Diying Huang
email: dyhuang@nigpas.ac.cn

Dany Azar
email: azar@mnhn.fr

Chenyang Cai

Sibelle Maksoud

André Nel
email: anel@mnhn.fr

Günter Bechly
email: guenter.bechly@smns-bw.de

Mesomegaloprepidae, a remarkable new damselfly family (Odonata: Zygoptera) from mid-Cretaceous Burmese amber

Keywords:

Introduction

Descriptions of fossil damselflies in Cretaceous amber were relatively rare until the recent palaeoentomological studies on the mid-Cretaceous amber from Myanmar, work which has already resulted in the description of seven species from the families Hemiphlebiidae, Perilestidae, Dysagrionidae, Platystictidae, and Platycnemididae [START_REF] Poinar | First record of Odonata and a new subfamily of damselflies from early Cretaceous Burmese amber[END_REF][START_REF] Huang | New damselfly genera in the Cretaceous Burmese amber attributable to the Platystictidae and Platycnemididae Disparoneurinae (Odonata: Zygoptera)[END_REF]Zheng et al., 2016a, b, c, in press), with further descriptions in preparation by the authors.

Here, we describe a remarkable new fossil damselfly taxon, Mesomegaloprepus magnificus gen. et sp. nov. (Zygoptera: Mesomegaloprepidae fam. nov.) (Fig. 1), from eight amber pieces with more than 14 conspecific inclusions in 99 Ma Burmese amber. This fossil shows curious similarities with the extant tropical families Thaumatoneuridae and Pseudostigmatidae, giving us an occasion to discuss the position of the fossil taxa currently considered in these two clades (see Supplementary material).

Materials and methods

Fossils were examined and measured using an incident light stereomicroscope (Olympus SZX9) and a stereomicroscope (Nikon SMZ 1500), as well as a Leitz Wetzlar binocular microscope. Photographs were taken using a Zeiss Discovery V20 microscope system. Optical instruments were equipped by camera lucida and digital cameras. The raw digital images were processed with focus stacking software, and figure plates prepared with Adobe Photoshop TM .

We follow the wing venation nomenclature of [START_REF] Riek | A new interpretation of dragonfly wing venation based upon Early Carboniferous fossils from Argentina (Insecta: Odonatoidea) and basic characters states in pterygote wings[END_REF], emended by [START_REF] Nel | Les 'Anisozygoptera' fossiles. Phylogénie et classification (Odonata)[END_REF] and [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF]. The higher classification of fossil and extant Odonatoptera, as well as characters for family diagnoses, are largely based on the phylogenetic system proposed by [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF]. Several recent works that have addressed the higher phylogeny of Zygoptera [START_REF] Dumont | A molecular phylogeny of the Odonata (Insecta)[END_REF][START_REF] Davis | Fossil gaps inferred from phylogenies alter the apparent nature of diversification in dragonflies and their relatives[END_REF][START_REF] Dijkstra | The classification of dragonflies and damselflies (Odonata)[END_REF][START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF] have been taken into account.

Burmese amber

The specimens are preserved in eight pieces of relatively clear, yellow Burmite amber.

The amber pieces were polished before being examined and photographed. The amber piece with paratype NIGP 161753 has been included in a glass coffin with Canada Balsam as medium for better examination. All amber material was legally acquired in Myanmar from local traders with government registration, and legally exported according to the official regulations in Myanmar.

Fossil-bearing has mostly been collected from the Hukawng Valley in northern Myanmar (formerly known as Burma). For an overview of the amber deposit and its geological setting see, e.g., [START_REF] Zherikhin | A review of the history, geology and age of Burmese amber (Burmite)[END_REF], [START_REF] Grimaldi | Fossiliferous Cretaceous amber from Myanmar (Burma): its rediscovery, biotic diversity, and paleontological significance[END_REF], [START_REF] Cruickshank | Geology of an amber locality in the Hukaung Valley, northern Myanmar[END_REF], and [START_REF] Ross | Burmese amber[END_REF]. Radiometric U-Pb zircon dating [START_REF] Shi | Age constraints on Burmese amber based on U-Pb dating of zircons[END_REF] recently constrained this amber to a minimum age of 98.79±0.62 Ma, which is equivalent to the mid-Cretaceous (earliest Cenomanian). The original habitat of the amber forest is still controversial, in fact it has originally been assumed to be a tropical araucarian forest [START_REF] Grimaldi | Fossiliferous Cretaceous amber from Myanmar (Burma): its rediscovery, biotic diversity, and paleontological significance[END_REF][START_REF] Poinar | Araucarian source of fossiliferous Burmese amber: spectroscopic and anatomical evidence[END_REF], possibly with Dipterocarpaceae as another source for the fossil resin. However, the first detailed report on the macromolecular nature and palaeobotanical affinity of Burmite [START_REF] Dutta | Terpenoid composition and botanical affinity of Cretaceous resins from India and Myanmar[END_REF], based on gas chromatography -mass spectrometry, rejected Araucariaceae and Dipterocarpaceae in favour of Pinaceae as the Burmese amber tree. [START_REF] Grimaldi | Diverse orthorrhaphan flies (Insecta: Diptera: Brachycera) in amber from the Cretaceous of Myanmar: Brachycera in Cretaceous amber, Part VII[END_REF], after Grimaldi and Ross (in press), considered 'based on the abundant inclusions of leafy shoots' that it was formed by a conifer, and 'amber produced possibly by Metasequoia (Taxodiaceae) or a close relative'. Even though fossil and extant Pinaceae are generally absent from south of the equator and from tropical rainforests in particular, a notable exception is Pinus krempfii from the rainforests of Vietnam [START_REF] Brodribb | Evolutionary significance of a flat-leaved Pinus in Vietnamese rainforest[END_REF].

The family, genus, and species are registered in Zoobank under the urn:lsid:zoobank.org:act:CFC6346B-B702-4A83-B436-6D3730E73C9C

Systematic palaeontology

Order Odonata Fabricius, 1793 Suborder Zygoptera Selys, 1854 Family Mesomegaloprepidae fam. nov.

Type-genus. Mesomegaloprepus gen. nov.

Diagnosis. As for the genus, since it is presently monotypic (see below). Type-locality and stratum. Tanai Village, Hukawng Valley, Kachin State, northern Myanmar. Burmite, mid-Cretaceous (earliest Cenomanian), ca. 99 Ma [START_REF] Shi | Age constraints on Burmese amber based on U-Pb dating of zircons[END_REF].

Genus

Diagnosis. As for the genus, since it is presently monotypic (see above), wings dark brown with a hyaline apex, in males with posterior hyaline patch in distal cubital area, and in females with narrow hyaline transverse band near base of RP2 (sexual dimorphism).

Descriptions.

Holotype female NIGP 164902. A head and thorax with three wings attached. Wings basal halves dark brown, then a narrow hyaline transverse zone, followed by a second dark zone and wing apex hyaline; forewing ca. 29.0 mm long (preserved part 26.0 mm long), 8.7 mm wide, 3.7 mm wide at nodus level; distance from base to arculus 2.4 mm, from arculus to nodus 3.2 mm; nodus in a basal position, more than 19% of wing length; petiole very short, 0.8 mm long, 1.0 mm wide; distance from base to Ax1 1.8 mm, from Ax1 to Ax2 0.8 mm; arculus distinctly basal of Ax2; 3 accessory secondary antenodal crossveins between C and ScP distal of Ax2, but none between ScP and RA; antesubnodal space with a regular series of crossveins; numerous postnodal crossveins not well aligned with postsubnodal crossveins; pterostigma present but not colored, no pterostigmal brace; bases of RP3/4 and IR2 (midfork) basally recessed midway between arculus and nodus; IR2 apparently arising on RP3/4; basal space between RP3/4 and IR2 not narrowed; area between RP and MA between arculus and base of RP3/4 without a crossvein; base of RP2 far distal from subnodus; no oblique crossvein; two secondary longitudinal veins between MA and MP in distal part, both apparently emerging from MP; discoidal cell crossed, rectangular, with MAb of inverted obliquity; subdiscoidal cell traversed by two crossveins; CuP between M+Cu and AA; anal area rather wide with a series of small transverse cells between AA and AP; cubital area broad, CuA long with numerous curved posterior branches and characteristically triadic branching pattern of CuA; area between MP and CuA broader than postdiscoidal area in their basal parts; no intercalary vein between MP and CuA.

Allotype NIGP161753. The amber piece is 3.5 cm long and 0.5 cm wide. This specimen (Figs. 23) features head, thorax, and the four basal abdominal segments, two fore legs, one mid leg, one hind leg, two-third of left forewing and bases of the two hind wings attached. Head transverse, 5.0 mm wide, with eyes well separated, distance between eyes ca. 4.0 mm; ocelli disposed in triangle on a low protuberance between eyes. Legs with long spines on femora and tibiae. Abdomen ca. 2.0 mm wide (it is not visible if there is a secondary copulatory apparatus on the second segment or not). Forewing uniformly dark brown owing oxidation; forewing ca. 29.0 mm long (preserved part 26.0 mm long), 8.7 mm wide, 3.7 mm wide at nodus level; distance from base to arculus 2.4 mm, from arculus to nodus 3.2 mm; nodus in a basal position, more than 19% of wing length; petiole very short, 0.8 mm long, 1.0 mm wide; distance from base to Ax1 1.8 mm, from Ax1 to Ax2 0.8 mm; arculus distinctly basal of Ax2; 3 accessory secondary antenodal crossveins between C and ScP distal of Ax2, but none between ScP and RA; antesubnodal space with a regular series of crossveins; numerous postnodal crossveins not well aligned with postsubnodal crossveins; pterostigma present but not colored, no pterostigmal brace; bases of RP3/4 and IR2 (midfork) basally recessed midway between arculus and nodus; IR2 apparently arising on RP3/4; basal space between RP3/4 and IR2 not greatly narrowed; area between RP and MA between arculus and base of RP3/4 with a crossvein; base of RP2 far distal from subnodus; no oblique crossvein; two secondary longitudinal veins between MA and MP in distal part, both apparently emerging from MP; discoidal cell crossed, rectangular, with MAb of inverted obliquity; subdiscoidal cell traversed by two crossveins; CuP between M+Cu and AA; anal area rather wide with a series of small transverse cells between AA and AP; cubital area broad, CuA elongate with numerous curved posterior branches and characteristically triadic branching pattern of CuA; area between MP and CuA broader than postdiscoidal area in their basal parts; no intercalary vein between MP and CuA.

Paratype NIGP 161754. The amber piece with this paratype is 2.6 cm long and 0.5 cm wide. This specimen (Fig. 2e-f) features fragments of thorax with part of head and first basal abdominal segments still attached, plus bases of the two right wings and the basal half of left forewing. The preserved parts of wing are nearly identical in proportions and venation to those of the holotype, documenting the conspecific status. Head transverse with eyes well separated. Thorax ca. 2.8 mm wide and ca. 4.0 mm high. Abdomen 2.0 mm wide; no secondary copulatory apparatus on segments 2-3 (thus a female specimen). Forewing dark brown with a narrow lighter transverse band distal of nodus, near base of RP2, forewing with preserved part ca. 18.0 mm long, 3.3 mm wide at nodus level; distance from base to nodus 4.4 mm, nodus in a very basal position; petiole very short, 1.2 mm long; Ax2 about opposite arculus; area between RP and MA between arculus and base of RP3/4 without any crossvein.

Paratype NIGP 164903. This specimen features a nearly complete abdomen of a male, with a nearly complete hind wing attached to fragments of the thorax and two wing apices, as well as isolated legs with very long spines. It has the same proportions and wing venation as the holotype (including arculus distinctly basal of Ax2); nevertheless its area between RP and MA between arculus and base of RP3/4 is without any crossvein. The wing has a brown colour pattern except for the translucent apex and distal cubital area. This specimen clearly shows the male secondary copulatory apparatus of abdominal segment 2, with a ligula having its distal segment modified to form a very long single flagellum, reaching segment 3; a series of strong spines on the genital lobes; anterior hamuli well developed with a smooth point.

Paratype NIGP 164950. This specimen features 10 isolated wings of male and female specimens that probably represented a mating group. The wings are largely identical to those of the allotype NIGP 161753 (including arculus distinctly basal of Ax2), except in the area between RP and MA between arculus and base of RP3/4 without any crossvein. The colour pattern is similar to the other specimens.The Pterostigmata are covering 2.5-3.5 narrow cells beneath them.

Paratype NIGP 164951. This specimen features six isolated wings (probably of a mating pair) without preserved bodies. The wings are also identical to the holotype. The colour patterns are similar to those of the other specimens.

Paratype male NIGP 164904. This specimen features a male with head, thorax and part of the abdomen, plus wings. The wings are also identical to the holotype. The colour patterns are similar to those of the other specimens.

Paratype SMNS Bu-231. This specimen features partially preserved bodies of three specimens (incl. male and female), with fragments of all wings and legs bearing very long spines. The wing venations are very similar to those of the allotype (including arculus distinctly basal of Ax2) and the colour pattern is similar to those of the other specimens.

Notable differences are: antesubnodal space with seven crossveins but no crossveins in the basal third (right wings of female); midfork (origin of IR2 and RP3/4) is not in midway position between subnodus and arculus but further recessed close to arculus (right hind wing of female); subdiscoidal cell traversed by two crossveins in the forewing, but only one in the hind wing (right wings of female); pterostigma covering three narrow cells beneath it (in the female).

Discussion

Phylogenetic relationships

Placement of Mesomegaloprepidae fam. nov. is challenging owing to conflicting evidence. Mesomegaloprepus gen. nov. shows venational similarities with three different known family-group taxa of Neotropical damselflies, viz. Latibasaliidae (genus Latibasalia [START_REF] Petrulevičius | A new damselfly family from the Upper Palaeocene of Argentina[END_REF], Coenagrionidae-Pseudostigmatinae (esp. genus Megaloprepus), and Thaumatoneuridae (esp. genus Thaumatoneura McLachlan, 1897). [START_REF] Petrulevičius | A new damselfly family from the Upper Palaeocene of Argentina[END_REF] Latibasaliidae (Zygoptera: Amphipterygoidea) are an enigmatic fossil family from the Paleogene (Upper Palaeocene) of Argentina (Petrulevičius andNel 2004, 2007). A potential relationships with the fossil genera Petrolestes Cockerell, 1927 and[START_REF] Zhang | Early Cretaceous, Laiyang, China) Subfamily incertae sedis Palaeodysagrion Zheng et al[END_REF] (Amphipterygoidea: Thaumatoneuridae) was discussed in the original description, because they share the absence of secondary antenodal crossveins and the absence of antesubnodal crossveins. However, these characters are very homoplastic and weak. We transfer here Latibasaliidae from Amphipterygoidea to Epallagoidea as sister group of Zacallitidae, because of the shared convex longitudinal intercalary vein in the cubital field as unique putative synapomorphy. The mentioned differences in Mesomegaloprepus are all derived states that could be autapomorphies; so they would not contradict a relationship with Latibasaliidae. However, many of the similarities are either of uncertain polarity, or symplesiomorphies, or homoplastic, so that the evidence for a relationship is weak and inconclusive. We therefore can neither exclude nor establish a sister group relationship of Mesomegaloprepidae with Latibasaliidae. Nevertheless, the densely reticulated wings with short petiolus, and especially the rectangular shape of the discoidal cell with a distal side MAb with reversed obliquity would support a position in Epallagoidea (new position for Latibasaliidae), and the expanded cubital field would agree with Zacallitidae (here recognized as sister group of Latibasaliidae).

Comparison with Latibasaliidae

Mesomegaloprepus

Furthermore, the recession of the midfork, the reduced pterostigmal brace and lestine oblique vein 'O', as well as the coloured wings would support a position in Caloptera (Calopterygoidea sensu [START_REF] Dijkstra | The classification of dragonflies and damselflies (Odonata)[END_REF], if this group is monophyletic at all, which is rather doubtful [START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF]. [START_REF] Dijkstra | The classification of dragonflies and damselflies (Odonata)[END_REF] Pseudostigmatinae (formerly classified as distinct family Pseudostigmatidae) is a group of mainly Neotropical giant damselflies (also known as helicopter damselflies) that oviposit in phytotelmata, where the dendrolimnetic larvae develop. Adults pluck orb-weaver spiders and their prey from spider webs [START_REF] Fincke | Giant damselflies in a tropical forest: reproductive biology of Megaloprepus coerulatus with notes on Mecistogaster (Zygoptera: Pseudostigmatidae)[END_REF]Clausnitzer, 2002). The extremely long abdomen is apparently not developed for oviposition in phytotelmata but used as balance while hovering in front of spider webs (Clausnitzer, 2002). The only Pseudostigmatinae outside of the Neotropical realm is the Eastern African Coryphagrion grandis [START_REF] Morton | A new genus and new species of dragonfly from East Africa belonging to the legion Podagrion (Odonata)[END_REF] which was formerly classified in a monotypic separate family Coryphagrionidae Pinhey, 1962, but recognized as most closely related to or belonging to Pseudostigmatinae by [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF], [START_REF] Clausnitzer | Natural history and description of the dendrolimnetic larvae of Coryphagrion grandis (Odonata)[END_REF], [START_REF] Rehn | Phylogenetic analysis of higher-level relationships of Odonata[END_REF], [START_REF] Groeneveld | Convergent evolution of gigantism in damselflies of Africa and South America? Evidence from nuclear and mitochondrial sequence data[END_REF], [START_REF] Yu | A preliminary phylogenetic study of Megapodagrionidae with focus on the Chinese genera Sinocnemis Wilson & Zhou and Priscagrion Zhou & Wilson (Odonata: Zygoptera)[END_REF][START_REF] Yu | A preliminary phylogenetic study of Megapodagrionidae with focus on the Chinese genera Sinocnemis Wilson & Zhou and Priscagrion Zhou & Wilson (Odonata: Zygoptera)[END_REF][START_REF] Ingley | Life on the fly: phylogenetics and evolution of the helicopter damselflies (Odonata, Pseudostigmatidae)[END_REF]. Coryphagrion Morton, 1924 is very similar to Mecistogaster Rambur, 1842. Like all Neotropical Pseudostigmatinae, it oviposits in phytotelmata and exclusively feeds on spiders and insects picked out of spider webs [START_REF] Lounibos | Larval Odonata in water-containing treeholes at the Kenya coast[END_REF]Clausnitzer, 2002;[START_REF] Clausnitzer | Natural history and description of the dendrolimnetic larvae of Coryphagrion grandis (Odonata)[END_REF]. All Neotropical genera have a more or less reduced pterostigma and males have characteristical hamuli anteriores and a terminal single flagellum on the ligula [START_REF] Schmidt | Vergleichende Morphologie des 2. und 3. Abdominalsegments bei männlichen Libellen[END_REF][START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF], while Coryphagrion has retained a normal pterostigma and lacks the terminal ligula flagellum [START_REF] Kimmins | Description of the male of Coryphagrion grandis Morton (Odonata)[END_REF][START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF]. Morphological and genomic data have shown that the Pseudostigmatinae (incl. Coryphagrion) nest deeply within Coenagrionidae and thus should be classified within this family [START_REF] Ramírez | Description and natural history of the Costa Rican Odonata larvae. 5. Megaloprepus caerulatus (Drury, 1782) (Zygoptera, Pseudostigmatidae)[END_REF][START_REF] Bybee | Molecules, morphology and fossils: a comprehensive approach to odonate phylogeny and the evolution of the odonate wing[END_REF][START_REF] Carle | Evolution of Odonata, with special reference to Coenagrionoidea (Zygoptera)[END_REF][START_REF] Yu | A preliminary phylogenetic study of Megapodagrionidae with focus on the Chinese genera Sinocnemis Wilson & Zhou and Priscagrion Zhou & Wilson (Odonata: Zygoptera)[END_REF][START_REF] Ingley | Life on the fly: phylogenetics and evolution of the helicopter damselflies (Odonata, Pseudostigmatidae)[END_REF][START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF]. [START_REF] Dijkstra | The classification of dragonflies and damselflies (Odonata)[END_REF] therefore formally sunk the family Pseudostigmatidae in Coenagrionidae, where it forms a subfamily Pseudostigmatinae with three tribes [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF][START_REF] Ingley | Life on the fly: phylogenetics and evolution of the helicopter damselflies (Odonata, Pseudostigmatidae)[END_REF] character distribution shows that narrow wings without triadic branchings represent the plesiomorphic ground plan condition, from which derived broad winged forms evolved [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF][START_REF] Ingley | Life on the fly: phylogenetics and evolution of the helicopter damselflies (Odonata, Pseudostigmatidae)[END_REF]. The extant genus Megaloprepus represents the largest known damselfly of all times with a wingspan of up to 19 cm and an abdomen length of 10 cm [START_REF] Groeneveld | Convergent evolution of gigantism in damselflies of Africa and South America? Evidence from nuclear and mitochondrial sequence data[END_REF].

Comparison with Pseudostigmatinae Kirby, 1890 (sensu

Putative synapomorphies of Mesomegaloprepus with Pseudostigmatinae (incl.

Coryphagrionini) are as follows: similar shape of wing with very dense venation and a large number of cells (also present in Thaumatoneura); very basal position of nodus at about 20% of wing length (also present in Thaumatoneura), correlated with a basal recession of the midfork at about 25% of wing length, and a high number of postnodal veins and an origin of RP2 far distal of subnodus; discoidal cell elongated (also present in Thaumatoneuridae); IR2 apparently arising from RP3/4 (as in Thaumatoneuridae); more than two rows of cells between RP1 and RP2 (also present in Thaumatoneura), with very long IR1 and a shorter negative intercalary between IR1 and RP1 (very much like Pseudostigmatinae, and unlike Thaumatoneura); pterostigma very short, rectangular, and in apical position. Finally the possible association with phytotelmata (see below) might represent evidence for a relationship with Pseudostigmatinae (incl. Coryphagrion), but also occurs by convergence in some unrelated tropical damselfly and dragonfly taxa. However, the following plesiomorphies of Mesomegaloprepus contradict a placement within the crown group of Pseudostigmatinae or even in Coenagrionoidea: much smaller size (all Pseudostigmatinae show gigantism); presence of three accessory secondary antenodal crossveins between C and ScP distal of Ax2 (unknown in Coenagrionoidea, but 1-2 present in Thaumatoneura); multiple antesubnodal crossveins (unknown in Coenagrionoidea); postnodal and postsubnodal crossveins not aligned (unknown in Coenagrionoidea, but present in Thaumatoneura); RA and RP1 not sigmoidally curved at apex, and RP1 and RP2 not converging apically; basal part of space between IR2 and RP3/4 not strongly narrowed; only a single row of cells between C and RA at apex (two or more rows in Pseudostigmatinae, except for some but not all specimens of Coryphagrion and Mecistogaster, but also Thaumatoneuridae). Mesomegaloprepus differs from nearly all known Coenagrionidae (including all Pseudostigmatinae), with the sole exception of Protoneurinae s.str. (subfamily of Coenagrionidae according to [START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF], in the rectangular shape of the discoidal cell (as in Thaumatoneura, and less developed in Megaloprepus). Also Mesomegaloprepus differs from all known Coenagrionoidea (including all Pseudostigmatinae) in the position of the arculus distinctly basal of Ax2 (but the polarity of this character is unclear), the recession of the midfork (origins of IR2 and RP3/4) distinctly basal of subnodus (a derived state that never occurs in Coenagrionoidea and Thaumatoneuridae, but is typical for Lestoidea and "Calopterygoidea"), and the presence of several secondary (intercalary) longitudinal veins in the median and radial areas (as in Thaumatoneuridae).

Putative synapomorphies with Neotropical Pseudostigmatinae (Pseudostigmatini + Megaloprepini)) are as follows: pterostigmal brace reduced (as in Thaumatoneura; still braced in Coryphagrion); male secondary genital apparatus with distal segment of ligula modified into a very long single flagellum (absent in Coryphagrion). The following plesiomorphies of Mesomegaloprepus contradict a placement in the crown group of Neotropical Pseudostigmatinae: RA, RP1, and IR1 not apically strongly curved towards the hind margin and converging to the same point at the hind margin (only reversed in Anomisma); only a single row of cells between RP1 and IR1 (like Coryphagrion, but unlike all other Pseudostigmatinae and Thaumatoneuridae); normal pterostigma present (replaced by pseudopterostigma in all Neotropical Pseudostigmatinae). The very short parallel-sided pterostigma of Mesomegaloprepus could be interpreted as precursor of the further reduction of the pterostigma in Neotropical Pseudostigmatinae, but the presence of a normal pterostigma rather than a pseudo-pterostigma would still exclude any position within the crown group Pseudostigmatinae and especially any closer relationship with Megaloprepus.

Putative synapomorphies with broad-winged Pseudostigmatinae (Megaloprepini) are as follows: broad shape of wings; CuA very long with numerous curved posterior branches, and triadic branching pattern of CuA (also present in Thaumatoneura); furcation of RP into RP1 and RP2 shifted into distal half of wing, thus base of RP2 very far distal of subnodus (as in Thaumatoneura). However, the following plesiomorphies of Mesomegaloprepus contradict a placement in the crown group of the broad-winged Pseudostigmatinae and thus refute a potential sister group relationship with either Anomisma or Megaloprepus: pterostigma present; absence of the typical triadic branching of apical MA, and apical furcation of RP3/4; distally only a single row of cells between RA and RP (at least two rows in Megaloprepini, but also at apex of Thaumatoneuridae); only a single row of cells between RP1/2 and RP3/4 between the RP forks (as in Thaumatoneuridae).

Putative synapomorphies with the extant genus Anomisma (Pseudostigmatinae: Megaloprepini) are as follows: discoidal cell divided (unique autapomorphy within Coenagrionidae, and unlike the undivided discoidal cell in Thaumatoneura); subdiscoidal cell divided by two crossveins (vs only one in Thaumatoneura); presence of at least one accessory secondary antenodal crossvein between C and ScP distal of Ax2 (unique reversal within Coenagrionidae, also present in Thaumatoneura). However, Anomisma has a very different discoidal cell that is very elongate (instead of short), acute (instead of rectangular), and divided by 2-3 (instead of only one) crossveins. Also, Anomisma has only a single accessory secondary antenodal crossvein instead of three. These differences may suggest a case of convergence rather than synapomorphy, especially since these two characters are highly homoplastic within Zygoptera. [START_REF] Kalkman | Generic revision of the Argiolestidae (Odonata), with four new genera[END_REF], so that it also represents a weak and conflicting character. Consequently, there is no conclusive evidence to establish a phylogenetic relationship of Mesomegaloprepus with the Pseudostigmatinae. [START_REF] Tillyard | Paraphlebia Selys 1862 (Paraphlebia as used by Hagen, 1861 is a nomen nudum according to Garrison[END_REF]Fraser, 1938 (sensu Dijkstra, 2014) Recent Thaumatoneuridae are endemic to the Neotropics and only include the two genera Thaumatoneura McLachlan, 1897 (one species T. inopinata) and Paraphlebia Selys, 1862 (four species) [START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF] from Central America, which all are relatively large damselflies typically found in the vicinity of waterfall habitats ("waterfall damsels"). Females have hyaline wings, while males are typically dimorphic with either hyaline wings or distinct dark colour pattern [START_REF] Calvert | Studies on Costa Rica Odonata. V. The waterfall-dwellers: Thaumatoneura imagos and possible male dimorphism[END_REF][START_REF] González-Soriano | Sexual behaviour in Paraphlebia quinta Calvert: male dimorphism and a possible example of odonate female control (Zygoptera: Megapodagrionidae)[END_REF][START_REF] Romo-Beltrán | Male dimorphism, territoriality and mating success in the tropical damselfly, Paraphlebia zoe Selys (Odonata: Megapodagrionidae)[END_REF].

Putative synapomorphies with the extant genus Megaloprepus

Comparison with Thaumatoneuridae

A close relationship of the Recent genera Thaumatoneura and Paraphlebia was previously suggested based on adult and larval morphology [START_REF] Novelo-Gutiérrez | Description of the larva of Paraphlebia zoe Selys in Hagen, 1861 (Odonata: Megapodagrionidae)[END_REF][START_REF] Garrison | Damselfly genera of the New World, an illustrated and annotated key to the Zygoptera[END_REF]. It has been confirmed with modern phylogenomic studies [START_REF] Fogarty | Phylogenetic relationships of Central and South American flatwing damselflies (Odonata: Zygoptera: Megapodagrionidae): An examination of monophyly in a convoluted group[END_REF][START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF]. [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF] considered that the Thaumatoneuridae are related to the Amphipterygoidea within the jewelwing clade Eucaloptera (Calopterygoidea sensu [START_REF] Dijkstra | The classification of dragonflies and damselflies (Odonata)[END_REF]. [START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF] suggested a somewhat different phylogeny for Thaumatoneuridae in a clade that comprises several genera previously considered as "Megapodagrionidae", and this whole clade being sister group of a clade that comprises the Philogeniidae, Amphipterygidae, Lestoideidae, and Epallagidae (= Euphaeidae).

The fact that two South East Asian "megapodagrionid" damselfly genera (viz.

Bornargiolestes Kimmins, 1936 andBurmargiolestes Kennedy, 1925) have been proposed by [START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF] as closest relatives of Thaumatoneuridae, could suggest that a stem-Thaumatoneuridae from Burmese amber would not be an unlikely discovery.

All fossil taxa that previously have been attributed to Thaumatoneuridae are rather of dubious relationship and are revised below.

Putative synapomorphies of Mesomegaloprepus with extant Thaumatoneuridae (Paraphlebia + Thaumatoneura) (see [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF] are as follows: dark banded colour pattern of wings with sexual dimorphism (as in Megaloprepus); dense wing venation with several hundreds of cells; nodus in very basal position, correlated with large number of postnodal crossveins (as in Pseudostigmatinae); triadic branching of CuA; subdiscoidal cell traversed by a crossvein; discoidal cell elongated (as in Pseudostigmatinae); IR2 apparently arising from RP3/4 (as in Pseudostigmatinae); presence of several secondary (intercalary) longitudinal veins in median and radial area. Nevertheless, the following plesiomorphies of Mesomegaloprepus contradict a placement in the crown group of Thaumatoneuridae: small size; several antesubnodal crossveins; only a single row of cells between RA and RP1 distal of pterostigma; absence of intercalary veins between MP and CuA. Mesomegaloprepus strongly differs from Thaumatoneuridae in the divided discoidal cell, as well as the very short and rectangular pterostigma, while the discoidal cell of Paraphlebia and Thaumatoneura is always undivided and their pterostigmata are very long with a extremely oblique basal side (but also unbraced, which seems to be a symplesiomorphy of Thaumatoneuridae, as the pterostigma of closely related genera like Burmargiolestes is also unbraced). Also the fact that the midfork is not basally recessed between arculus and subnodus in extant Thaumatoneuridae contradicts a relationship with Mesomegaloprepus Further important differences are the position of arculus that is more or less aligned with Ax2 in Thaumatoneuridae but distinctly basal of Ax2 in Mesomegaloprepus, as well as the position of the CuP-vestige ("anal crossing") that is located in the petiolus in Thaumatoneuridae, while it ends on free vein AA distal of petiolus in Mesomegaloprepus, but the polarity of these two characters is uncertain.

An antesubnodal space without any crossveins was proposed by [START_REF] Bechly | Odonata: damselflies and dragonflies[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF] as an autapomorphy of Thaumatoneuridae, but of course this character is highly homoplastic and also present in all Lestoidea and Coenagrionoidea (incl. Pseudostigmatinae), but it is absent in

Mesomegaloprepus.

Putative synapomorphies with only the extant genus Thaumatoneura: broad wings with very dense wing venation (large number of cells) (as in Pseudostigmatinae:

Megaloprepini); petiolus very short (still long in Paraphlebia); nodus even in more basal position, correlated with large number of postnodal crossveins; presence of a few accessory secondary antenodal crossveins between C and ScP distal of Ax2 (3 in Mesomegaloprepus, 1-2 in Thaumatoneura, none in Paraphlebia); discoidal cell rectangular with distal side MAb with reversed obliquity (still acute in Paraphlebia); subdiscoidal cell traversed by 1-2 crossveins (however the subdiscoidal cell of Thaumatoneura is of very different shape and much longer); postnodal and postsubnodal crossveins secondarily non-aligned (still aligned in Paraphlebia); greatly expanded cubital area; CuA with numerous curved posterior branches and characteristical triadic branching pattern of CuA (similar to Megaloprepus, but CuA much shorter); longitudinal veins distally distinctly curved towards hind margin of wing; base of RP2 very far distal of subnodus as in Pseudostigmatinae: Megaloprepini). In the anal area of Mesomegaloprepus, there is a series of small transverse cells between AA and AP below the subdiscoidal space, which is a character state also present in Thaumatoneura, but the Pseudostigmatinae also have small crossveins in the anal area between AA and AP below the subdiscoidal space. However, the anal area is distinctly narrower in Pseudostigmatinae than in Mesomegaloprepus and Thaumatoneura, but it is even narrower in Paraphlebia (second modern genus of Thaumatoneuridae). Even though all these character states seem to be derived in Thaumatoneura, as suggested by the more "megapodagrionid"-like sister genus Paraphlebia and the closely related genera Bornargiolestes and Burmargiolestes as sistergroups, the character polarity is unclear in Mesomegaloprepus, mainly because of the homoplastic distribution of these character states in other damselfly taxa (e.g., multiple secondary antenodal crossveins is generally rather a plesiomorphy in odonates). The fact that other characters (see above) contradict an ingroup position of Mesomegaloprepus within Thaumatoneuridae as sister group of Thaumatoneura, rather suggests that the similarities between these two genera are not synapomorphies.

Mesomegaloprepus strongly differs from the other extant thaumatoneurid genus

Paraphlebia in the rectangular and divided discoidal cell, very short petiolus, broad cubital area, and nodus even more strongly basally recessed.

Ambiguous relationship of Mesomegaloprepidae and justification for this new family

Mesomegaloprepus shows a confusing mosaic of characters shared by either the thaumatoneurid genus Thaumatoneura or the pseudostigmatine genus Megaloprepus, or present in both (sub)families. Mesomegaloprepus differs from the modern representatives of the Thaumatoneuridae and Pseudostigmatinae in the much smaller size, the vestige of vein CuP ("anal crossing") between M+Cu and AA instead of being between M+Cu and A, the presence of antesubnodal crossveins, and bases of RP3/4 and IR2 (midfork) basally recessed midway between arculus and nodus instead of being aligned with the subnodus. These differences, as well as the conflicting and thus probably convergent similarities with Latibasaliidae, Thaumatoneuridae, and Pseudostigmatinae, allow us to erect a new family Mesomegaloprepidae, with unresolved relationship within Zygoptera. If Mesomegaloprepidae should turn out to belong to one of the discussed extant family group taxa after all, it could be reclassified as distinct subfamily or tribe within them.

Anyway, the high degree of character conflicts in the wing venational similarities with Thaumatoneura on the one hand and broad-winged Pseudostigmatinae-Megaloprepini on the other hand, while lacking more superordinate ground-plan characters of the family group taxa Thaumatoneuridae and Pseudostigmatinae, is a strong indication that wing venational characters generally are of poor value for the reconstruction of phylogenetic relationships within Odonata. This is also indicated by the strong difference between phylogenetic classifications of damselflies based on wing venational characters [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF] with those based on modern phylogenomic studies [START_REF] Bybee | Molecules, morphology and fossils: a comprehensive approach to odonate phylogeny and the evolution of the odonate wing[END_REF][START_REF] Carle | Evolution of Odonata, with special reference to Coenagrionoidea (Zygoptera)[END_REF][START_REF] Dumont | A molecular phylogeny of the Odonata (Insecta)[END_REF][START_REF] Dijkstra | The classification of dragonflies and damselflies (Odonata)[END_REF][START_REF] Dijkstra | Redefining the damselfly families: a comprehensive molecular phylogeny of Zygoptera (Odonata)[END_REF]. Because of the notorious incongruence between morphological and molecular evidence in phylogenetic reconstructions it was even suggested to refrain from using morphological data at all (e.g., [START_REF] Scotland | Phylogeny reconstruction: the role of morphology[END_REF], which is of course impossible with fossil taxa [START_REF] Wiens | The role of morphological data in phylogeny reconstruction[END_REF]. [START_REF] Pongrácz | Die eozäne Insektenfauna des Geiseltales[END_REF] described Eothaumatoneura from the Eocene of Germany and attributed it to Thaumatoneuridae, but [START_REF] Nel | Les Lestoidea (Odonata, Zygoptera) fossiles: un inventaire critique[END_REF] transferred it to Zygoptera incertae sedis. [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF] attributed the mostly Paleogene Dysagrioninae [START_REF] Cockerell | [END_REF](Petrolestes, Congqingia, Dysagrion Scudder, 1878, and Phenacolestes Cockerell, 1908) and Early Cretaceous Euarchistigmatinae [START_REF] Carle | Early Cretaceous, Crato, Brazil) E. marialuiseae Bechly[END_REF] to Thaumatoneuridae within Amphipterygoidea. [START_REF] Petrulevičius | A new damselfly family from the Upper Palaeocene of Argentina[END_REF] considered the Paleogene Latibasalia as possibly related to Dysagrioninae within Amphipterygoidea, but we here transferred this taxon to Epallagoidea (see above). [START_REF] Nel | New fossil Odonata from the European Cenozoic (Insecta: Odonata: Thaumatoneuridae, Aeshnidae, Idionychidae, Libellulidae)[END_REF] described Primorilestes from the Eocene of Russia. [START_REF] Nel | The first Baltic amber dysagrionine damselfly (Odonata: Zygoptera: Thaumatoneuridae: Dysagrioninae)[END_REF] added Electrophenacolestes from Eocene Baltic amber to Dysagrioninae, and [START_REF] Rust | The first damselflies from the Lowermost Eocene of Denmark, with a description of a new subfamily (Odonata, Zygoptera: Dysagrionidae)[END_REF] added Eodysagrion in a separate subfamily Eodysagrioninae (and synonymized Thaumatoneuridae with Dysagrionidae). [START_REF] Nel | Dragonflies and damselflies (Insecta: Odonata) from the Late Eocene of the Isle of Wight[END_REF] described an unnamed dysagrionine from the Eocene-Oligocene of the Isle of Wight. Finally, Zheng et al. (2016cZheng et al. ( , 2016d) ) described Palaeodysagrion and Burmadysagrion, both from Burmite. These fossil taxa are discussed below and their phylogenetic position is revised. [START_REF] Pongrácz | Die eozäne Insektenfauna des Geiseltales[END_REF] is a fossil damselfly that is only known from wing fragments of a single specimen from the Middle Eocene (Middle Lutetian, MP13, 44.3 Ma) Geiseltal locality in eastern Germany. [START_REF] Nel | Les Lestoidea (Odonata, Zygoptera) fossiles: un inventaire critique[END_REF] considered that this material as too incompletely preserved to be accurately placed, and therefore transferred this taxon from Thaumatoneuridae to Zygoptera incertae sedis. Nevertheless, the preserved parts of the wing venation of Eothaumatoneura are very similar to the corresponding structures in the extant Neotropical damselfly genus Thaumatoneura, especially in the very long postnodal area, base of RP2 far removed from subnodus, absence of lestine oblique vein 'O', main veins strongly curved posteriorly, presence of 2-3 secondary longitudinal veins in distal part of postdiscoidal area between MA and MP, presence of 4-5 secondary longitudinal veins in distal part of area between MP and CuA, cubital area certainly broad, even if poorly preserved (see Pongrácz, 1935: figs. 11-14). This pattern of venation is not shared by any of the known Paleogene damselfly-like Odonata with large wings (e.g., Sieblosiidae, Dysagrionidae, or even the damsel-dragonfly family Pseudostenolestidae from the Eocene of Messel, [START_REF] Garrouste | New Eocene damselflies and first Cenozoic damsel-dragonfly of the isophlebiopteran lineage (Insecta: Odonata)[END_REF]. Consequently, there are no arguments against an attribution of Eothaumatoneura ptychoptera to Thaumatoneuridae, which is suggested by the above mentioned wing venational similarities. Therefore, we here propose to restore this fossil taxon in Thaumatoneuridae. Eothaumatoneura seems to be more closely related to the extant genus Thaumatoneura than to the other extant thaumatoneurid genus Paraphlebia, because the wing venation is much more similar to the former genus in several derived character states. [START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF][START_REF] Bechly | Odonata: damselflies and dragonflies[END_REF]Bechly ( , 2010) ) attributed Euarchistigma from the Lower Cretaceous Crato Formation of Brazil to the Thaumatoneuridae (Euarchistigmatini) rather than to the Pseudostigmatinae (as originally proposed by [START_REF] Carle | Odonata[END_REF], on the basis of the following putative synapomorphies: antesubnodal space without any crossveins; nodus and bases of IR2 and RP3/4 shifted to an extremely basal position, correlated with a large number of postnodal crossveins; IR2 apparently arising on RP3/4; very dense wing venation with a high number of cells; dark colour pattern of wings; longitudinal wing veins distally distinctly curved to the posterior wing margin. All these characters are also present in at least some modern Pseudostigmatinae, but do mostly not belong to the ground plan of this family. Even though the position of Euarchistigma remains somewhat unclear, we here tentatively retain it in Thaumatoneuridae as Euarchistigmatinae stat rest. Mesomegaloprepus differs from Euarchistigma in the presence of three secondary antenodal crossveins, presence of several rows of cells in cubital area, intercalary veins present between main longitudinal veins, triadic branching pattern of CuA and MP [START_REF] Bechly | Odonata: damselflies and dragonflies[END_REF](Bechly, , 2010)).

Status of alleged fossil Thaumatoneuridae

Eothaumatoneura ptychoptera

The Dysagrioninae are an extinct Cenozoic damselfly group, with the sole exception of Congqingia from the Cretaceous of China. The placement of the Dysagrioninae (Dysagrionini Cockerell, 1908 andPetrolestini Cockerell, 1927) within the Thaumatoneuridae, as proposed by [START_REF] Bechly | Morphologische Untersuchungen am Flügelgeäder der rezenten Libellen und deren Stammgruppenvertreter (Insecta; Pterygota; Odonata), unter besonderer Berücksichtigung der Phylogenetischen Systematik und des Grundplanes der Odonata[END_REF][START_REF] Bechly | Phylogenetic Systematics of Odonata[END_REF] and [START_REF] Rust | The first damselflies from the Lowermost Eocene of Denmark, with a description of a new subfamily (Odonata, Zygoptera: Dysagrionidae)[END_REF] is only supported by two very weak alleged synapomorphies: basal costal margin between wing base and nodus is distinctly convex curved; antesubnodal space without any crossveins. The first character is probably correlated to the shortening the antenodal space and could have been convergently acquired. The second character is present in several unrelated clades, and thus very homoplastic, as already indicated above. Since the affinities of the Dysagrioninae are uncertain, we prefer to exclude these damselflies from the Thaumatoneuridae and suggest to restate the Dysagrionini and Petrolestini as subfamilies to a separate family Dysagrionidae stat. rest., as already suggested by [START_REF] Garrouste | New Eocene damselflies and first Cenozoic damsel-dragonfly of the isophlebiopteran lineage (Insecta: Odonata)[END_REF] and Zheng et al. (2016d). Our rejection of the synonymy of Thaumatoneuridae with Dysagrionidae (contra [START_REF] Rust | The first damselflies from the Lowermost Eocene of Denmark, with a description of a new subfamily (Odonata, Zygoptera: Dysagrionidae)[END_REF] implies that Thaumatoneuridae is restored as valid family as well. The Dysagrioninae are characterized by a potential synapomorphy, viz a rather unique shape of the discoidal cell with a distal side distinctly longer than its basal side and anterior and posterior sides not parallel, even if it is also present in the Cenozoic Sieblosiidae. Mesomegaloprepus does not share the above mentioned two potential synapomorphies of Dysagrioninae and Thaumatoneuridae, and also lacks the typical dysagrionine shape of the discoidal cell.

Eodysagrion [START_REF] Rust | The first damselflies from the Lowermost Eocene of Denmark, with a description of a new subfamily (Odonata, Zygoptera: Dysagrionidae)[END_REF] from the Paleogene of Denmark was placed in a separate subfamily Eodysagrioninae within Dysagrionidae [START_REF] Rust | The first damselflies from the Lowermost Eocene of Denmark, with a description of a new subfamily (Odonata, Zygoptera: Dysagrionidae)[END_REF]. Eodysagrion shares two apomorphies with the Thaumatoneurinae: discoidal cell perfectly rectangular; and IR2 apparently arising on RP3⁄4. Also, in Eodysagrion, the broadening of the antenodal area, typical of Thaumatoneura, is weakly indicated, and the dark banded colour pattern of the wings may correspond as well. However, Eodysagrion differs markedly from Thaumatoneura in its clearly less numerous secondary longitudinal veins, its nodus not in a very basal position, less numerous postdiscoidal crossveins, and its longitudinal wing veins not distinctly curved distal to the posterior wing margin. Note that the Eodysagrion and Euarchistigma do not have the discoidal cell of 'sieblosiid' type as in Dysagrioninae. Nevertheless, we provisionally maintain Eodysagrion in the Thaumatoneuridae. Mesomegaloprepus differs from Eodysagrion in the presence of three secondary antenodal crossveins, and a different pattern of veins in the cubital area [START_REF] Rust | The first damselflies from the Lowermost Eocene of Denmark, with a description of a new subfamily (Odonata, Zygoptera: Dysagrionidae)[END_REF].

Palaeobiogeography and Palaeoecology

Even though the evidence for phylogenetic relationships of Mesomegaloprepidae still is ambiguous, the three most likely candidates for sister group are all Neotropical taxa.

Together with an unequivocal fossil Thaumatoneuridae from the Eocene of Europe, our new discovery may suggest a great antiquity and wide past distribution for at least some of these Neotropical damselfly groups.

The fact that we have the surprising number of six pieces of Burmite amber with totally 11 conspecific specimens (three pieces contain both sexes) of this new damselfly taxon strongly suggests that it was a rather abundant element of the Myanmar amber forest. Most probably these insects oviposited like modern Pseudostigmatinae in phytotelmata on the amber tree, and also mated there, because this would have greatly increased the likelihood of getting trapped in tree resin, and therefore could explain the relatively large number of inclusions. This could even be a further hint towards a pseudostigmatine relationship of Mesomegaloprepidae, because recent males of Pseudostigmatinae defend large water-filled tree holes as breeding territories, where they mate with multiple females that oviposit in the tree hole, where the cannibalistic larvae develop [START_REF] Fincke | Giant damselflies in a tropical forest: reproductive biology of Megaloprepus coerulatus with notes on Mecistogaster (Zygoptera: Pseudostigmatidae)[END_REF](Fincke, , 1992a(Fincke, , 1992b[START_REF] Fincke | Larval behaviour of a giant damselfly: territoriality or size-dependent dominance?[END_REF][START_REF] Fincke | Use of forest and tree species, and dispersal by giant damselflies (Pseudostigmatidae): their prospects in fragmented forests[END_REF].

Concluding remarks

This fossil damselfly represents a new family, genus, and species from mid-Cretaceous amber from Myanmar, with ambiguous phylogenetic relationships to modern Neotropical taxa. It adds to our knowledge of the diverse entomofauna of Burmese amber, and to our knowledge of Mesozoic damselflies and their palaeobiogeographic distribution.

Figures legends

  Figs.2-8

  shows several similarities with Latibasaliidae: arculus distinctly basal of Ax2; Ax1 and Ax2 close together; very oblique nodal and subnodal veinlets; postnodal crossveins not aligned with postsubnodal crossveins (symplesiomorphy); pterostigmal brace reduced; midfork (origins of IR2 and RP3/4) recessed distinctly basal of subnodus; discoidal cell quadrangular; distal side MAb of discoidal cell with reversed obliquity; cubital space expanded with several rows of cells; longitudinal veins distally strongly curved; secondary intercalary branches between RP3/4 and MA, and between MA and MP; no lestine oblique vein 'O'; wings with dark banded colour pattern. However, Mesomegaloprepus differs from Latibasaliidae in several important characters: nodus in more basal position; midfork mid way between arculus and subnodus (instead of being recessed much closer to arculus); basal side of pterostigma not oblique; triadic branchings of CuA. Further potential differences (viz. secondary antenodals between C and ScP distal of Ax2, several antesubnodal crossveins, and subdiscoidal cell divided) are not totally certain, because the corresponding wing areas seem not very well preserved in the known specimens of Latibasaliidae.

  : Coryphagrionini (only including Coryphagrion as sister group to Neotropical pseudostigmatines), Pseudostigmatini (including the two narrow-winged genera Mecistogaster and Pseudostigma Selys, 1860 with simple longitudinal veins), and Megaloprepini (broad-winged genera Microstigma Rambur, 1842, Anomisma McLachlan, 1877, and Megaloprepus , with characteristic triadic branchings of longitudinal veins MA and CuA). The phylogeny and

  (Pseudostigmatinae: Megaloprepini) are as follows: discoidal cell not very acute (contrary to other Pseudostigmatinae); longitudinal wing veins being distally distinctly curved to the posterior wing margin (also present in Thaumatoneura); more strongly developed triadic branching pattern of distal part of MP; dark banded colour pattern of wings with sexual dimorphism (as in Thaumatoneura). The absence of intercalary veins between MP and CuA (symplesiomorphy), and the presence of secondary longitudinal veins in area between MP and MA apparently emerging from MP (thus possibly a precursor of the triadic branching of MP in Megaloprepus) are characters that would rather support an attribution of Mesomegaloprepus to Pseudostigmatinae close to Megaloprepus (MP is apically shortly forked in Anomisma and Microstigma, but simple in Coryphagrion, Mecistogaster, and Pseudostigma). Altogether, the wing venational similarities with Pseudostigmatinae are either very weak characters (pterostigma short and stigmal brace reduced) or clearly convergences (similarities with Megaloprepus), because a subordinate ingroup position of Mesomegaloprepus within Pseudostigmatinae is excluded by its plesiomorphic absence of several derived groundplan characters of Pseudostigmatinae and Megaloprepini (see above), while the similarities between Mesomegaloprepus and broad-winged Megaloprepini do not belong to the ground plan of Pseudostigmatinae as documented by the very similar wing venations of the most basal pseudostigmatine genera Coryphagrion, Mecistogaster, and Pseudostigma. The characteristical ligula with single terminal flagellum is a derived similarity of Mesomegaloprepus with Neotropical Pseudostigmatini + Megaloprepini, but it is still absent in Coryphagrionini, and is homoplastic in recent damselflies (e.g., present in the unrelated agriolestid genus Podopteryx Selys, 1871 according to

Figure 1 :

 1 Figure 1: Mesomegaloprepus magnificus gen. et sp. nov., habitus. a-Holotype, female, NIGP

Figure 2 :

 2 Figure 2: Mesomegaloprepus magnificus gen. et sp. nov., habitus. a-Paratypes, several males

Figure 3 :

 3 Figure 3: Mesomegaloprepus magnificus gen. et sp. nov., head. a-Photograph of head of

Figure 4 :

 4 Figure 4: Mesomegaloprepus magnificus gen. et sp. nov., photograph of wings of holotype,

Figure 5 :

 5 Figure 5: Mesomegaloprepus magnificus gen. et sp. nov., drawing of wings of holotype,

Figure 6 :

 6 Figure 6: Mesomegaloprepus magnificus gen. et sp. nov., drawing of wings. a-Forewing of

Figure 7 :

 7 Figure 7: Mesomegaloprepus magnificus gen. et sp. nov., male terminalia; paratype NIGP

Figure 8 :

 8 Figure 8: Mesomegaloprepus magnificus gen. et sp. nov., male genitalia on second abdominal

Acknowledgments

GB thanks Sieghard Ellenberger (Kassel, Germany) for providing the paratype Bu-231 to SMNS and for macro-photos of this specimen. HDY is grateful to National Basic Research Program of China (2012CB821903), Outstanding Youth Foundation of Jiangsu Province (BK 2012049), and the National Natural Science Foundation of China (91114201) for supporting funds. DA wants to thank the Chinese Academy of Sciences for the financial support under the CAS President's International Fellowship Initiative (PIFI). This paper is a contribution of the team project "Biodiversity: Origin, Structure, Evolution and Geology" and to the activity of the laboratory "Advanced Micropalaeontology, Biodiversity and Evolution Researches (AMBER)" led by Dany Azar at the Lebanese University.

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