular architectures in myrmecophagous mammals Some of the first works that addressed the modular patterns of the skull of mammals used exploratory methods (Cheverud, 1982;Goswami, 2006). However, hypothesis testing methods have become increasingly used, assessing if sets of traits exhibit modular structures when compared to a random organization [START_REF] Klingenberg | Developmental integration in a complex morphological structure: how distinct are the modules in the mouse mandible?[END_REF]Claude, 2008;Klingenberg, 2009a;Adams, 2016).

Using a recently proposed maximum-likelihood approach (EMMLi; Goswami & Finarelli, 2016), we showed that the modular organization of the skull in ant-and termite-eating placental mammals varies between three to seven modules. The species presenting the lowest number of modules (Model II) was also the least sampled (Manis crassicaudata; n = 7). Its modularity pattern probably represents a gross pattern of modularity, as suggested by the inconsistent modular patterning obtained from the hierarchical clustering based on EDMA analyses. The three-module architecture in M. crassicaudata shows a very low posterior probability (0.21), with four other architectures showing values above the 0.05 threshold taken as reference by Goswami and Finarelli (2016). A similar result was obtained for Otocyon megalotis (n = 8), which precludes any further interpretation of the results for these two species.

Most of the species presented a six-(VII) and seven-module (IX and one species with X) architectures. MCN results showed that the basicranium and posterior part of the vault have similar landmark composition of in both P. tricuspis and T. tetradactyla. The structure of these parts of the skull is quite conserved and correspond to those in previously proposed architectures (Cheverud, 1982;Hallgrímsson et al., 2004;Goswami, 2006). These regions originate from the mesoderm in the very early stages of skull development (e.g., Piekarski et al., 2014;[START_REF] Hallgrímsson | Integration and the developmental genetics of allometry[END_REF]. In addition to their common tissue origin, covariance-generating processes such as muscle-bone interaction, tooth eruption, 2006; Parr et al., 2016;Heck et al., 2018;Churchill et al., 2019;Randau, Sanfelice, & Goswami, 2019).

Given that the skull and the masticatory apparatus perform virtually the same functions across tetrapods (Schwenk, 2000), especially in mammals (Hiiemae, 2000), the maintenance of a functional partition of the skull across all mammals is beneficial in promoting the evolvability of functionally related structures (Riedl, 1978;Wagner & Altenberg, 1996). Anteaters are a good example of modular conservatism, with the giant (M. tridactyla) and the pigmy (C. didactylus) anteaters showing completely different skull shapes (Fig. 4), but a similar sevenmodule cranial architecture (IX). In fact, considerable shape change can occur while phenotypic modularity patterns are maintained, as a result of extreme directional selection acting on conserved partitions [START_REF] Parsons | Conserved but flexible modularity in the zebrafish skull: implications for craniofacial evolvability[END_REF]. Our projection of the covariance matrices of our 15 myrmecophagous species showed that most species present quite conserved patterns of phenotypic covariation (Fig. 6). With the exception of T. tetradactyla, M. javanica, S. temminckii, S. gigantea, and M. tridactyla, most species cluster in a relatively small phenotypic covariation morphospace. These results are in line with EMMLi output in which the majority of the architectures fall within the expected variation reported among mammals (e.g., Goswami, 2006;Porto et al., 2009). Curiously, the two closely related (Gibb et al., 2016) and morphologically similar (Wetzel, 1975) T. tetradactyla and T. mexicana were apart in the phenotypic covariation morphospace. This might reflect the more pronounced intramodular integration in the oronasal, orbit, and basicranium region displayed by T. tetradactyla (Tables 2 and3).

Nevertheless, our results suggest that extreme rostrum elongation and tooth loss might have affected covariance patterns in Tamandua and Myrmecophaga. The naso-palatine landmarks are more correlated to the oro-nasal than to the molar or orbit landmarks, in both genera. On the contrary, the nasopalatine module is more correlated with the molar-palate module, in the interspecific dataset. In O. afer, P. maximus, or C. didactylus the correlations between nasal-palatine and the other rostrum modules are not substantially different (Table 4).

Concerning the modular organization of the zygomatic-pterygoid region, we found a conserved zygomatic arch module in P. cristatus, O. afer, as well as in the maximum-likelihood model selection performed with the interspecific dataset. This is congruent with the role of this structure as the origin for part of the mandibular adductor musculature. Despite being myrmecophagous, P. cristatus and O. afer retain active mastication and biting functions (Patterson, 1975;[START_REF] Anderson | Functional analysis of the feeding apparatus and digestive tract anatomy of the aardwolf Proteles cristatus[END_REF].

However, the connection between modularity and function is not straightforward, exemplified by the presence of a zygomatic arch module in four pangolins (P. tricuspis, Smutsia spp. and M. pentadactyla).

proxies for modularity and integration, we propose the following set of complementary possibilities to explain our results: 1) The genetic and developmental basis of the placental skull are extremely conserved, hindering drastic changes in modularity patterns even under strong selective pressures or eventual minor mutations (canalization); 2) Under a canalization scenario, limited axes of variation are available for the phenotype; these axes, under specific selective pressures, may generate extreme trait covariation/correlation (i.e., integration) of functionally related traits, while preserving phenotypic organizational modules [START_REF] Cardini | Larger mammals have longer faces because of size-related constraints on skull form[END_REF][START_REF] Parsons | Conserved but flexible modularity in the zebrafish skull: implications for craniofacial evolvability[END_REF]Felice et al., 2019); 3) Anteaters represent an exception, showing a putative a new module with differing variance direction (e.g., nasopalatine module in myrmecophagid anteaters). We interpret the anteater example as decanalization (Waddington, 1953;[START_REF] Stern | Selection for subthreshold differences and the origin of pseudoexogenous adaptations[END_REF] resulting from strong selective pressures and extreme ecological specialization.

Under the complementary paths 1) and 2), we would assume that myrmecophagy could have driven to changes of correlation in the functional modules of the rostrum. In this case, our data fails to detect a convergent shift among myrmecophagous placentals. However, changes in the morphospace and adaptation to functionally demanding ecologies (e.g., fossoriality) do not mandatorily impact structural integration [START_REF] Sansalone | Impact of transition to a subterranean lifestyle on morphological disparity and integration in talpid moles (Mammalia, Talpidae)[END_REF].

Under scenario 3), we can consider that the interaction between the nasal-frontal and maxillarypalatine condensations might represent a sub-module that has shifted from being correlated to the molarpalate module in placentals, to a sub-module of the oro-nasal. In the case of most pangolins and P.

cristatus, only the naso-frontal region shows this shift. Our results might indicate that long-snouted myrmecophagous placentals tend to preserve modularity patterns associated to developmental processes occurring early in ontogeny (orofacial growth ;[START_REF] Zelditch | Ontogenetic variation in patterns of phenotypic integration in the laboratory rat[END_REF]Zelditch & Carmichael, 1989) both due to reduced covariance generated by occlusion and to the pronounced variation generated by the allometric growth of the rostrum.

Supplemental information to

Supplemental tables

Table S1. Definitions of the 75 cranial landmarks used.

Numbers Definition

Appendix S2

Common traits of the African pangolins:

-The vomer protrudes through the inter-maxillary suture and is visible in the palate (in M. crassicaudata this also

PTA analysis

Materials and methods

We performed a phenotypic trajectory analysis (PTA) to compare the direction and length of the trajectories between juveniles and adults of all species in the morphospace (Adams and Collyer 2009;Collyer and Adams 2013). Adults and juveniles were defined as the specimens presenting a centroid size above the third quartile and below the first quartile, respectively. Specimens with intermediate centroid size values were excluded to prevent errors in the attribution of age categories. Significance of phenotypic trajectory lengths and angles was assessed with a pairwise comparison between groups. The PTA was only performed on the interspecific dataset.

Results

The PTA (50.06% explained variance; Fig S2) retrieves a significant effect of species (F6,111 = 28.34, p < 0.001), age (derived from centroid size; F1,111 = 27.03, p < 0.001), and the interaction between the two factors (F6,111 = 1.51, p < 0.001) on shape.

Pairwise comparisons between the angles of the trajectories do not significantly differ between most species, with the exception of Phataginus tricuspis that presents a significantly different trajectory angle compared to Manis pentadactyla and Manis javanica (Table S4). Manis crassicaudata and Smutsia gigantea show a significantly longer trajectory than all other species (Table S4). These two species are the largest species, in average, implying an increase of either growth rate or a growth time (Fig. S2). Given that some species are relatively rare in museum collections (e.g., M. crassicaudata), trajectory length must be interpreted with caution, as sampling is not homogeneous across all developmental stages.

Allometry-corrected analysis of the interspecific dataset

Results

A Procrustes ANOVA performed on the allometry-corrected shapes reveals that species present different skull shapes (F6,166 = 50.35, p < 0.001; Table S12). Pairwise comparisons showed that all species presented significantly different skull shapes (Table S13). The first axis of the PCA explains 32.3% and the split between African and Asian species is less evident when compared to the PCA on raw Procrustes coordinates (Fig. 6A), with Smutsia spp and M. javanica presenting overlapping values (Fig. S3A). Asian species are characterized by positive PCres1 values, while the African species present either negative (Phataginus spp.) or positive (Smutsia spp.) values. Morphologically, specimens with positive values present a wider and more robust skull, with the zygomatic processes of the maxillae projecting posteriorly until half length of the orbit. M. pentadactyla is by far the species scoring higher values, followed by M. crassicaudata and M. javanica. The latter presents PCres1 values similar to those of Smutsia species. P. tetradactyla presents the lowest PCres1 values, while P. tricuspis presents a wide range of negative values (Fig. S3). PCres2 (16.2%) separates specimens with a long rostrum (positive values) from those with a relatively small rostrum (negative values). Thus, M. javanica shows the highest values PCres2 values, while S. temminckii presents the lowest (Fig. S3). S. gigantea scores PCres2 values overlapping those of S. temminckii, while all other species occupy a morphospace in between. PCres3 shows a similar pattern to the one observed in Fig. 6B, showing a relatively low effect of size on the traits explained by this axis (Table S14).

The allometric-correction did not influence the a posteriori attribution rates of the LDA performed on the PCress explaining 90% of the variance, when compared to the results using the raw Procrustes data (Data S3).

Discussion

When compared to the analysis with the raw Procrustes coordinates, the main change in the morphospace relates to the first and second axes. The morphospace and the Procrustes distances between the LS means showed that, when allometry is accounted for, S. gigantea occupies a radically different morphospace, compared to the Asian pangolins (Fig. S3), in particular to M. javanica, to which it resembled when size was not taken into account (Fig. 6). When the data was corrected for allometry, S. gigantea occupies a morphospace that is much closer to its sister taxon, S. temminckii. We showed that allometry adds noise when considering the intrageneric relationships within Smutsia.

Allometry-corrected analysis of the P. tricuspis dataset

Results

A Procrustes ANOVA performed on the allometry-corrected shapes reveals that cryptic lineages present different skull shapes (F4,65 = 3.77, p < 0.001; Table 12). Pairwise comparisons showed that all tested cryptic lineages presented significantly different skull shapes except for Ghana (GHA) and Western Africa (WAF; Table S18). Gabon (GAB) was not tested due to lack of replicates. Globally, the morphospace did not change significantly when compared to the PCA performed on the raw Procrustes coordinates (Fig. 5). PCres1 (14.9%) roughly segregates CAF (negative values) from WAF-GHA (positive values), with both DHG and WCA skulls scoring values in between (Fig. S6). DHG specimens present a wide range of PCres1 values, ranging from the most negative to positive values close to WAF and GHA. PCres2 (10.3%) range of values are also similar to the PCA on raw Procrustes data, except for the WCA skulls, which score slightly higher values, on average (Fig. S6A). PCres3 (6.0%) values are higher for WAF-GHA skull when allometry is taken into account. Nevertheless, this difference is slight and this axis does not efficiently segregate between cryptic species. The specimen from Gabon occupies a similar morphospace as described for the raw Procrustes coordinates (see 'Results: Intraspecific variation within P. tricuspis').

The allometric-correction had a noticeable influence on the a posteriori attribution rates of the LDA performed on the PCress explaining 90% of the variance, when compared to the analysis on the raw Procrustes data (Data S3). Allometric correction increased the a posteriori attribution rates from 75.4% to 82.9%. However, the incorrect attributions occurred mostly between CAF-WCA and WAF-GHA as described in the analysis of the raw Procrustes coordinates (Data S3). Therefore, a cross-validated LDA was performed with the same three regional groups.

A Procrustes ANOVA revealed a significant effect of the division of P. tricuspis in three morphological groups, WES, DHG and CEN (F2,67 = 5.01, p < 0.001; Table S12). Pairwise comparisons showed that all groups presented significantly different skull shapes (Table S19). This shows that size did not influence the segregations of the skull of the three groups based on skull shape. While

Manis javanica cryptic lineages

Methods

Intraspecific variation within Manis javanica: A third subset including adult M. javanica specimens with known locations (n=25) was used and we applied the same procedure as for P. tricuspis (see 'Materials and methods') in order to investigate intraspecific geographical variations in skull shape. The genetic clusters from Nash et al. (2018) were used: Sumatra / Singapore (Sumatra, Thailand and Burma), Java (Java and Bali), and Borneo.

Given that the genetic clusters in M. javanica present very similar slopes (Fig. S7), allometry-corrected residuals were obtained from a multiple regression of shape coordinates against size (i.e., shape~log(size)).

Results

Using the main groups identified by Nash et al. (2018) as categories, an ANOVA yields a significant effect of logarithm transformed centroid size (F1,29 = 8.33, p < 0.001) and geographical distribution (F2,29 = 1.41, p < 0.001; Table S20). The effect of the interaction between both variables (F2,29 = 0.90, p = 0.125) is not significant, indicating that the slopes for the three groups (Sumatra / Singapore, Java, and Borneo) are parallel (Fig. S9). Procrustes ANOVAs revealed that skull shape significantly differ between cryptic lineages (F2,22 = 2.12, p < 0.001; Table S12). However, this difference was not significant when allometry was taken into account (F2,22 = 1.13, p = 0.225). Therefore, we describe only the PCA performed on the raw Procrustes coordinates. PC1 (15.4%) positively correlates with rostrum length, palatine width, a short posterior projections of the maxillae on the palatines, and a relatively small braincase with a dorsal basioccipital compared to the palate (Fig. S8).

Skulls from Java score negative values, while specimens from Sumatra/Singapore show a range of negative and positive values, on average higher. The only three skulls from Borneo score, on average, the highest PC1 scores. PC2 (12.0%) and PC3 (9.8%) appear to explain shape changes associated to ontogenetic allometry (see 'Results: Allometry within extant pangolins'), and do not segregate between cryptic lineages. We interpret the small range of PC2-3 values of the Borneo lineage as a result of the low sampling.

Discussion

Our results on skull shape variation in M. javanica are not conclusive regarding the recognition of cryptic lineages, as we did not retrieve significant differences among the potential groups defined by Nash et al. (2018). Differences between groups are appear to separate Sumatra/Singapore from Java (Fig. S8). However, differences between genetic clusters are non-significant when allometry-corrected shapes are considered. The existence of at least two divergent mitochondrial lineages within M.

javanica was recently described by Zhang et al. (2015). If our sample size is clearly insufficient, the lack of evidence for the differentiation of skull morphologies between the three M. javanica lineages may be a result of introgressions, exemplified by sample from Java showing evidence of introgression from Singapore/Sumatra and Borneo (Nash et al., 2018). Additionally, the divergence time for cryptic lineages within M. javanica (0.4 -2.5 Mya; TMRCA of M. javanica-M. culionensis) is likely more recent compared to the split between Western and Central African lineages within P. tricuspis (0.8 -4.6 Mya;[START_REF] Gaudin | Appendix 6 Extended abstract in French[END_REF]. Additional sampling effort on the Sunda and Philippine pangolins is key to unveil a putative morphological disparity within South-East Asian pangolins.

6.4-Appendix 4

Supplemental information to Article 4