domain: sdu sdv

text:
Kévin Rey
email: kevin.rey@wits.ac.za

Michael O Day

Romain Amiot

François Fourel

Julie Luyt

Marc J Van Den Brandt

Christophe Lécuyer

Bruce S Rubidge

Oxygen isotopes and ecological inferences of Permian (Guadalupian) tetrapods from the main Karoo Basin of South Africa

Keywords: PALAEO Anteosaurus, pareiasaur, Paleoecology, Phosphate apatite, Abrahamskraal Formation

The Abrahamskraal Formation of South Africa has a diverse middle Permian (Guadalupian) fossil tetrapod fauna comprising largely basal therapsids and pareiasaurian parareptiles.

Knowledge on the paleoecology of these animals is limited because inferences of many ecological traits in mid-Permian tetrapods are based on deductions from morphology. While it is widely accepted that the rhinesuchid amphibians were aquatic, the ecological lifestyle of pareiasaurs and dinocephalian therapsids remains uncertain. To investigate the ecological roles of different middle Permian tetrapod taxa we studied stable oxygen isotope compositions of phosphate from teeth and bones as a proxy for water dependence. Our results reveal similar δ 18 O p values for pareiasaurs, the dinocephalian Anteosaurus, and therocephalians, with a range of values similar to those of extant terrestrial species. The consistent δ 18 O p values for pareiasaurs strengthen our interpretation of a terrestrial lifestyle for these parareptiles, but the lower Anteosaurus δ 18 O p values might question the interpretation and a larger sample size may result in a more conclusive outcome. These results conclude the debate on the ecology of middle Permian pareiasaurs. A terrestrial lifestyle is applicable only to the middle Permian species and a different lifestyle is possible for pareiasaurs species that lived after the end Capitanian extinction.

Introduction

The rich tetrapod fauna from the Abrahamskraal Formation of South Africa provides a unique window onto high latitude fauna of Gondwana during the middle Permian (Guadalupian). One of its major constituent taxa, dinocephalian therapsids, achieved widespread distribution across Pangaea [START_REF] Cisneros | Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea[END_REF][START_REF] Liu | Osteology, ontogeny, and phylogenetic position of Sinophoneus yumenensis (Therapsida, Dinocephalia) from the Middle Permian Dashankou Fauna of China[END_REF][START_REF] Golubev | Dinocephalian stage in the history of the Permian tetrapod fauna of Eastern Europe[END_REF]; other well-represented groups, including dicynodont therapsids, rhinesuchid temnospondyls and pareiasaurian parareptiles, were restricted to Gondwana at this time [START_REF] Golubev | Permian tetrapod stratigraphy[END_REF][START_REF] Fröbisch | Composition and similarity of global anomodont-bearing tetrapod faunas[END_REF][START_REF] Kurkin | Permian anomodonts: paleobiogeography and distribution of the group[END_REF]. The fauna is best known from the Capitanian-aged Tapinocephalus Assemblage Zone from the upper Abrahamskraal Formation, which is terminated by the extinction of 75-80% of tetrapod species, including all dinocephalians at a global scale and all Guadalupian pareiasaur species at a local scale [START_REF] Day | When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa[END_REF].

The causes of the Capitanian mass extinction event are unclear with several hypotheses proposed such as the Emeishan volcanism [START_REF] Zhou | A temporal link between the Emeishan large igneous province (SW China) and the end-Guadalupian mass extinction[END_REF][START_REF] Wignall | Volcanism, mass extinction, and carbon isotope fluctuations in the Middle Permian of China[END_REF]Bond and Wignall, 2014), marine anoxia [START_REF] Jin | Two phases of the end-Permian mass extinction[END_REF][START_REF] Hallam | Mass extinctions and sea-level changes[END_REF][START_REF] Isozaki | Rapid sea-level change in the Late Guadalupian (Permian) on the Tethyan side of South China: litho-and biostratigraphy of the Chaotian section in Sichuan[END_REF][START_REF] Saitoh | The appearance of an oxygen-depleted condition on the Capitanian disphotic slope/basin in South China: Middle-Upper Permian stratigraphy at Chaotian in northern Sichuan[END_REF], global marine regression or even the release of methane in the atmosphere (Krull et al., 2000;Krull and Retallack, 2000;[START_REF] Retallack | Methane release from igneous intrusion of coal during Late Permian extinction events[END_REF][START_REF] Svensen | Siberian gas venting and the end-Permian environmental crisis[END_REF]. Although most of these causes have been either questioned (Bond et al., 2010;[START_REF] Sheldon | Contrasting geochemical signatures on land from the Middle and Late Permian extinction events[END_REF] or might not have had impact on the continental fauna and flora [START_REF] Sheldon | Contrasting geochemical signatures on land from the Middle and Late Permian extinction events[END_REF], with the possible exception of the volcanism in South China [START_REF] Day | When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa[END_REF], conditions in the southwestern Karoo Basin may have been exacerbated by regional aridification resulting from tectonic activity to the south [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF]. Clues to the causes, as well as to the question of how ecosystems react to different forms of disruption, can be found in the ecological characters of individual species and their place within food webs. While the lifestyle and ecological niche occupation of some species can be inferred from morphological characters (Canoville and Laurin, 2010;Canoville and Chinsamy, 2015;[START_REF] Jasinoski | Comparative feeding biomechanics of Lystrosaurus and the generalized dicynodont Oudenodon[END_REF], this is not true for all tetrapods. Incompletely preserved skeletons lacking key parts of the anatomy, the presence of characters that are not known in extant tetrapods, or discrepancies between ecological deductions from morphology and other disciplines can all lead to uncertainty (Canoville and Chinsamy, 2017).

The pareiasaurs and dinocephalians that succumbed to the Capitanian mass extinction appear to differ in a few ecological characters: they have very disparate dentition, suggesting that the herbivores consumed different types of vegetation, and their skeletons are usually preserved under different taphonomic conditions (Boonstra, 1969), suggesting different lifestyles. The lifestyle of pareiasaurs in particular has been variously interpreted, when not inconclusive (Canoville and Chinsamy, 2017;[START_REF] Boitsova | Evolution of humeral microanatomy and lifestyle in amniotes, and some comments on palaeobiological inferences[END_REF], as completely aquatic [START_REF] Case | Environment of tetrapod life in the late Paleozoic of regions other than North America[END_REF][START_REF] Ivakhnenko | Tetrapods from the east european placket-Late Paleozoic natural territorial complex[END_REF]), amphibious (Boonstra, 1969;[START_REF] Ochev | Materials to the tetrapod history at the Paleozoic-Mesozoic boundary[END_REF][START_REF] Khlyupin | Cemetery of the Permian reptiles[END_REF][START_REF] Kriloff | Evolution of bone microanatomy of the tetrapod tibia and its use in palaeobiological inference[END_REF], or terrestrial [START_REF] Voigt | Tetrapod footprints from the uppermost level of the Permian Ikakern Formation (Argana Basin, Western High Atlas, Morocco)[END_REF][START_REF] Benton | Preservation of exceptional vertebrate assemblages in Middle Permian fluviolacustrine mudstones of Kotel'nich, Russia: stratigraphy, sedimentology, and taphonomy[END_REF][START_REF] Canoville | Insights into the habitat of Middle Permian pareiasaurs (Parareptilia) from preliminary isotopic analyses[END_REF][START_REF] Verrière | Assessing the completeness of the fossil record: comparison of different methods applied to parareptilian tetrapods (Vertebrata: Sauropsida)[END_REF]. Similarly, the dinocephalian Anteosaurus, while generally accepted to have been a fully terrestrial animal [START_REF] Nicolas | Changes in Permo-Triassic terrestrial tetrapod ecological representation in the Beaufort Group (Karoo Supergroup) of South Africa[END_REF][START_REF] Kammerer | Systematics of the Anteosauria (Therapsida: Dinocephalia)[END_REF][START_REF] Kemp | The origin and radiation of Therapsids[END_REF][START_REF] Canoville | Insights into the habitat of Middle Permian pareiasaurs (Parareptilia) from preliminary isotopic analyses[END_REF], has also been considered to have been riparian (Boonstra, 1955(Boonstra, , 1962)), or even amphibious [START_REF] Ivakhnenko | Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe[END_REF].

Stable isotopic studies of hard tissues are useful to determine certain lifestyle aspects of animals. For instance, this technique can be used to reconstruct the relationship of an individual to aquatic environments. Stable oxygen isotope composition (δ 18 O) of vertebrate apatite is correlated to both body temperature and to the oxygen isotope composition of body water (δ 18 O bw ), which is mostly derived from the consumption of either meteoric water or plant water, or a combination of both [START_REF] D'angela | Evolutionary rates of mid-Permian tetrapods from South Africa and the role of temporal resolution in turnover reconstruction[END_REF][START_REF] Kohn | Predicting animal δ 18 O: Accounting for diet and physiological adaptation[END_REF]. Once ingested this water undergoes fractionation, mostly caused by transcutaneous evaporation, urine and faeces [START_REF] Luz | Oxygen isotope variations in phosphate of biogenic apatites, IV. Mammal teeth and bones[END_REF]Bryant and Froelich, 1995;[START_REF] Amiot | Oxygen isotope fractionation between crocodilian phosphate and water[END_REF].

Fractionation, which increases 18 O in the remaining body water, is therefore more intense for species which do not replenish their body water by drinking often [START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF] and less intense when transcutaneous evaporation is reduced as a result of an aquatic or semiaquatic lifestyle [START_REF] Clementz | Identifying Aquatic Habits Of Herbivorous Mammals Through Stable Isotope Analysis[END_REF][START_REF] Amiot | Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods[END_REF]. Consequently, for extant mammals, species which consume large quantities of water, or spend much time in water, have lower δ 18 O bw values than those with a strict terrestrial ecology and only consume plants [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF][START_REF] Kohn | Herbivore tooth oxygen isotope compositions: Effects of diet and physiology[END_REF][START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF]. For example, two studies dedicated to the isotopic analysis of mammals from national parks in Kenya have shown that the δ 18 O values recorded in the apatite of extant hippopotamus are lower than those of coexisting terrestrial mammals such as lions, elephants and even waterbuck. Depending on the water-dependence of the terrestrial species (i.e. obligate drinkers or not), the δ 18 O values of the hippopotamus are about 3‰ lower than those of water-dependent animals and the difference can be as high as 7‰ when compared with water-independent species [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF][START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF]Fig. 1; Table 1). The δ 18 O values of the semi-aquatic hippopotamus, when compared with the δ 18 O values of ingested water, fit between the equations for terrestrial placental mammals [START_REF] Amiot | Latitudinal temperature gradient during the Cretaceous Upper Campanian-Middle Maastrichtian: δ 18 O record of continental vertebrates[END_REF], those for crocodilians [START_REF] Amiot | Oxygen isotope fractionation between crocodilian phosphate and water[END_REF] and freshwater turtles (modified from [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF]Fig. 1). A more complete review of δ 18 O values for hippopotamus and co-existing vertebrates has been compiled from extant and fossil individuals [START_REF] Clementz | Identifying Aquatic Habits Of Herbivorous Mammals Through Stable Isotope Analysis[END_REF] showing constant lower values for the semi-aquatic hippopotamus. Accordingly, by comparing the apatite δ 18 O values of various co-existing vertebrates of contrasting lifestyles, it should be possible to interpret the ecology of extinct taxa as has been done by [START_REF] Amiot | Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods[END_REF] for spinosaurid dinosaurs.

In an earlier study [START_REF] Canoville | Insights into the habitat of Middle Permian pareiasaurs (Parareptilia) from preliminary isotopic analyses[END_REF], while undertaking research on the ecology of pareiasaurs, pointed out that most of the dinocephalians had lower oxygen isotope compositions than the rest of the tetrapod sample; however, they still interpreted dinocephalians to be fully terrestrial based on the standard deviation of their values. [START_REF] Rey | Global climate perturbations during the Permo-Triassic mass extinctions recorded by continental tetrapods from South Africa[END_REF] also concluded that the Guadalupian pareiasaurs were fully terrestrial, but their conclusions were only tentative as their study was undertaken on a small sample size derived from specimens curated in different museum collections in South Africa. To clarify this point, and to strengthen our comparisons, we have increased our sample size of dinocephalians, pareiasaurs and other taxa, and measured the carbon and oxygen isotope compositions of apatite carbonate as well as the phosphate oxygen isotope compositions of both bones and teeth.

Material and methods

Sample collection

A feature of this isotope study, apart from being the most taxonomically extensive yet undertaken in the Abrahamskraal Formation, is that the tetrapod fossils sampled are well provenanced and come from a number of different lithostratigraphic members in stratigraphic succession. This is the first time that such a stratigraphically controlled isotope study has been undertaken in the Abrahamskraal Formation, but has the disadvantage that for some of the stratigraphic members only a few specimens of particular taxa were found. Bone apatite of twenty-six tetrapod fossils were sampled, and for seventeen of them teeth were also sampled.

All samples were analysed for their stable oxygen isotope composition of apatite phosphate and carbonate. The fossils were recovered from eight localities within a radius of 100 km in the Main Karoo Basin, between 21.0° and 22.1° of latitude and -32.9 and -32.2° of longitude (Fig. 2; Supplementary Table 1), and are curated in the collection of the Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg. Most specimens were collected by the authors of this study and are characterized by a secure taxonomic identification.

All sampled fossils were collected from horizons belonging to the Abrahamskraal Formation, which is subdivided into eight members respectively named from the lowest to the highest: Combrinkskraal, an unnamed member, Grootfontein, Leeuvlei, Koornplaats, Swaerskraal, Moordenaars and Karelskraal members [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF]. To compensate as much as possible for temporal variations in isotopic values, we combined the localities from stratigraphically equivalent horizons (Supplementary Table 1) which were divided into three time bins. The lowest (one locality) corresponds to the upper Leeuvlei Member, the middle bin combines four localities from the lower to lower-middle Moordenaars Member and one between the upper Koornplaats and lower Moordenaars members, and the uppermost bin combines two localities from the overlying Karelskraal Member.

Sample sizes were severely limited by the availability of species from specific geological horizons and, due to the destructive and targeted nature of sampling for stable isotope analysis, the availability of suitable specimens with appropriate and reliable taxonomic data. The sample collection assembled for this study included one rhinesuchid amphibian, twelve therapsids, and thirteen pareiasaurs. The therapsid sample-set comprises ten dinocephaliansfive Titanosuchidae indet., one tapinocephalid (Criocephalosaurus sp.), and four Anteosaurus magnificusand two therocephalians (Glanosuchus sp. specimens). In South Africa, four pareiasaur species have been recognized from the middle Permian:

Bradysaurus baini, B. seeleyi, Embrithosaurus schwarzi and Nochelesaurus alexanderi [START_REF] Lee | A taxonomic revision of pareiasaurian reptiles: implications for Permian terrestrial palaeoecology[END_REF][START_REF] Van Den Brandt | Cranial morphology and phylogenetic relationships of the Middle Permian pareiasaur Embrithosaurus schwarzi from the Karoo Basin of South Africa[END_REF]. As the pareiasaur specimens sampled are not all well preserved, only six could be reliably identified with three Bradysaurus bainii, two

Embrithosaurus schwarzi and one Nochelesaurus alexanderi; the remaining seven specimens cannot be identified to genus and are referable only to the family level (pers. com. M. Van den Brandt; see Supplementary Table 1).

Apart from the above specimens we collected, fossil data obtained from the De Bad locality were also included [START_REF] Rey | Global climate perturbations during the Permo-Triassic mass extinctions recorded by continental tetrapods from South Africa[END_REF][START_REF] Rey | Oxygen isotopes suggest elevated thermometabolism within multiple Permo-Triassic therapsid clades[END_REF]. This sample collection comprises six dinocephalianstwo Criocephalosaurus, one addition tapinocephalid (either Mormosaurus

or Struthiocephalus), one Titanosuchidae indet., two Anteosaurusone therocephalian (Glanosuchus), and two pareiasaurs (one Bradysaurus baini and one unidentified).

To obviate biases resulting from environmental change over time, the stable isotope oxygen of phosphate apatite (δ 18 O p ) and the stable isotope carbon of carbonate apatite (δ 13 C c ) boxplots obtained per taxon were plotted against their respective stratigraphic members (Figs.

5 and 6).

Analytical techniques

The phosphate radical is of interest as the molecular bond is stronger than that of carbonate and inorganic alteration at low temperature has little effect on their δ 18 O p values [START_REF] Lécuyer | Oxygen isotope exchange between dissolved phosphate and water at temperatures ≤135°C: inorganic versus biological fractionations[END_REF]. Comparison between the phosphate and carbonate values allows us to potentially detect isotopic compositions of diagenetic origin [START_REF] Iacumin | Oxygen isotope analyses of coexisting carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate?[END_REF]. In order to measure the oxygen isotope composition of the apatite phosphate radicals, we isolated these ions using acid dissolution and anion-exchange resin applying a standard protocol [START_REF] Lécuyer | Oxygen isotope analysis of phosphate[END_REF]. Once quantitatively precipitated in a thermostatic bath set at a temperature of 70 °C, the silver phosphate was filtered, washed with double deionized water, and dried at 50 °C.

Oxygen isotope compositions of the powders were measured using a high-temperature pyrolysis technique involving a VarioPYROcube TM elemental analyzer (EA) interfaced in continuous flow (CF) mode to an Isoprime TM isotopic ratio mass spectrometer (IRMS) (EA-Py-CF-IRMS technique) at the Laboratoire de Géologie de Lyon (UMR 5276, Université Claude Bernard Lyon 1). For each sample, five aliquots of 300 μg of Ag 3 PO 4 were mixed with 300 μg of pure graphite powder and loaded in silver foil capsules.

Pyrolysis was performed at 1450 °C. Measurements were calibrated against the NBS120c (natural Miocene phosphorite from Florida: δ 18 O = 21.7‰; [START_REF] Lécuyer | Thermal excursions in the ocean at the Cretaceous-Tertiary boundary (northern Morocco): δ 18 O record of phosphatic fish debris[END_REF])

and the NBS127 (barium sulfate, BaSO 4 : δ 18 O = 9.3‰; [START_REF] Hut | Consultants' group meeting on stable isotope reference samples for geochemical and hydrological investigations[END_REF]. Silver phosphate samples precipitated from standard NBS120c were repeatedly analysed (δ 18 O p = 21.7‰; 1σ = 0.3; n = 12) along with the silver phosphate samples derived from fossil bioapatites to ensure that no isotopic fractionation occurred during the wet chemistry. Data are reported as δ 18 O p values vs.

V-SMOW (in ‰ δ units).

About 10 mg of tooth or bone powder was pre-treated [START_REF] Koch | The effects of sample treatment and diagenesis on the isotopic integrity of carbonate in biogenic hydroxylapatite[END_REF] for the carbon and oxygen isotopic compositions of apatite carbonate is better than ±0.15‰ and ±0.20‰, respectively. The carbon and oxygen isotopic compositions are expressed as δ values relative to V-PDB for both carbon and oxygen (in ‰ δ units). The oxygen values were converted from V-PDB to V-SMOW following the equation from [START_REF] Coplen | Comparison of stable isotope reference samples[END_REF].

Robustness of the stable isotope record

In contrast to the structure of extant mammal teeth, tooth enamel of Permian tetrapods is so thin that it was not possible to sample enough material suitable for isotopic analysis.

Consequently, we focused our sampling on bone and tooth dentine; however, those bioapatites have more porous apatite than enamel, with smaller and less densely inter-grown crystals [START_REF] Mills | Structural and Chemical Organization of Teeth[END_REF]. Thus, secondary precipitation within or on the surface of bioapatite crystals, adsorption of ions on the surface of those crystals, or even dissolution and recrystallization along with isotopic exchange could have altered their original isotope composition. To differentiate apatites "isotopically-altered" by diagenesis from those partly altered or unaltered, all samples were tested for primary preservation by comparing their δ 18 O p values against their δ 18 O c values as recommended by [START_REF] Iacumin | Oxygen isotope analyses of coexisting carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate?[END_REF].

In the skeletal tissue of extant mammals, the δ 18 O p and δ 18 O c are positively correlated because apatite precipitates close to equilibrium with water for both phosphate and carbonate components. As isotopic exchange rates between carbonate-water and phosphate-water are highly contrasted, re-equilibration of both compounds during diagenesis is not expected to be a common process and altered enamel should show isotopic shifts from the empirical δ 18 O pδ 18 O c line [START_REF] Iacumin | Oxygen isotope analyses of coexisting carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate?[END_REF]. It is therefore expected that the distribution of pristine or weakly altered δ 18 O p and δ 18 O c values should display a positive regression line with a slope close to unity. At low temperature, inorganic alteration has little effect on the phosphate of the apatite, even at the scale of geological time [START_REF] Tudge | A method of analysis of oxygen isotopes in orthophosphate-its use in the measurement of paleotemperatures[END_REF][START_REF] Lécuyer | Oxygen isotope exchange between dissolved phosphate and water at temperatures ≤135°C: inorganic versus biological fractionations[END_REF], and would result in high overall carbonate content or a low discrepancies between carbonate δ 18 O c and phosphate δ 18 O p values. However, apatites can be mineralogically and isotopically altered during microbially-mediated diagenesis [START_REF] Zazzo | Experimentally-controlled carbon and oxygen isotope exchange between bioapatites and water under inorganic and microbiallymediated conditions[END_REF], which should be shown by greater δ 18 O c -δ 18 O p differences. The carbonate content can be estimated from the mean magnitude of the current voltage (mV) measured during the analysis of the CO 2 by mass spectrometer (Supplementary Table 1).

Results

In our dataset, most of the samples analysed by mass spectrometry yielded peaks for the mass 44 with a mean magnitude of around 1000 mV and 3000 mV, which is in accordance with the sample weights [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF]. However, two samples (1782-B and 7241-B) are characterized by mean magnitudes of 3900 mV and 5600 mV respectively, which are greater than the rest of the studied sample, hence suggesting an excess of carbonate in the apatite structure. Moreover, δ 18 O p and δ 18 O c values of these samples significantly deviate from the empirical regression line (Fig. 3). Therefore, we consider that those two samples lost their pristine isotopic compositions. The altered state of the sample 1782-B was also highlighted by comparing bone and tooth isotopic ratios from the same specimens. While both δ 13 C c and δ 18 O p values (Fig. 4A-C) are close to the empirical line, the δ 18 O c value of bone sample 1782-B (Fig. 4B) is abnormally high compared to the tooth. Of the total of 43 samples, two are considered to have diagenetically altered δ 18 O c and δ 13 C c values.

Once the diagenetic and outlying values were removed from the dataset, the δ 18 O p and δ 18 O c values of the remaining weakly or non-altered samples were identified to range between 4.1‰ and 7.7‰ V-SMOW, and between 10.7‰ and 15.1‰ V-SMOW, respectively. Nonaltered samples have δ 13 C c values that range from -13.4‰ to -6.4‰ V-PDB. These results

show that the different species of pareiasaurs from neighbouring localities share similar δ 18 O p values. Consequently, for the purposes of this study we have not differentiated between the different pareiasaur genera.

Oxygen isotopes

For both the Moordenaars and Karelskraal Members, the δ 18 O p median values do not show significant differences compared to other δ 18 O p median values from the same horizon (Wilcoxon test p-values > 0.18; Fig. 5). This pattern most probably results from the difficulty in obtaining sufficiently large sample sizes for specimens of the same taxon from the same locality. Although no significant differences are apparent, it is noteworthy that pareiasaurs and titanosuchids have the highest mean oxygen isotope ratios for both horizons, with respectively 6.8‰ and 6.7‰ for the Karelskraal Member and 6.3‰ both for the Moordenaars Member.

For the Upper Leeuvlei Member, only one specimen of each species was available for sampling, thus precluding any comparison between taxon median oxygen isotope values. The rhinesuchid amphibian has the lowest δ 18 O value and the therocephalian Glanosuchus has the highest, while the dinocephalian Anteosaurus lies in between.

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Carbon isotopes

Similar to the oxygen values, the δ 13 C c median values are not significantly different from each other (Wilcoxon test p-values > 0.06). This outcome could result from the small sample size, but we note that the highest value documented in the Karelskraal Member corresponds to a titanosuchid, whilst the lowest one corresponds to a specimen of the therocephalian Glanosuchus; the opposite pattern was found for the lower-middle Moordenaars Member (Fig. 6). Pareiasaurs and dinocephalians have a consistent relationship throughout all horizons, with the pareiasaurs having higher median values than all dinocephalians. The Leeuvlei Member is characterized by almost identical values for the rhinesuchid amphibian and Glanosuchus while Anteosaurus is represented by a δ 18 O value 1‰ higher.

Discussion

Among all the sampled taxa, only one rhinesuchid temnospondyl individual represents the aquatic ecology. Indeed, the hypotheses for rhinesuchids being aquatic predators [START_REF] Schoch | Handbuch der Palaoherpetologie: 3B Stereospondyli[END_REF] has been strongly supported by bone microstructure analysis [START_REF] Mchugh | Paleohistology and histovariability of the Permian stereospondyl Rhinesuchus[END_REF]. Accordingly, a lower stable isotope oxygen value for the rhinesuchid relative to those for all the rest of the terrestrial taxa is expected from this individual (Fig. 5). The value difference between the rhinesuchid and Anteosaurus (0.79±0.68‰), or even Glanosuchus (1.46±0.92‰) (Fig. 5; Supplementary Table 1), is lower than those observed between semiaquatic and terrestrial extant mammal species (around 3‰ to 7‰; [START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF], but within the range observed for extinct reptiles. Indeed, a study on the aquatic ecology of spinosaurids [START_REF] Amiot | Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods[END_REF] showed differences of less than 2‰ between terrestrial theropods and aquatic crocodilians and turtles.

Was Anteosaurus a fully terrestrial therapsid?

The arguments given by Ivakhnenko (2008, p. 969) in favour of an amphibious lifestyle for Anteosaurus was that it possessed a "high skull with considerably elevated nares and orbits, and thin, gracile skeleton with wide manus and poorly ossified epiphysial regions of tubular bones […] and the postcranial skeleton corresponds to the aquatic mode of life".

The arguments in favour of a terrestrial lifestyle has also made reference to morphology (Kammerer, 2011, pp. 295-296): "Aquatic and semiaquatic piscivores generally have a relatively small cranium (excluding the jaws), as a heavy skull would reduce acceleration during pursuit of evasive prey [START_REF] Taylor | Functional anatomy of the head of the large aquatic predator Rhomaleosaurus zetlandicus (Plesiosauria, Reptilia) from the Toarcian (Lower Jurassic) of Yorkshire, England[END_REF] […], the non-jaw region of the skull is massive, extremely so in the giant taxa Titanophoneus and Anteosaurus. The postcranial anatomy of anteosaurids is also not suggestive of amphibious habits.

[…] anteosaurids have relatively elongate limbs for dinocephalians (Boonstra, 1955)."

Considerations of taphonomy have tended towards the same conclusion "anteosaur fossils are usually found in deltaic facies [START_REF] Olson | Late Permian terrestrial vertebrates, USA and USSR[END_REF][START_REF] Rubidge | Biostratigraphy of the Beaufort Group (Karoo Supergroup), Biostratigraphic Series[END_REF], taphonomic evidence suggests that, at least for the South African taxa, these remains were washed in from upland habitats (Boonstra, 1969;[START_REF] Kitching | The distribution of the Karroo vertebrate fauna: with special reference to certain genera and the bearing of this distribution on the zoning of the Beaufort beds[END_REF]." (Kammerer, 2011, p. 296).

In the Karelskraal Member, Anteosaurus has the lowest δ 18 O p value (Fig. 5), which could indicate that this therapsid had a closer relationship to water than did the other sampled therapsids [START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF][START_REF] Amiot | Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods[END_REF]. This observation is consistent with the data from the upper Leeuvlei Member, where the δ 18 O p value obtained for Anteosaurus is intermediate between that of the therapsid Glanosuchus and the rhinesuchid temnospondyl.

However, this pattern may be the result of a small sample size because δ 18 O p values for Anteosaurus sampled from the lower-middle Moordenaars Member have a similar range to those measured in other sampled tetrapod taxa from this stratigraphic interval for which larger sample sizes are available (n≥4), i.e. pareiasaurs and titanosuchids (Fig. 5). The range of δ 18 O p values for Anteosaurus also overlaps values obtained for the tapinocephalid Criocephalosaurus (n=2) and Glanosuchus (n=1) and even includes the highest recorded value for δ 18 O (7.5‰). Therefore, while the value from the Leeuvlei Member belongs to the same range of values from the Moordenaars Member, the very low value from the Karelskraal Member might need more careful consideration as it may not be reflective of the lifestyle of the species.

Distinguishing between a riparian or other terrestrial lifestyles for dinocephalians cannot be tested with stable oxygen isotopes. Extant riparian mammal species, such as the waterbuck Kobus ellipsiprymnus [START_REF] Pacini | 6 -Aquatic, Semi-Aquatic and Riparian Vertebrates[END_REF], show values similar to those of other terrestrial species [START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF]. The "stable isotope tracer" is sensitive to water dependency and not to the habitat of the species. Therefore, based on the few sampled Anteosaurus from the Karoo Basin, our isotopic results tend to favour the terrestrial hypotheses, but cannot determine if the species was riparian or an in-land dweller.

Were middle Permian South African pareiasaurs aquatic or terrestrial?

Previous published suggestions for a semi-aquatic lifestyle in pareiasaurs are even more subjective. "The mode of life of pareiasaurs was similar to that of the hippopotamus: they spent most of the time in water, occasionally coming out" (Khlyupin, 2007, p. 3) or " [START_REF] Ivakhnenko | Tetrapods from the east european placket-Late Paleozoic natural territorial complex[END_REF] believes that details of the skeleton structure of Scutosaurus point to its aquatic mode of life and its poor terrestrial locomotion" (Gubin et al., 2003, p. 522). [START_REF] Kriloff | Evolution of bone microanatomy of the tetrapod tibia and its use in palaeobiological inference[END_REF] interpreted Pareiasaurus as an aquatic animal, based on their models from bone microanatomy, but changed to semi-aquatic on the basis of morphological characters such as "its morphology (i.e. its well-ossified skeleton, and possibly graviportal adaptations) suggests adequate terrestrial locomotor abilities, and this taxon will be considered as amphibious (rather than aquatic) for the optimizations" (Kriloff et al., 2008, p. 817). Their argument continues further with "The bones of the pareiasaur Bunostegos have been described as spongy and pachyostotic (Sidor et al., 2003, p. 46), which is also compatible with an amphibious or aquatic habitat" (Kriloff et al., 2008, p. 817).

The terrestrial hypothesis is supported by ichnofossils ascribed to pareiasaurs [START_REF] Gubin | Pareiasaurian tracks from the upper Permian of Eastern Europe[END_REF][START_REF] Valentini | A re-evaluation of Pachypes, a pareiasaurian track from the Late Permian[END_REF][START_REF] Voigt | Tetrapod footprints from the uppermost level of the Permian Ikakern Formation (Argana Basin, Western High Atlas, Morocco)[END_REF]. Other publications support the purported terrestrial lifestyle of pareiasaurs based on limb morphology such as "the numerous postcranial autapomorphies of Bunostegos suggest a suite of derived features related to a relatively parasagittal (i.e., nonsprawling) forelimb posture" (Turner et al., 2015, p. 12).

Earlier carbonate stable oxygen isotope analysis also suggests that "pareiasaurs were terrestrial browsers and are inconsistent with the earlier semiaquatic ecomorph hypothesis proposed" (Canoville et al., 2014, p. 7).

Teeth and bones of middle Permian pareiasaurs, which were sampled from both the Moordenaars and the Karelskraal Members of the Abrahamskraal Formation, have similar δ 18 O p values. The range of these values, approximately 2‰, is similar to that of extant mammal species ranging from 2‰ (lion, waterbuck) to 5‰ (rhino, buffalo) [START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF], a bracket which includes all values obtained for the taxa in our sample. The absence of a significant difference between the median values of the different groups (Wilcoxon test pvalues > 0.18; Fig. 5) indicate that dinocephalians, therocephalians, and the pareiasaurs could have shared a similar terrestrial lifestyle.

This study of the lifestyle of pareiasaurs through a geochemical proxy, the δ 18 O p values from the phosphate group of the apatite, is in alignment with previously published studies that interpreted pareiasaurs as a fully terrestrial taxon. It is important to stress that this study focused only on middle Permian pareiasaurs from the Karoo Basin of South Africa, which are the oldest pareiasaurs known ( [START_REF] Van Den Brandt | Cranial morphology and phylogenetic relationships of the Middle Permian pareiasaur Embrithosaurus schwarzi from the Karoo Basin of South Africa[END_REF], and that different results might be obtained from analyses of later species.

Conclusions

Stable oxygen and carbon isotope compositions of phosphate apatite of teeth and bones were analyzed to investigate the debated ecological lifestyle of middle Permian pareiasaurs and the dinocephalian Anteosaurus. Our results demonstrate that the aquatic ecology of the rhinesuchid specimen is strongly supported by its low δ 18 O p value, the lowest of the horizon. For Anteosaurus, our results favour the terrestrial hypotheses, but a single low

Figure captions

Figure 1: Mean oxygen isotope compositions of apatites versus drinking waters of mammals from two Kenyan parks [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF][START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF] showing difference in Table 1: Mean oxygen isotope compositions of apatites of mammals from two Kenyan parks [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF][START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF]. V-PDB: Vienna PeeDee Belemnite; V-SMOW:

Vienna standard mean ocean water. Equations from [START_REF] Coplen | Comparison of stable isotope reference samples[END_REF] and [START_REF] Lécuyer | Oxygen isotope fractionation between apatite-bound carbonate and water determined from controlled experiments with synthetic apatites precipitated at 10-37 °C[END_REF] [START_REF] Coplen | Comparison of stable isotope reference samples[END_REF] was used to convert δ18Oc (V-PDB) values into δ18Oc (V-SMOW) values. Equations from [START_REF] Lécuyer | Oxygen isotope fractionation between apatite-bound carbonate and water determined from controlled experiments with synthetic apatites precipitated at 10-37 °C[END_REF] was used to convert δ18Oc (V-SMOW) values into δ18Op (V-SMOW) values. SD correspond to ±1σ.

Highlights:

-First application of δ 18 O p of apatite to South African tetrapods for paleoecology.

-The lifestyle of middle Permian pareiasaurs is strongly shown to be terrestrial.

-The carnivorous dinocephalian Anteosaurus was probably living a terrestrial ecology.

-Knowing the ecology of major species helps understand the nature of the extinction.

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  for measuring the oxygen isotope composition of the apatite carbonate. Powders were washed with a 2% NaOCl solution to remove organic matter, then rinsed five times with double deionized water and air-dried at 40 °C for 24 hours. Potential secondary carbonate was removed by adding 0.1 M acetic acid and leaving overnight, after which the powder was again rinsed five times with double deionized water and air-dried at 40 °C overnight. The powder/solution ratio was kept constant at 0.04 g.mL -1 for both treatments. The tubes were placed in a Thermo Finnigan Model II gas bench in a temperature controlled sampler tray set to 72°C (housed in the Stable Light Isotope Laboratory of the Archaeology Department of the University of Cape Town). For each sample, an aliquot of 2 mg of pre-treated apatite was Journal Pre-proof J o u r n a l P r e -p r o o f 10 reacted with 7 drops of supersaturated orthophosphoric acid at 72 °C for at least two hours under a He atmosphere before starting 9 measurement cycles of the isotopic composition of the CO 2 produced with a Thermo Finnigan Delta Plus XP continuous flow isotope ratio mass spectrometer. The measured carbon and oxygen isotopic compositions were calibrated relative to the NBS-18, NBS-19 and an internal calcite standard 'Cavendish Marble'. Reproducibility

  δ 18 O p value questions the robustness of this interpretation. A future isotope study focusing on the ecology of Anteosaurus with an increased sample size may result in a more conclusive outcome. The middle Permian pareiasaurs, on the other hand, are represented by values all indicating a terrestrial way of life, which support the outcomes of previous taphonomic and geochemical studies. acknowledged for access to the Karoo fossil collections of the ESI and for sanction to sample the tetrapod fossils. This work was supported by the Palaeontological Scientific Trust (PAST) and its Scatterlings of Africa programmes, National Research Foundation (NRF) African Origins Platform of South Africa (grant no. 98802) and DST/NRF Centre of Excellence in Palaeosciences.

  δ18 O p values between semiaquatic hippopotamuses and terrestrial herbivorous mammals (error bars are ±1σ). V-SMOW-Vienna standard mean ocean water. Phosphate-water fractionation lines of terrestrial placental mammals, freshwater turtles, and crocodilians are displayed for comparison. Equations from[START_REF] Coplen | Comparison of stable isotope reference samples[END_REF] and[START_REF] Lécuyer | Oxygen isotope fractionation between apatite-bound carbonate and water determined from controlled experiments with synthetic apatites precipitated at 10-37 °C[END_REF] were used to respectively convert δ 18 O c (V-PDB) values from[START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF] into δ 18 O c (V-SMOW) values and δ 18 O c (V-SMOW) values from[START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF] and[START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF] to δ 18 O p (V-SMOW) values. Updated from[START_REF] Amiot | Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods[END_REF].

Figure 2 :

 2 Figure 2: Studied localities along with the main lithostratigraphic units of the western part of

Figure 3 :

 3 Figure 3: Phosphate δ 18 O p values plotted against corresponding carbonate δ 18 O c values,

Figure 4 :

 4 Figure 4: Bone values ( b ) are plotted against tooth values ( t ) of the same individual and compared to a line with a slope of 1, for their δ 18 O p values (A), δ 18 O c values (B) and δ 13 C c

Figure 5 :

 5 Figure 5: Box plot of apatite δ 18 O p values of each taxon plotted within their respective

Figure 6 :

 6 Figure 6: Box plot of apatite δ 13 C c values of each taxon plotted within their respective

  were used to respectively convert δ 18 O c (V-PDB) values into δ 18 O c (V-SMOW) values and δ 18 O c (V-SMOW) values into δ 18 O p (V-SMOW) values. SD correspond to ±1σ.

Figure 2 Figure 3

 23 Figure2

Figure 4

 4 Figure4

Figure 5

 5 Figure5

Figure 6

 6 Figure6

Table 1 .

 1 Mean oxygen isotope compositions of apatites of mammals from two Kenyan parks

	Common name	Species name	Tsavo National Park	Ambolesi Park
			δ 18 O c δ 18 O p SD	δ 18 O c δ 18 O c δ 18 O p SD
				(‰, V-		(‰, V-PDB)	(‰, V-
				SMOW)			SMOW)
	Terrestrial species
	Buffalo	Syncerus caffer	30.9	21.8 1.4	1.7	32.7	23.5 0.9
	Elephant	Loxodonta africana	29.8	20.7 0.9	0.5	31.4	22.3 0.6
	Giraffe	Giraffa camelopardalis				4.3	35.3	26.1 0.8
	Lion	Panthera leo				0.7	31.6	22.5 0.5
	Oryx	Oryx beisa				2.4	33.4	24.2 1.7
	Rhinoceros	Diceros bicornis	29.5	20.4 1.3	0.7	31.6	22.5 1.4
	Warthog	Phacochoerus aethiopicus	31.0	21.9	-
	Waterbuck	Kobus ellipsiprymnus				2.4	33.4	24.2 0.9
	Wildebeest	Connochaetes taurinus	33.4	24.2 0.9
	Zebra	Equus burchelli	31.4	22.3 1.5	3.2	34.2	25.0 1.6
	Semi-aquatic species
	Hippopotamus	Hippopotamus amphibius	26.9	17.9 1.6	-2.7	28.1	19.1 0.8
	V-PDB: Vienna PeeDee Belemnite.
	V-SMOW: Vienna standard mean ocean water.
	Equations from

Acknowledgments

The authors thank the South African Heritage Resources Agency (SAHRA) for their authorization to sample the fossils, and export sub-samples for stable isotope analysis of phosphate (PermitID: 2541). Marion Bamford, Bernhard Zipfel and Sifelani Jirah are Journal Pre-proof J o u r n a l P r e -p r o o f

Scutosaurus karpinskii) with implications for pareiasaurian palaeobiology. Biol J Linn Soc 1-22. https://doi.org/10.1093/biolinnean/blz094 Bond, D.P.G., Wignall, P.B., 2014. Large igneous provinces and mass extinctions: an update. Geological Society of America Special Papers 505, SPE505-02.

Bond, D.P.G., Wignall, P.B., Wang, W., Izon, G., Jiang, H., Lai, X., Sun, Y., Newton, R.J., Shao, L.-Y., Védrine, S., others, 2010. The mid-Capitanian (Middle Permian) mass extinction and carbon isotope record of South China. Palaeogeography, Palaeoclimatology, Palaeoecology 292, 282-294. Boonstra, L.D., 1969. The fauna of the Tapinocephalus zone (Beaufort beds of the Karoo). Annals of The South African Museum 56, 1-73. Boonstra, L.D., 1962. The dentition of the titanosuchian dinocephalians. Annals of The South African Museum 46, 57-112. Boonstra, L.D., 1955. The girdles and limbs of the South African Deinocephalia. Annals of The South African Museum 42, 185-326. Bryant, J.D., Froelich, P.N., 1995. A model of oxygen isotope fractionation in body water of large mammals. Geochimica et Cosmochimica Acta 59, 4523-4537. https://doi.org/10.1016/0016-7037(95)00250-4 Canoville, A., Chinsamy, A., 2017. Bone Microstructure of Pareiasaurs (Parareptilia) from the Karoo Basin, South Africa: Implications for Growth Strategies and Lifestyle Habits. The Anatomical Record 300, 1039-1066. Canoville, A., Chinsamy, A., 2015. Bone microstructure of the stereospondyl Lydekkerina huxleyi reveals adaptive strategies to the harsh post Permian-extinction environment. The Anatomical Record 298, 1237-1254. https://doi.org/10.1002/ar.23160 Journal Pre-proof

J o u r n a l P r e -p r o o f

Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:


Kévin Rey
email: kevin.rey@wits.ac.za

Michael O Day
email: michael.day@nhm.ac.uk

Romain Amiot
email: romain.amiot@univ-lyon1.fr

François Fourel

Julie Luyt
email: julie.luyt@uct.ac.za

Christophe Lécuyer
email: christophe.lecuyer@univ-lyon1.fr

Bruce S Rubidge
email: bruce.rubidge@wits.ac.za.

Stable isotopes

Keywords: PALAEO late Permian, stable isotopes, Poortjie Member, Hoedemaker Member, herbivory, insectivory

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Dicynodonts were a highly successful clade of therapsids that formed a major part of the herbivore guild in tetrapod communities from the mid-Permian to the mid-Triassic. One reason for their success was likely their development of keratinous sheaths on the palate and lower jaw, combined with greatly expanded adductor jaw musculature [START_REF] Kemp | The origin and radiation of Therapsids[END_REF]. All dicynodonts possess a keratinous beak in lieu of precanine teeth but in more derived forms the post-canine teeth are entirely lost, though most retain a pair of canine tusks. Of the earliestdiverging taxa, Endothiodon is peculiar in that it is characterized by relatively long upper and lower tooth rows on the dentary, premaxilla and maxilla [START_REF] Ray | Endothiodont dicynodonts from the Late Permian Kundaram Formation, India[END_REF]. Teeth were replaced in waves in the dentary resulting in the appearance of multiple tooth rows (Macungo et al., J o u r n a l P r e -p r o o f Journal Pre-proof 2020). In adult individuals, the teeth are pear-shaped, posterolaterally compressed, and serrated, whereas in juveniles, they are small and conical [START_REF] Ray | Endothiodont dicynodonts from the Late Permian Kundaram Formation, India[END_REF].

This peculiar tooth pattern and other unique features of the skull and jaw have raised questions about the feeding biomechanics of Endothiodon, most recently discussed by [START_REF] Cox | A new endothiodont dicynodont (Therapsida, Anomodontia) from the Permian Ruhuhu Formation (Songea Group) of Tanzania and its feeding system[END_REF]. A corollary question to this that remains poorly understood is to which diet was this specialized feeding apparatus adapted. [START_REF] Cox | On the palate, dentition, and classification of the fossil reptile Endothiodon and related genera[END_REF] suggested that Endothiodon used its beak to grub vegetable matter out of the ground, such as roots and tubers, whereas [START_REF] Latimer | Dentition and feeding niche of Endothiodon (Synapsida; Anomodontia[END_REF] postulated that Endothiodon was a specialised browser that subsisted on dense riparian vegetation. [START_REF] Cox | The jaw function and adaptive radiation of the dicynodont mammal-like reptiles of the Karoo basin of South Africa[END_REF] proposed an even more specialised feeding niche based on the unusual vaulted palate, interpreting it as an adaptation to processing conifer cones to extract the seeds. The difference between juvenile and adult teeth has also been taken to reflect a change of diet during ontogeny [START_REF] Parks | Cranial anatomy and mastication of the Triassic reptile Trilophosaurus[END_REF]cf. Demar and Bolt, 1981), whereby juveniles subsisted on a more generalised diet comprising vegetation and possibly invertebrates that transitioned into more specialized herbivory in adults [START_REF] Ray | Endothiodont dicynodonts from the Late Permian Kundaram Formation, India[END_REF]. The specialized feeding system and diet of Endothiodon are of particular interest because in Gondwanan basins for which biostratigraphic resolution is sufficiently good, this taxon appears to be the first large herbivore to appear after the extinction of dinocephalian therapsids [START_REF] Angielczyk | Permian and Triassic dicynodont (Therapsida: Anomodontia) faunas of the Luangwa Basin, Zambia: taxonomic update and implications for dicynodont biogeography and biostratigraphy[END_REF]Day et al., 2015b;Day and Smith, in press). In the southwestern part of the Main Karoo Basin of South Africa, this extinction occurs at or slightly above the base of the Poortjie Member of the Teekloof Formation (Day et al., 2015a[START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF].

Endothiodon has its lowest occurrence in the mid-Poortjie Member (Pristerognathus Assemblage Zone=lower Endothiodon Assemblage Zone), and ranges up into the overlying The disappearance of dinocephalians has been linked to the Capitanian mass extinction (Day et al., 2015b;[START_REF] Schneider | Late Paleozoic-early Mesozoic continental biostratigraphy -Links to the Standard Global Chronostratigraphic Scale[END_REF] and Endothiodon is thus an important part of the tetrapod recovery, having its greatest relative abundance soon after its initial appearance (Day and Smith in press). As noted by [START_REF] Cox | A new endothiodont dicynodont (Therapsida, Anomodontia) from the Permian Ruhuhu Formation (Songea Group) of Tanzania and its feeding system[END_REF]p. 22),'if Endothiodon was a dietary specialist, its broad geographic distribution indicates that its preferred food source must have been widespread', which suggests that the foodstuffs were especially common after extinction event, or were more resilient to any environmental changes that had contributed to it. The palaeobotanical record for the tetrapod-bearing sequences at this time is, however, very poor. Nevertheless, a better understanding of the diet and lifestyle (i.e. water dependence) of Endothiodon could provide useful information about the environmental and floral changes associated with the early recovery of terrestrial ecosystems after the Capitanian mass extinction.

Stable carbon and oxygen isotope studies of bone and tooth apatite offer the possibility to better identify both the diet and the lifestyle of vertebrates. Indeed, the δ 18 O value of apatite is correlated to both body temperature and to the oxygen isotope composition of vertebrate body water (δ 18 Obw) which is mostly derived from the consumption of either meteoric water or plant water, or a combination of both [START_REF] D'angela | Evolutionary rates of mid-Permian tetrapods from South Africa and the role of temporal resolution in turnover reconstruction[END_REF][START_REF] Kohn | Predicting animal δ 18 O: Accounting for diet and physiological adaptation[END_REF]. Water oxygen input and output between the environment and the animal's body differ between terrestrial and aquatic species. This is expressed by a difference of magnitude of 18 Oenrichment of body water relative to drinking water, caused mostly by transcutaneous evaporation, urine or faeces [START_REF] Luz | Oxygen isotope variations in phosphate of biogenic apatites, IV. Mammal teeth and bones[END_REF][START_REF] Bryant | A model of oxygen isotope fractionation in body water of large mammals[END_REF]Amiot et al., J o u r n a l P r e -p r o o f Journal Pre-proof 2007,2010). Extant mammals consuming large quantities of water, or spending time in it have lower δ 18 Obw values than those with a terrestrial ecology [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF][START_REF] Kohn | Herbivore tooth oxygen isotope compositions: Effects of diet and physiology[END_REF][START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF]. For instance, the δ 18 O value recorded in apatite of hippopotamuses is lower than that of other terrestrial mammals. Depending on the waterdependence of the terrestrial species, δ 18 O values of hippopotamus are about 3‰ lower than those of water-dependent animals and the difference can be as high as 7‰ when compared with water-independent species [START_REF] Bocherens | Isotopic biogeochemistry (δ 13 C, δ 18 O) of mammalian enamel from African Pleistocene hominid sites[END_REF][START_REF] Cerling | Stable isotope ecology of the common hippopotamus[END_REF][START_REF] Clementz | Identifying Aquatic Habits Of Herbivorous Mammals Through Stable Isotope Analysis[END_REF]. Therefore, by comparing the apatite δ 18 O values of various co-existing vertebrates with different lifestyles, it should be possible to interpret the ecology of extinct taxa.

Stable carbon isotope composition (δ 13 C) of vertebrate apatite can be used to estimate the diet of a species. Apatite-diet 13 C-enrichment varies between species, most probably as a result of different digestive patterns [START_REF] Deniro | Influence of diet on the distribution of carbon isotopes in animals[END_REF][START_REF] Quade | A 16-Ma record of paleodiet using carbon and oxygen isotopes in fossil teeth from Pakistan[END_REF][START_REF] Passey | Carbon isotope fractionation between diet, breath CO2, and bioapatite in different mammals[END_REF]. The apatite δ 13 C values of herbivorous animals reflect those of their vegetarian diet, and those of carnivorous animals originate from the flesh of their prey. The flesh-plant 13 C-enrichment in herbivore tissue is about 1 ± 1‰ [START_REF] Barnes | Effect of temperature and ration size on carbon and nitrogen stable isotope trophic fractionation[END_REF], whereas the plant δ 13 C value is controlled by its photosynthetic pathway [START_REF] Ehleringer | Evolutionary and ecological aspects of photosynthetic pathway variation[END_REF] and environmental conditions [START_REF] Kohn | Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate[END_REF]. During the Permo-Triassic, plants used only the C3 pathway [START_REF] Osborne | Nature's green revolution: the remarkable evolutionary rise of C4 plants[END_REF], and today C3 plants record δ 13 C values between -35‰ and -22‰ [START_REF] Smith | Two Categories of 13 C/ 12 C Ratios for Higher Plants 1[END_REF][START_REF] O'leary | Carbon isotope fractionation in plants[END_REF]. This range of values results from the different environments in which the plants grow. An increase in openness of the environment, water-stress or sunlight will increase δ 13 C values of the plants (reviewed in [START_REF] Ehleringer | Evolutionary and ecological aspects of photosynthetic pathway variation[END_REF]. As a result, the difference of δ 13 C values between species could indicate a difference in diet and lifestyle. To determine whether Endothiodon had a different ecology and diet to that of the other dicynodonts, we compare stable oxygen (δ 18 Op J o u r n a l P r e -p r o o f Journal Pre-proof and δ 18 Oc) and carbon (δ 13 Cc) isotope compositions of bone and teeth from specimens of Endothiodon with values from specimens of Tropidostoma from the same localities, although Tropidostoma first appears only in the Hoedemaker Member. These results are also compared to published values for Diictodon [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF] from the same stratigraphic interval to distinguish differences between ecological and environmental factors.

Material and methods

Sample Collection

The bones of sixteen tetrapod fossils were sampled, of which three also had their teeth sampled. All samples were analysed for their stable oxygen and carbon isotope composition of apatite phosphate and carbonate. Sample sizes were limited by the availability of particular species from specific geological horizons and the presence of suitable specimens with appropriate stratigraphic and reliable taxonomic data bearing in mind the destructive nature of sampling for stable isotope analysis. The samples collected for this study included six Endothiodon sp., nine Tropidostoma sp., and one unidentified pareiasaur. These fossils were recovered from three localities in the Main Karoo Basin of South Africa which all cover the same stratigraphic interval and are geographically separated by less than a hundred kilometres, between 21.25° and 22.08° of latitude and -32.31 and -32.22° of longitude (Fig. 1; Supplementary Table 1). The lithostratigraphy at each of these localities is well defined and all sampled fossils can be stratigraphically positioned with a high degree of precision between the Poortjie Member and the Lower Hoedemaker Member. All specimens are curated at the Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg.

Analytical techniques

J o u r n a l P r e -p r o o f

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We isolated the phosphate ions using acid dissolution and anion-exchange resin in order to measure the oxygen isotope composition of the apatite phosphate group [START_REF] Lécuyer | Oxygen isotope analysis of phosphate[END_REF]. Once quantitatively precipitated in a thermostatic bath set at a temperature of 70 °C, the silver phosphate was filtered, washed with double deionized water, and dried at 50 °C.

Oxygen isotope compositions of the Ag3PO4 crystals were measured using a high-temperature pyrolysis technique involving a VarioPYROcube TM elemental analyzer (EA) interfaced in continuous flow (CF) mode to an Isoprime TM isotopic ratio mass spectrometer (IRMS) (EA-Py-CF-IRMS technique) at the Laboratoire de Géologie de Lyon (UMR 5276, Université Claude Bernard Lyon 1). For each sample, 5 aliquots of 300 μg of Ag3PO4 were mixed with 300 μg of pure graphite powder and loaded in silver foil capsules. Pyrolysis was performed at 1450 °C. Measurements were calibrated against the NBS120c (natural Miocene phosphorite from Florida: δ 18 O = 21.7‰; [START_REF] Lécuyer | Thermal excursions in the ocean at the Cretaceous-Tertiary boundary (northern Morocco): δ 18 O record of phosphatic fish debris[END_REF]) and the NBS127 (barium sulfate, BaSO4: δ 18 O = 9.3‰; [START_REF] Hut | Consultants' group meeting on stable isotope reference samples for geochemical and hydrological investigations[END_REF]. Silver phosphate samples precipitated from standard NBS120c were repeatedly analysed (δ 18 Op = 21.7‰; 1σ = 0.3; n = 8) along with the silver phosphate samples derived from fossil bioapatites to ensure that no isotopic fractionation occurred during the wet chemistry. Data are reported as δ 18 Op values vs. V-SMOW in ‰ δ units.

To measure the oxygen isotope composition of the apatite carbonate group, about 10 mg of tooth or bone powder was pre-treated [START_REF] Koch | The effects of sample treatment and diagenesis on the isotopic integrity of carbonate in biogenic hydroxylapatite[END_REF]. Powders were washed with a 2% NaOCl solution to remove organic matter and were then rinsed five times with double deionized water and air-dried at 40 °C for 24 hours. Potential secondary carbonate was removed by adding 0.1 M acetic acid to the powder and leaving overnight, after which the powder was rinsed five times with double deionized water and air-dried at 40 °C overnight.

The powder/solution ratio was kept constant at 0.04 g mL -1 for both treatments. Stable isotope ratios were determined using a Thermo Gasbench II at the Stable Light Isotope Laboratory of

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Journal Pre-proof the Archaeology Department of the University of Cape Town. For each sample, an aliquot of 2 mg of pre-treated apatite was reacted with 7 drops of supersaturated orthophosphoric acid at 72 °C for at least two hours under a He atmosphere before starting 9 measurement cycles of the isotopic composition of the CO2 produced with a Thermo Finnigan Delta Plus XP continuous flow isotope ratio mass spectrometer. The measured carbon and oxygen isotopic compositions were normalized relative to the NBS-18, NBS-19 and an internal calcite standard 'Cavendish Marble' (δ 13 C = 0.34‰; δ 18 O = -8.95‰). Reproducibility for the carbon and oxygen isotopic compositions of apatite carbonate is better than ±0.10‰ and ±0.15‰, respectively. The carbon and oxygen isotopic compositions are expressed as δ values relative to V-PDB for both carbon and oxygen (in ‰ δ units). The oxygen values were converted from V-PDB to V-SMOW following the equation from [START_REF] Coplen | Comparison of stable isotope reference samples[END_REF].

Robustness of the stable isotope record

The enamel layer of Permian tetrapod teeth is so thin that only dentine and bones could be sampled for analysis. Both have more porous apatite than enamel, with smaller and less densely inter-grown crystals [START_REF] Mills | Structural and Chemical Organization of Teeth[END_REF]. As a result, secondary precipitation within or at the surface of the bioapatite crystals, adsorption of ions on the surface of those crystals, or even the dissolution and recrystallization with isotopic exchange might have altered their original isotope compositions. To differentiate apatite altered by diagenesis, all samples were tested for primary preservation by comparing their δ 18 Op values against their δ 18 Oc values.

In skeletal tissues of extant mammals, the δ 18 Op and δ 18 Oc are positively correlated because of precipitation close to equilibrium with body water in both phosphate and carbonate. Re-equilibration of those compounds during diagenesis is not expected because J o u r n a l P r e -p r o o f Journal Pre-proof isotopic exchange rates between carbonate-water and phosphate-water are radically different.

Therefore altered enamel should show isotopic shifts from the empirical δ 18 Op-δ 18 Oc line [START_REF] Iacumin | Oxygen isotope analyses of coexisting carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate? Earth Planet[END_REF]Zazzo et al., 2004b). Accordingly, it is expected that the distribution of pristine δ 18 O values should display a positive regression line with a slope close to unity. Also, at low temperature, inorganic alteration has little effect on the phosphate of the apatite, even in geological time [START_REF] Tudge | A method of analysis of oxygen isotopes in orthophosphate-its use in the measurement of paleotemperatures[END_REF][START_REF] Lécuyer | Oxygen isotope exchange between dissolved phosphate and water at temperatures ≤135°C: inorganic versus biological fractionations[END_REF], but the phosphate can be altered by microbially mediated diagenesis (Zazzo et al., 2004a). The inorganic alteration would result in a high overall carbonate content or a low discrepancy between carbonate δ 18 Oc and phosphate δ 18 Op values, whereas organic alteration should show the opposite with a greater δ 18 Oc-δ 18 Op value. The carbonate content can be estimated from the mean magnitude of the current voltage (mV) measured during the analysis of the CO2 by mass spectrometer (Supplementary Table 1).

In our dataset, most of the analysed samples yielded peaks for the mass 44 ions with a mean amplitude ranging from around 1500 mV and 3100 mV, which is in accordance with the weight of the samples. However, four samples, 7267-B; 7570-B; 7618-B and 7624-B (with B standing for 'bone sample'), gave mean magnitudes greater than 3400 mV, even reaching more than 10000 mV, suggesting an excess of secondary precipitated carbonate in the apatite.

Accordingly, their δ 18 Oc and δ 13 C values have been considered to not represent the original signal and were discarded.

Among the four discarded specimens, one (7267-B) has a tooth which had also been sampled. Comparison of the δ 18 Oc values between teeth and bones of the same individuals (Fig. 2) shows that the values follow a slope close to unity except for sample 7267-B, confirming the altered status of the carbonate values for the bone sample of this individual.

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In addition, comparison between δ 18 Op and δ 18 Oc values (Fig. 3) shows that four specimens deviate from the theoretical line with a slope equal to one. Three of them (7267-B; 7570-B and 7618-B) have already been discarded for their δ 18 Oc and δ 13 C values, with even higher discrepancies between carbonate δ 18 Oc and phosphate δ 18 Op values, based on their elevated mean magnitude. The forth one, (7754-B), presents an expected mean magnitude of its signal, and therefore cannot be discarded based on its δ 18 Oc values but rather on δ 18 Op. One data point (7624-B) has a very high mean magnitude but does not fit with the other discarded values (Fig. 3). The possible reason is that its phosphate group has also been altered and thus the δ 18 Op value does not represent the original signal and should thus also be discarded.

Finally, one data point (7753-B), which has an outlying δ 13 C value compared to those of other samples of the same species and from the same stratigraphic horizon, had to be discarded for its carbon isotope value. In summary, two of the 19 values have been discarded due to their anomalous δ 18 Op, four for their δ 18 Oc, and five for their δ 13 C.

Results

The δ 18 Op and δ 18 Oc values of the sixteen non-altered samples range between 5.2‰ and 8.0‰ V-SMOW and between 11.2‰ and 16.6‰ V-SMOW, respectively. Non-altered samples have δ 13 Cc values ranging from -10.8‰ to -7.8‰ V-PDB. The δ 18 Op and the δ 13 Cc values are plotted against their stratigraphic position in Figures 4 and5.

Oxygen isotopes

The five Endothiodon specimens from the Poortjie Member have δ 18 Op values that range from 5.4 ± 0.1‰ to 6.2 ± 0.2‰ V-SMOW. An unidentified pareiasaur from the middle

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Journal Pre-proof of this member has a higher value of 8.0 ± 0.4‰ V-SMOW. The eight Tropidostoma specimens from the overlying Hoedemaker Member yielded δ 18 Op values that range from 6.1 ± 0.2‰ to 7.5 ± 0.1‰ V-SMOW. A Wilcoxon Mann-Whitney test reveals a significant difference between the median value of the Endothiodon and Tropidostoma sample populations (p-value = 0.003).

Carbon isotopes

For the carbon isotopes, we considered four Endothiodon specimens, the pareiasaur mentioned above, and seven of the Tropidostoma specimens to be unaltered. The Endothiodon δ 13 Cc values range from -10.8 ± 0.1‰ to -9.3 ± 0.1‰ V-PDB, the pareiasaur has a slightly higher value of -9.2 ± 0.1‰ V-PDB, and the Tropidostoma values range from -9.5 ± 0.1‰ to -7.8 ± 0.0‰ V-PDB. The median values for the Endothiodon and Tropidostoma sample populations also show significant differences when tested with a Wilcoxon Mann-Whitney (p-value = 0.017).

Discussion

Oxygen isotopes and the water dependence of Endothiodon

The significantly lower δ 18 Op values for Endothiodon relative to Tropidostoma (Fig. 4) suggest a difference of ecology; however, because the sampled specimens of each species come from different stratigraphic horizons there is the possibility that this reflects a difference in environmental isotopic values, which are variable over time. To account for this phenomenon we referred to a third dicynodont taxon, Diictodon feliceps, which at the Muggefontein locality has previously been sampled from both the Poortjie and Hoedemaker members [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF]Fig. 4). This study demonstrated that δ 18 Op values of Diictodon

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Journal Pre-proof were consistent between the Poortjie and Hoedemaker members and led [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF] to conclude that there was no temperature change between the Pristerognathus and Tropidostoma Assemblage Zone. Consequently, we take the difference in the range of oxygen isotope composition between Endothiodon and Tropidostoma to be the result of a difference in water dependence.

As is the case in most dicynodonts [START_REF] Nicolas | Changes in Permo-Triassic terrestrial tetrapod ecological representation in the Beaufort Group (Karoo Supergroup) of South Africa[END_REF], Tropidostoma was a terrestrial species [START_REF] Botha | An integrative approach to distinguishing the Late Permian dicynodont species Oudenodon bainii and Tropidostoma microtrema (Therapsida: Anomodontia)[END_REF]. The lower δ 18 Op values for Endothiodon indicate that this species had either a higher turnover of its body water as a result of more frequent drinking, or that it spent more time in water, similar to the lifestyle of extant hippopotamus [START_REF] Clementz | Identifying Aquatic Habits Of Herbivorous Mammals Through Stable Isotope Analysis[END_REF].

The sampled pareiasaur, which comes from the same stratigraphic horizon as the Endothiodon specimens, has an oxygen isotope composition almost 2‰ higher than the highest Endothiodon δ 18 Op value. As pareiasaurs have recently been shown to have been terrestrial rather than aquatic animals on the basis of their stable isotope compositions [START_REF] Rey | Oxygen isotopes and ecological inferences of Permian (Guadalupian) tetrapods from the main Karoo Basin of South Africa[END_REF], the lower values for Endothiodon corroborate its closer relationship with water.

Carbon isotopes and the diet of Endothiodon

Stratigraphic separation is also a potential problem in the comparison between δ 13 Cc values for Endothiodon and Tropidostoma in our sample. In this case δ 13 Cc values derived from Diictodon tusks do show change between the Poortjie and Hoedemaker members, and have been interpreted as reflecting a shift from arid conditions to a more humid environment [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF]Fig. 5). This interpretation comes from a decrease in δ 13 Cc values for Diictodon, so we would expect that environmental influence on our sample led to a negative

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Journal Pre-proof shift in the sampled individuals from the Hoedemaker Member (Tropidostoma) relative to the same taxon if it were sampled from the lower Poortjie Member. Our results show that δ 13 Cc values for Tropidostoma in the Hoedemaker Member are higher than those for Endothiodon in Poortjie Member so accounting for the negative environmental shift suggests an even greater disparity between the two taxa for this measurement.

The other explanation for the difference in δ 13 Cc values between Endothiodon and Tropidostoma would be a difference of diet. Whereas Endothiodon has been interpreted to have very specialized feeding habits [START_REF] Cox | On the palate, dentition, and classification of the fossil reptile Endothiodon and related genera[END_REF][START_REF] Latimer | Dentition and feeding niche of Endothiodon (Synapsida; Anomodontia[END_REF][START_REF] Cox | The jaw function and adaptive radiation of the dicynodont mammal-like reptiles of the Karoo basin of South Africa[END_REF][START_REF] Ray | Endothiodont dicynodonts from the Late Permian Kundaram Formation, India[END_REF], Tropidostoma was more likely a generalised browser [START_REF] Surkov | Head kinematics and feeding adaptations of the Permian and Triassic dicynodonts[END_REF] based on its similarity to Oudenodon [START_REF] Botha | An integrative approach to distinguishing the Late Permian dicynodont species Oudenodon bainii and Tropidostoma microtrema (Therapsida: Anomodontia)[END_REF], which was interpreted as a browser using finite element analysis of its skull [START_REF] Jasinoski | Comparative feeding biomechanics of Lystrosaurus and the generalized dicynodont Oudenodon[END_REF]. By comparing our data to published results on carbon stable isotopes, we are in a position to evaluate some of the published interpretations on the diet of Endothiodon.

Diet based on insects

The hypothesis of an insectivorous diet originated from the conical shape of the juvenile dentition and may not be applicable to the adults which have a different tooth morphology [START_REF] Ray | Endothiodont dicynodonts from the Late Permian Kundaram Formation, India[END_REF]. Tooth replacement in Endothiodon took place through successive waves [START_REF] Latimer | Dentition and feeding niche of Endothiodon (Synapsida; Anomodontia[END_REF] with new teeth forming at the posterolingual end of the row and then moving to the anterolateral end as the tooth matured [START_REF] Cox | A new endothiodont dicynodont (Therapsida, Anomodontia) from the Permian Ruhuhu Formation (Songea Group) of Tanzania and its feeding system[END_REF].

Because the replacement of teeth was steady and relatively fast [START_REF] Latimer | Dentition and feeding niche of Endothiodon (Synapsida; Anomodontia[END_REF], and because we sampled the outer layer of bone, which is the most recently mineralized zone, our results should reflect a constrained period of time preceding the death of the sampled individuals. Amongst the six sampled Endothiodon specimens, three (BP/1/7267, BP/1/7570, Insect δ 13 C values reflect their food isotopic signature [START_REF] Petelle | Insect food preferences analysed using 13 C/ 12 C ratios[END_REF][START_REF] Akamatsu | Food source of riparian spiders analyzed by using stable isotope ratios[END_REF]. Depending on the area, the season of collection [START_REF] Kato | Prey use by web-building spiders: stable isotope analyses of trophic flow at a forest-stream ecotone[END_REF], and other factors such as the island size [START_REF] Hyodo | Effect of ecosystem retrogression on stable nitrogen and carbon isotopes of plants, soils and consumer organisms in boreal forest islands[END_REF] or the species studied, the isotopic relationship between terrestrial and the aquatic food network can vary. This is a result of the greater variability in the δ 13 C of aquatic insects [START_REF] Akamatsu | Food source of riparian spiders analyzed by using stable isotope ratios[END_REF][START_REF] Kato | Prey use by web-building spiders: stable isotope analyses of trophic flow at a forest-stream ecotone[END_REF][START_REF] Paetzold | Aquatic terrestrial linkages along a braidedriver: riparian arthropods feeding on aquatic insects[END_REF]. The reason for this is that terrestrial environments prior to the Miocene were dominated by C3-plants [START_REF] Osborne | Nature's green revolution: the remarkable evolutionary rise of C4 plants[END_REF], which display a natural range of the δ 13 C values between -35‰ and -22‰ [START_REF] Kohn | Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate[END_REF], but that are generally constant in a given environment. In aquatic ecosystems, herbivorous insects can feed on algae, allochthonous terrestrial detritus, and microbial films in addition to aquatic plants, each having its own range of δ 13 C values [START_REF] Kato | Prey use by web-building spiders: stable isotope analyses of trophic flow at a forest-stream ecotone[END_REF]. The relatively narrow range of δ 13 Cc values for Endothiodon would suggest a food source with a constant δ 13 C value over time which leads us to reject aquatic insects as a food source.

Extant insectivorous mammals, such as the aardwolf or the bat-eared fox, present similar δ 13 Cc values from carbonate enamel to those of carnivorous species [START_REF] Codron | Carnivore stable carbon isotope niches reflect predator-prey size relationships in African savannas[END_REF]. Between plants and muscular tissues of herbivores, 13 C-enrichment is about 1‰ [START_REF] Barnes | Effect of temperature and ration size on carbon and nitrogen stable isotope trophic fractionation[END_REF][START_REF] Kelly | Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology[END_REF], which is the same as that observed between plants and J o u r n a l P r e -p r o o f

Journal Pre-proof insects [START_REF] Petelle | Insect food preferences analysed using 13 C/ 12 C ratios[END_REF]. The ingestion of muscular tissues and insects by predators creates a 13 C-enrichment in their bones and teeth, which is estimated to be 9-10‰ for both extant mammals [START_REF] Koch | Isotopic Study of the Biology of Modern and Fossil Vertebrates[END_REF] and reptiles [START_REF] Stanton | Stable oxygen and carbon isotope analyses of extinct archosaurs (Dinosauria) and their closest extant relatives, ratite birds and crocodylians[END_REF]. The cumulating fractionations along the food chain culminate in a 10-11‰ 13 C-enrichment in the bones of carnivorous animals relative to plants.

Several studies have revealed variations in the apatite-plant isotopic fractionation of between 10‰ and 15‰ for herbivorous mammals [START_REF] Lee-Thorp | Stable carbon isotope ratio differences between bone collagen and bone apatite, and their relationship to diet[END_REF][START_REF] Koch | Isotopic reconstruction of past continental environments[END_REF][START_REF] Cerling | Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies[END_REF][START_REF] Passey | Carbon isotope fractionation between diet, breath CO2, and bioapatite in different mammals[END_REF], whereas it is 12‰ for herbivorous reptiles [START_REF] Biasatti | Stable carbon isotopic profiles of sea turtle humeri: implications for ecology and physiology[END_REF]. Therefore, the δ 13 C values of apatite of herbivorous animals should vary between -1‰ and +5‰. However this difference might be difficult to determine in ancient extinct species [START_REF] Rey | Oxygen isotopes and ecological inferences of Permian (Guadalupian) tetrapods from the main Karoo Basin of South Africa[END_REF]. The difference recorded between the δ 13 Cc values of Endothiodon and Tropidostoma is within this range and possibly indicates a terrestrial insect diet for Endothiodon. It is also noteworthy that specialized detritivorous insects have higher δ 13 C values (up to 3‰ higher than the food substrates) and reflect fungal developme nt and humification processes in their diet [START_REF] Hyodo | Use of stable carbon and nitrogen isotopes in insect trophic ecology[END_REF]. This is in agreement with our results and thus we cannot reject the possibility that detritivorous insects formed a significant part of the diet of juvenile Endothiodon.

Diet based on heterotrophic plant components

Leaves are not the only part of the plant which are available for foraging and some dicynodonts may have subsisted on roots or other hard plant material [START_REF] King | Species longevity and generic diversity in dicynodont mammal-like reptiles[END_REF]. [START_REF] Cox | The jaw function and adaptive radiation of the dicynodont mammal-like reptiles of the Karoo basin of South Africa[END_REF] suggested that Endothiodon ate conifer cones, based on its vaulted palate that could have been used to hold cones while the lower beak extracted the seeds which were then macerated by the strange teeth present in this species. In extant C3 plants, the heterotrophic J o u r n a l P r e -p r o o f

Journal Pre-proof regions (stem, roots, seeds, and fruits) have relative 13 C-enrichment compared to the foliage [START_REF] Damesin | Carbon isotope composition of current-year shoots from Fagus sylvatica in relation to growth, respiration and use of reserves[END_REF][START_REF] Hobbie | Intramolecular, compound-specific, and bulk carbon isotope patterns in C3 and C4 plants: a review and synthesis[END_REF][START_REF] Cernusak | Why are non-photosynthetic tissues generally 13 C enriched compared with leaves in C3 plants? Review and synthesis of current hypotheses[END_REF]. Therefore, assuming that Tropidostoma was a leaf browser, the lower δ 13 C values for Endothiodon suggest that this species did not feed extensively on roots or seeds.

Diet of riverine vegetation

Another possible food source for Endothiodon is algae. Only the C3 pathway was present in Permian plants [START_REF] Osborne | Nature's green revolution: the remarkable evolutionary rise of C4 plants[END_REF] and the range of values recorded for extant members of this group is between -35‰ and -22‰ [START_REF] Kohn | Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate[END_REF]. Extant algae have δ 13 C values ranging from -23‰ to -12‰ [START_REF] Smith | Two Categories of 13 C/ 12 C Ratios for Higher Plants 1[END_REF], which is higher than that of extant terrestrial C3 plants whose range of values is between -35‰ and -22‰ [START_REF] Kohn | Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate[END_REF]. However, the lower δ 13 C values compared to Tropidostoma are not consistent with a significant algal component in the diet of Endothiodon. A better explanation is that Endothiodon subsisted on plants growing on the banks of rivers, as proposed by [START_REF] Latimer | Dentition and feeding niche of Endothiodon (Synapsida; Anomodontia[END_REF] (See Discussion 4.1). δ 13 C values in extant plants correlate with the humidity of the environment, whereby a mesic environment, such as found along the edge of watercourses, has a flora with more negative δ 13 C values than that from a xeric environment [START_REF] Garten | Foliar δ 13 C within a temperate deciduous forest: spatial, temporal, and species sources of variation[END_REF]. Even in arid areas, a wet microhabitat can flourish along rivers or at springs. In these areas, plants have lower δ 13 C values than those from the dry surrounding areas [START_REF] Kohn | Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate[END_REF]. This is consistent with the data for Endothiodon relative to Tropidostoma, whereby the latter subsisted on vegetation growing in drier environments away from river banks.

Implications for the success of Endothiodon

Endothiodon represents one of the first new taxa to appear in the Karoo Basin as part of the recovery from the Capitanian mass extinction and it is tempting to believe that its J o u r n a l P r e -p r o o f Journal Pre-proof specialised feeding system was not coincidental. [START_REF] Retallack | Middle-Late Permian mass extinction on land[END_REF] reported an increase in the abundance and diversity of lycopsid spores in the immediate aftermath of the Guadalupian (Capitanian) mass extinction, but the source of their data [START_REF] Horowitz | Palynology and paleoenvironment of uranium deposits in the Permian Beaufort Group, South Africa[END_REF] sampled only uranium-bearing horizons of uncertain stratigraphic position in the southwestern Karoo and hence are of very limited use. More recently, [START_REF] Barbolini | Palynostratigraphy of the South African Karoo Supergroup and correlations with coeval Gondwanan successions[END_REF] and [START_REF] Barbolini | A new approach to biostratigraphy in the Karoo retroarc foreland system: Utilising restricted-range palynomorphs and their first appearance datums for correlation[END_REF] presented palynomorph occurrences within the tetrapod-bearing stratigraphic units of the Beaufort Group in the southwestern Karoo, which suggested a loss of species richness between the Abrahamskraal and Teekloof formations that was up to 75% of that observed at the Permo-Triassic boundary. This resulted from the extinction of short-and medium-ranging taxa of pteridophytes, algae, and acritarchs, all of which were likely water dependent (Barbolini pers. comm.). Origination of species in the Hoedemaker Member is very low but the two that do appear, Micrhystridium stellatum and Protohaploxypinus sp., are also both water-dependent [START_REF] Barbolini | Palynostratigraphy of the South African Karoo Supergroup and correlations with coeval Gondwanan successions[END_REF]. This is consistent with results of [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF] that suggested that aridification with relatively stable temperatures had attended the Capitanian extinction in the Main Karoo Basin, with a return towards wetter conditions occurring afterwards, in the upper Poortjie Member and into the lower Hoedemaker Member. The loss of large herbivores associated with the Capitanian mass extinction may therefore have been driven, at least in part, by the loss of riparian vegetation as well as the reduction in water availability directly. As humidity within the basin increased again, it is possible that Endothiodon may have followed belts of riparian vegetation as they re-established themselves along the watercourses. While Endothiodon clearly benefited from the opportunity presented by the Capitanian mass extinctions, the role of its unique feeding system in its success remains uncertain.

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Conclusions

This work is a preliminary comparative study using stable oxygen and carbon isotope compositions of phosphate apatite of teeth and bones of the dicynodonts Endothiodon and Tropidostoma to determine their ecologies. Geochemical proxies were used to test the different ecologies proposed for Endothiodon characterized by its unique masticatory system among therapsids. Our results show significantly lower values of both δ 18 Op and δ 13 Cc for

Endothiodon when compared with those of Tropidostoma. Stable oxygen isotopes suggest that Endothiodon was more water-dependent than Tropidostoma, with a possibility that it was even semi-aquatic. Stable carbon isotopes suggest that the diet of Endothiodon did not include a substantial amount of roots, seeds or algae but rather that Endothiodon subsisted on a plant diet dominated by the mesic vegetation along watercourses, although juveniles possibly fed on terrestrial insects. Tropidostoma, by contrast, may have lived on vegetation growing in drier environments back away from river courses. Although the reasons for the success of Endothiodon in the aftermath of the Capitanian mass extinction remain unclear, these results

suggest that it could be linked to riparian vegetation.

  J o u r n a l P r e -p r o o fJournal Pre-proof Hoedemaker Member (Tropidostoma Assemblage Zone =upper Endothiodon Assemblage Zone) and Oukloof Member (Cistecephalus Assemblage Zone).

  7753) are of small size and are interpreted as juvenile or sub-adult, whereas two (BP/1/7564, BP/1/7754) are large(1.5 to two times the size of the smaller individuals) and are thus interpreted as adults. Another sampled specimen (BP/1/7356) is too fragmentary to estimate the age of the individual. No difference in the δ 13 C values is evident between the presumed adults and juveniles, indicating either a similar diet throughout ontogeny or different diets with similar δ 13 C values.

Figure 1 Figure 2 Figure 3 Figure 4

 1234 Figure 1

Figure 5

 5 Figure5

Acknowledgments

The authors thank the South African Heritage Resources Agency (SAHRA) for their authorization to sample the fossils, and export sub-samples for stable isotope analysis of phosphate (PermitID: 2541). Marion Bamford, Bernhard Zipfel and Sifelani Jirah are acknowledged for access to the Karoo fossil collections of the ESI and for sanction to sample the tetrapod fossils. We also acknowledge Anne Westoby for the figures of the skulls. This work was supported by the Palaeontological Scientific Trust (PAST) and its Scatterlings of J o u r n a l P r e -p r o o f

Africa programmes, National Research Foundation (NRF) African Origins Platform of South Africa (grant no. 98802) and DST/NRF Centre of Excellence in Palaeosciences. -p r o o f Journal Pre-proof

Figure and table captions

together with the empirical isotopic equilibrium line [START_REF] Iacumin | Oxygen isotope analyses of coexisting carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate? Earth Planet[END_REF] with a slope close to unity (bold line). The altered samples are within the circle. The reduced major axis regression lines are represented for all samples (dash line) except unaltered ones (full line). [START_REF] Rey | Stable isotope record implicates aridification without warming during the late Capitanian mass extinction[END_REF]. Skull figures are from [START_REF] Day | Biostratigraphy of the Endothiodon Assemblage Zone[END_REF] and [START_REF] Day | Biostratigraphy of the Tapinocephalus Assemblage Zone[END_REF], published with permission from the Geological Society of South Africa. All scale bars represents 10 cm.

Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

J o u r n a l P r e -p r o o f Journal Pre-proof Highlights:

-Stable isotopes allow understanding palaeobiology and lifestyle of Permian tetrapods.

-Oxygen stable isotopes indicate Endothiodon was more water-dependent than Tropidostoma.

-Carbon Stable isotopes reveal dicynodont Endothiodon fed on riverine vegetation.

-Stable carbon isotopes show diet of juvenile Endothiodon probably included insects.

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