A Late Jurassic-?earliest Cretaceous ctenochasmatid (Pterosauria, Pterodactyloidea): The first report of pterosaurs from Uruguay

Journal of South American Earth Sciences 85 (2018) 298–306

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A Late Jurassic-?earliest Cretaceous ctenochasmatid (Pterosauria, Pterodactyloidea): The first report of pterosaurs from Uruguay

T

Daniel Pereaa, Matías Sotoa,∗, Pablo Toriñoa, Valeria Mesaa, John G. Maiseyb a b

Instituto de Ciencias Geológicas, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay Division of Paleontology, American Museum of Natural History, Central Park West, 79th Street, NY 10024-5192, USA

A R T I C LE I N FO

A B S T R A C T

Keywords: Ctenochasmatidae Late Jurassic South America Gondwana

The Tacuarembó Formation contains a faunal assemblage with some taxa clearly indicative of a Late JurassicEarly Cretaceous age. In this context, the first remains of Uruguayan pterosaurs are described. These correspond to a dorsoventrally compressed and narrow fragment of a rostrum widening anteriorly, with alveoli and a very fragmentary dentition including a tooth base. The orientation of the alveoli and preserved tooth base allows the assumption that the teeth were projected laterally and forward from the dental borders. The deep interdental concavities make up a wavy contour of the lateral margins of the rostrum. Both morphology and size correspond to that observed in the ctenochasmatid gnathosaurines. The Uruguayan pterosaur remains represent the oldest ctenochasmatid found in South America and suggest an age of the fossiliferous horizon no older than Late Jurassic, which was already established on the basis of other fossils, such as Priohybodus arambourgui d'Erasmo, 1960.

1. Introduction

2. Material and methods

During the last two decades the knowledge of the vertebrate assemblage of the Tacuarembó Formation has significantly increased (Perea et al., 2001, 2003; 2009, 2014; Soto and Perea, 2008, 2010; Soto et al., 2012a; b; Mesa and Perea, 2015). Here we describe and analyze the first remains of pterosaurs ever found in Uruguay. The studied material, the fragment of anterior part of a rostrum, was originally classified erroneously as a probable sawfish (Perea et al., 2016). However, more detailed studies by high resolution computed tomography, refuted that hypothesis. Pterosaurs were the first vertebrate group that conquered the skies. In South America, pterosaurs are known from spectacular findings, such as those from the Early Cretaceous Santana Group (Neumann and Cabrera, 1999), where a variety of exceptionally preserved crested forms, belonging to different taxa, were found (Maisey, 1991; Kellner and Tomida, 2000). However, Jurassic pterosaurs from this continent are poorly known. They include forms from the lacustrine Cañadón Asfalto Formation (Middle Jurassic of Patagonia, Codorniú et al., 2016) and the marine Vaca Muerta Formation (Late Jurassic of Patagonia, Casamiquela, 1975, Codorniú and Gasparini, 2013). Herein we report a valuable addition to the Jurassic record of South American pterosaurs.

Regular and frequent fieldwork was undertaken at the diverse outcrops of the Tacuarembó Formation in northern Uruguay in order to collect fossil material and observe the stratigraphic distribution of the fauna of this unit. A new locality, situated about 2 km northwest of Batoví Hill (close to Batoví Quarry and the homonimous locality mentioned by Soto et al., 2012b), is reported here for the first time. This locality has yielded the rostrum fragment described below. In order to collect the here described rostrum fragment it was necessary to use electro pneumatic hammer, because of the hardness of the sandstone. In the laboratory, mechanical preparation techniques were used under binocular magnifying glasses. To reinforce the specimen, cyanoacrylate consolidating agents were used. The detailed anatomical study of the material had to be complemented necessarily with conventional and high resolution computerized tomography (micro-CT). A preliminar CT scan of the studied rostrum fragment was performed in a Siemens Somaton Sensation 64 CT scanner device, at Unidad de Radiología - Hospital de Clínicas, Universidad de la República (Uruguay). The specimen was scanned in the coronal plane with a voltage of 100 KV and a current of 155 mA, with a resolution of

∗

Corresponding author. E-mail addresses: [email protected] (D. Perea), [email protected] (M. Soto), [email protected] (P. Toriño), [email protected] (V. Mesa), [email protected] (J.G. Maisey). https://doi.org/10.1016/j.jsames.2018.05.011 Received 2 February 2018; Received in revised form 14 May 2018; Accepted 16 May 2018 Available online 18 May 2018 0895-9811/ © 2018 Elsevier Ltd. All rights reserved.

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members of which are unique to this unit, including the bivalve Tacuaremboia caorsi Martínez et al., 1993, the crocodyliform Meridiosaurus vallisparadisi Mones, 1980, and the turtle Tacuarembemys kusterae Perea et al., 2014. Other taxa are more widespread, with occurences in other units of Western Gondwana, such as the shark Priohybodus arambourgi d'Erasmo, 1960, the lungfish Arganodus tiguidiensis (Martin, 1982), and the coelacanth Mawsonia Woodward in Mawson and Woodward (1907) (see Perea et al., 2001; Soto and Perea, 2010; Soto et al., 2012a; b). Most of the taxa with a wider geographic distribution indicate a chronological interval spanning the Late JurassicEarly Cretaceous (e.g. Perea et al., 2009; see below). This is corroborated by radiometric dates from overlying basalts, indicating that the Tacuarembó Formation cannot be younger than the Hauterivian (Perea et al., 2001, 2009, and references therein). Dinosaurs are the only strictly terrestrial members of this faunal assemblage. They are represented by shed theropod teeth (Perea et al., 2003, 2009; Soto and Perea, 2008), and ichnites of sauropods, theropods and ornithopods (Mesa and Perea, 2015). The vertebrate assemblage of the Tacuarembó Formation mostly consists of aquatic or amphibian animals, which clearly depended on the ephemeral and perennial fluvial systems in which the fossiliferous sediments of this unit, were deposited. In the semi-arid conditions, under which the Batoví Member Formation supposedly formed (Perea et al., 2009), the dinosaurs would have also depended substantially on these water bodies. The rostral fragment described herein was found in a 2.5-m thick yellowish, fine grained sandstone (Fig. 2). The sandstone starts with a basal horizon of pelitic intraclasts, and is massive, showing low-angle cross-bedding towards the top. Overall, this sedimentary log (Fig. 2A) is indicative of an ephemeral river, characterized by episodes of higher and lower discharge. The pterosaur rostrum fragment was found spatially associated with etched ganoid scales and unidentified bone fragments in a patchy bonebed (Fig. 2C). Fossil preservation is poor compared to other Tacuarembó Formation bonebed material, such as those from the localities of Martinote, Los Rosanos and Bidegain Quarry from where the isolated teeth here described came (e.g. Perea et al., 2001, 2003; 2009; Soto et al., 2012b). The taphonomy of the remains described here indicates a probable transport away from the original habitat of the living organisms, in particular the rostral fragment showing a high degree of wear, which is herein interpreted as a parautochthonous component of the assemblage.

Fig. 1. Map showing pterosaurian fossil localities (black squares) for the Tacuarembó Formation discussed in the text. 1, FC-DPV-2869, rostral fragment. 2, FC-DPV-3090, isolated teeth.

0,6 mm. With the aim to obtain higher resolution images, a second scan was performed in a General Electric Phoenix x-ray micro CT scanner device, at Laboratório Multiusuário de Processamento de Imagens de Microtomografia Computadorizada de Alta Resolução - Museu de Zoologia da Universidade de São Paulo (Brazil). In this last case the specimen was scanned with a tube voltage of 90 KV and a tube current of 265 μA, with a resolution of 0,02 mm in the three axes. Taxonomy follows Witton (2013) and Andres et al. (2014). Stratigraphic nomenclature follows Perea et al. (2009). Institutional abbreviations: FC-DPV, Vertebrate Fossil Collection, Facultad de Ciencias, UdelaR, Montevideo, Uruguay.

4. Systematic Paleontology PTEROSAURIA Kaup, 1834. PTERODACTYLOIDEA Plieninger, 1901. CTENOCHASMATIDAE Nopsca, 1928. GNATHOSAURINAE Unwin, 1992. GNATHOSAURINAE gen. et sp. indet. Figs. 3, 4, 5.

3. Geological setting, age, and taphonomy The sandstones that form the Tacuarembó Formation (Bossi, 1966), which crops out in the northern region of Uruguay (Fig. 1), are divided into two members (Bossi et al., 1975), later named Batoví (lower) and Rivera (upper) members, respectively (Perea et al., 2009). Most of the thickness of the unit is formed by the Batoví Member, which is so far the only fossiliferous one. Intensive field work carried out in this member yielded abundant fossils of bivalves, gastropods, conchostracans, hybodontid sharks, ginglymodians, actinistians, dipnoans, crocodyliforms, and theropod dinosaurs (see Perea et al., 2009). Moreover, ichnofossils attributed to sauropod, theropod and ornithopod dinosaurs have been recently described (Mesa and Perea, 2015). The Tacuarembó Formation has a peculiar fossil assemblage, some

4.1. Material FC-DPV-2869, fragment from the anterior part of a maxillopremaxillary rostrum with 18 alveoli (Fig. 3), including the root of one tooth (Fig. 4).

4.2. Locality and horizon The specimen comes from near the Batoví Quarry, Tacuarembó province, northern Uruguay (Figs. 1 and 2; see Geological Setting above), Batoví Member, Late Jurassic-?earliest Cretaceous of the Tacuarembó Formation. 299

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Fig. 2. Stratigraphic location of FC-DPV-2869 rostral fragment and sedimentological log. A-B, general views of the outcrop. C, detail of bone-bed showing ganoid scales. D, sedimentological log.

condition in Pristidae (see Fig. 3c in Underwood et al., 2015). The alveoli are ovoid (Fig. 3B, D) and have an average width of 2.4 mm labiolingually and 3.2 mm anteroposteriorly. Their sockets are deep (6 mm average depth; Fig. 3C). Alveoli from the left and right sides are very close to each other in the midline of the rostrum (approximately 1.5 mm apart from each other; Fig. 3C). The alveolar rims are arranged between deep concavities of the rostrum borders, giving the margin a conspicuous wavy outline in both dorsal (Fig. 3A) and ventral views. In lateral view the alveoli are slightly closer to the ventral plane than to the dorsal one (Fig. 3B). Micro-CT also revealed that the piece is hollow, retaining mainly the outer compact bone, a tooth root (Fig. 4) and a thin inner bone wall in some alveoli (Fig. 3C and D). No premaxillary sagittal crest is present in the preserved fragment.

4.3. Description The specimen (Fig. 3) is approx. 64 mm long and about 12 mm narrow; it is flattened but it seems not by overburden, have a smooth texture, and lacks crests or grooves in its dorsal (Fig. 3A) and ventral surfaces. It shows a slight concavity in the latter surface (Fig. 3B), but it is difficult to know if this concavity is real or an artifact. It is slightly more expanded anteriorly than posteriorly (12.48 mm anterior width vs 11.06 mm posterior width), suggesting some kind of spatula was developed anteriorly (Fig. 3A). Unfortunately, it is not possible to assess the shape and degree of development of the spatula. FC-DPV-2869 is dorsoventrally depressed (maximum thickness 5.2 mm anteriorly and 6.1 mm posteriorly; Fig. 3B). The outer bone surface is compact, very fractured, and it is not possible to observe sutures between bones (Fig. 3A). Ten out of 18 alveoli are present, nine on each side, but five on each side are the best preserved of them (Fig. 3). The sandstone filling each alveolus protrudes perpendicular from the apperture. This may be due to the partial formation of an imperfect sandstone mold of each tooth. The sediment filling the alveoli is the same that characterizes the Batoví Member of the Tacuarembó Formation. The referred protruding perpendicularly sandstone molds (Fig. 3A) initially led the previous researchers to think they were tooth casts and thus interpreted the specimen as a sawfish rostrum. However, examination with micro-CT revealed that the alveoli as well as the single preserved tooth root (Fig. 4) were in fact obliquely orientated about 45° from de longitudinal axis, pointing anterolaterally from the dental border (Fig. 3C) and not perpendicularly arranged, 90° from the longitudinal axis, as is the

4.4. Comparison The specimen FC-DPV-2869 shows diagnostic characters that allows referring it to the family Ctenochasmatidae, such as a narrow and dorsoventrally compressed rostrum with the teeth anterolaterally directed and inserted laterally in the jaw margins (see Wellnhofer, 1970, 1978; Unwin, 2003; Kellner, 2003). The specimen size is approximately similar to that of Gnathosaurus Meyer, 1834, and smaller than Huanhepterus Dong, 1982, Plataleorhynchus Howse and Millner, 1995, and Forfexopterus Jiang et al., 2016. The wavy margin of the rostrum fragment is similar to those of Gnathosaurus and Plataleorhynchus. The tooth density in the preserved 300

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Fig. 3. Conventional photographs of FC-DPV-2869 in dorsal (A) and right lateral views (B) (arrow indicates the slight ventral concavity referred in text). Micro CT photographs of FC-DPV-2869 in dorsal (C) and right lateral views (D). The square indicates the single preserved tooth root (see Fig. 4). In all cases, anterior is to the right of the picture. Scale bar: 1 cm.

skull and mandible remains from the Solnhofen Limestone of Germany and G. macrurus (Seeley, 1869) Howse and Millner, 1995 on a mandible from the Purbeck Limestone of England. The lack of a premaxillary sagittal crest is present makes FC-DPV2869 different from Huanhepterus, Gegepterus and moganopterines (Dong, 1982; Wang et al., 2007). Because of its fragmentary nature, the specimen FC-DPV-2869 lacks distinctive characters that would allow a trustworthy assignment beyond Gnathosaurinae, but the character combination suggest it may be a new genus and species (Table 1). However, the discovery of more complete material is needed before reaching such a conclusion.

fragment is 1.4 teeth/10 mm, similar to Huanhepterus and Forfexopterus but much lower than other ctenochasmatids with tightly packed teeth like Ctenochasma Meyer, 1852, Pterofiltrus Jiang and Wang, 2011, Cathayopterus Wang and Zhou, 2006, and Gegepterus Wang et al., 2007, among others (see Table 1). The specimen shows similarities with Gnathosaurus and Platalaeorhynchus, particularly the wavy margins and the expansion of the anterior terminus of the rostrum (spatula). The spatula is rather ovoid and confluent with the posterior part of the rostrum in Gnathosaurus and circular and demarcated from the remainder of the rostrum in Platalaeorhynchus (Howse and Millner, 1995), but the original shape and degree of development of this expansion cannot be assessed in FC-DPV-2869. The similar size and the smooth surface on the palatinal surface in the new specimen nevertheless may suggest greater similarity with Gnathosaurus than Platalaeorhynchus. Huanhepterus (the sister taxon to Plataleorhynchus + Gnathosaurus; Andres et al., 2014) also has a terminal expansion of the rostrum, although it is bigger, less dorsoventrally depressed, and possess a dorsal crest that almost reaches the anterior terminus of the rostrum (Jiang et al., 2016). Other ctenochasmatids, such as Forfexopterus and Ctenochasma, lack an expansion of the anterior part of the rostrum. Among Gnathosaurus species, G. subulatus Meyer, 1834 is based on

?GNATHOSAURINAE gen. et sp. indet. Fig. 6 4.5. Material FC-DPV 3090, six isolated teeth. 4.6. Locality and horizon Bidegain Quarry, a few kilometers northeast of Batoví Quarry 301

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Fig. 4. Micro CT photographs of tooth included in rostral fragment in dorsal view (FC-DPV-2869); and cross sections through three levels: apex of the root (A), the base of the crown (C) and an intermediate level (B). Scale bars: 1 mm.

Fig. 5. Schematic drawing showing the probable anatomical position of the rostral fragment FC-DPV-2869 in a reconstructed Gnathosaurus skull. A, dorsal view. B, right lateral view. Redrawn from Wellnhofer (1991). Scale: 10 cm. 302

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Yes

No

No

No

Yes

Yes (posteriorly placed in Gnathosaurus)

No (at least anteriorly)

Yes

4.8. Comparison

No

No

Most teeth not set in alveoly but in a longitudinal groove In alveoli which are placed in a longitudinal groove

Ctenochasmatid teeth are always described as long, slender and curved, the upper teeth of the aberrant Pterodaustro Bonaparte, 1970 being the exception. The Uruguayan teeth show the above mentioned characters. Size and spacing of ctenochasmatid teeth tend to decrease and increase distally, respectively. Orientation can also vary, with anteriormost teeth splaying anterolaterally and the remainder of the dentition pointing laterally (e.g. Howse and Millner, 1995). Slenderness can vary among different species of a genus, as is the case in Ctenochasma (Bennett, 2007). The presence of an enamel cap is a feature typical of all toothed pterosaurs (Witton, 2013). The size and morphology of the tooth figured herein are consistent with the rostrum fragment FCDPV-2869 (compare Figs. 4C and 6D). Hence, we propose ctenochasmatid origins for the teeth FC-DPV 3090.

5.3 (6.0 anteriorly)

NA

Most teeth are less than 10 mm tall, curved (Fig. 6C), and considerably more slender than other tetrapod teeth from the unit (see Soto and Perea, 2008; Perea et al., 2009; Soto, 2016). Basal cross-section is subcircular to elyptical (Fig. 6E), with a crown base ratio close to 0.80. The pulp cavity is small. Two of the teeth lack enamel, and given the resistance of tooth enamel to transport induced-abrasion (e.g. Argast et al., 1987) we interpret them as swallowed teeth rather than simply being completely worn down as a result of transport. In the remaining teeth enamel is smooth to the naked eye. At least in the tooth figured herein (which is a broken, rather than shed teeth), enamel is restricted to an apical cap which covers about half the preserved tooth portion. One tooth has at least two well marked apicobasal ridges. Denticles are not observed in any of the teeth. Some of the teeth show apical wear.

Not reported nor appreciated

Yes (strongly)

Yes

Not reported nor appreciated No No

Only in smaller specimens In alveoli 2.9 in C. roemeri 4.6 in C. taqueti 7.4 in C. elegans

In alveoli

Not reported nor appreciated Not reported nor appreciated Yes 0.7 in Moganopterus

1.6 Huanhepterus 2.4 G. macrurus* 2.9 Plataleorhynchus*

Yes

Only in Huanhepterus Yes No

Yes

No Yes NA

In alveoli, with alveolar rims formed from short raised collars of bone In alveoli, with alveolar rims formed from short raised collars of bone in Plataleorhynchus. In alveoli 1.4

4.9*

Premaxillary sagittal crest Concave dorsal margin Crenellated rostrum margin in dorsal/ ventral view

4.7. Description

Teeth restricted to anterior third of skull and mandible Tooth placement Tooth density (teeth per 10 mm)

(Fig. 1) (see also Soto et al., 2012b); in 1 m thick fossiliferous deposit, spatially associated with dispersed ganoid scales, complete bones of mawsoniid coelacants, isolated dipnoans toothplates and theropod dinosaur teeth; Batoví Member, Late Jurassic-?earliest Cretaceous of the Tacuarembó Formation.

5. Discussion and conclusions

150

> 1000

The oldest ctenochasmatoid pterosaur remains come from the Oxfordian of China (Laiodactylus Zhou et al., 2017). The family was diversified and geographically extended by the latest Jurassic, including Gnathosaurus and Aurorazhdarcho Frey et al., 2011 from the Solnhofen Limestone of Germany, Ctenochasma from the “Purbeck” of Germany and the Calcaires tâchetés of France, and possibly Kepodactylus Harris and Carpenter, 1996 from the Morrison Formation (Fig. 7A). From the Jurassic-Cretaceous transition Plataleorhynchus and another Gnathosaurus species from the Purbeck Limestone of England were reported (Howse and Millner, 1995, Fig. 7A). In the Early Cretaceous (Fig. 7B) several genera from the Liaoning and Jiufotang formations of China were described (e.g. Dong, 1982; Wang and Zhou, 2006; Wang et al., 2007; Jiang and Wang, 2011; Jiang et al., 2016), as well as the South American representatives of the family: an indeterminate gnathosaurine from the Quebrada Monardes Formation (Martill et al., 2006), and Pterodaustro from the Lagarcito Formation of Argentina, the youngest member of the clade (i.e. Albian). The occurrence of a ctenochasmatid pterosaur in the Tacuarembó Formation is another strong evidence favouring an age not older than Late Jurassic for the fossiliferous horizon (contra Bossi and Ferrando, 2001), as already suggested by the presence of the conchostracan Orthestheria (Migransia) (Chen & Shen) Shen, 2003, the shark Priohybodus arambourgi, the coelacanth Mawsonia and ceratosaurid and megalosaurid theropods (Perea et al., 2001; Shen et al., 2004; Soto and

No

No

No

Liaodactylus

Pterodaustro

Gegepterus

Strongly elongated (85%) Elongated (69%)

152

No Ctenochasma

Elongated (64%, lower in smaller specimens) Elongated (49.1%)

64 in Moganopterus 76 in Feilongus 200-552 (lower in smaller specimens) No Moganopterinae

Elongated (67%)

128-136 Gnathosaurus 144–152 Plataleorhynchus 100–108 Huanhepterus Yes Gnathosaurinae

Elongated (54% in Gnathosaurus)

NA NA Yes (inferred) Uruguayan material

Rostrum elongation

Tooth number

5.1. Chronostratigraphical and paleobiogeographical implications

Spatula

Table 1 Comparison of selected cranial and dental features among several ctenochasmatid taxa. Data taken or measured (*) from several sources (e.g. Dong, 1982; Howse and Millner, 1995; Wang and Zhou, 2006; Bennett, 2007; Wang et al., 2007; Jiang and Wang, 2011; Andres et al., 2014; Jiang et al., 2016; Zhou et al., 2017).

D. Perea et al.

303

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Fig. 6. Isolated tooth included in FC-DPV-3090. A, mesial view. B, distal view. C, dorsal/ventral view. D, detail of the square included in C, showing enamel cap. E, basal view. Scale bars: 0.5 cm (A–C) and 0.25 cm (D).

like conchostracans, and diverse fishes, are known for the Batoví Member. Although the taphonomy may indicate an important degree of transport of the studied material it undoubtedly belongs to the Tacuarembó Formation, which expands the characteristics of the aquatic systems linked to this unit, including shallow lazy water environments related to the wading habits postulated for ctenochasmatids (Wellnhofer, 1991; Witton, 2013). Almost all Late Jurassic ctenochasmatids have been found in marine environments (Andres et al., 2014), thus making the Uruguayan specimen one of the few continental ctenochasmatids from that epoch. Conversely, most Early Cretaceous forms were continental rather than marine (Andres et al., 2014). The finding of a pterosaur in the Tacuarembó Formation, confirms that the diversity of the vertebrate assemblage, and thus the complexity of the tetrapod components of food webs, was greater than expected, as already suggested based on dinosaur tracks (Mesa and Perea, 2015) and theropod teeth (Perea et al., 2003; Soto and Perea, 2008; Soto, 2016).

Perea, 2008; Soto et al., 2012a, 2012b, 2016). Moreover, nor ceratosaurids with grooved rostral teeth neither megalosaurids are found in Early Cretaceous units (Soto and Perea, 2008; Soto, 2016); and the conchostracan from Uruguay is more alike Late Jurassic than Early Cretaceous forms (Shen et al., 2004). Additionally, the fossiliferous horizon is located toward the base of the formation, and recently evidences of a hiatus with the overlying Early Cretaceous Rivera Member were discovered (Soto, 2016). Thus, we regard a Late Jurassic age more likely than a Late Jurassic-Early Cretaceous age. The specimen from Tacuarembó is also the oldest ctenochasmatid pterosaur in South America. Indeed, as already mentioned the other South American members of this family come from Early Cretaceous deposits from Argentina and Chile (Bonaparte, 1970; Chiappe et al., 2000; Martill et al., 2006) (Fig. 7). The Uruguayan occurrence shows that already in the Late Jurassic ctenochasmatids had reached South America, due to their capacity of displacement through flight. Jurassic pterosaurs from South America (and Gondwana) are scarcely represented (Fig. 7A). The Middle Jurassic Cañadón Asfalto Formation yielded Allkaruen koi Codorniú et al., 2016, the sister taxon to Monofenestrata, whereas the Late Jurassic Vaca Muerta Formation yielded the pterodactyloids Herbstosaurus pigmaeus Casamiquela, 1975 and Wenupteryx uzi Codorniú and Gasparini, 2013. Hence, the Uruguayan occurrence is a valuable addition to the Jurassic record of South American pterosaurs.

Acknowledgements The data and images of the scans were acquired in the Laboratório Multiusuário de Processamento de Imagens de Microtomografia Computadorizada de Alta Resolução do Museu de Zoologia da Universidade de São Paulo. We thank Hussam Zaher and Alberto Carvalho for allowing and training to the use of such equipment. Sebastián Tambusso provided a great help with graphic softwares. Andrea Corona, Aldo Manzuetti, Andrés Batista, Sofía Alonso, Natalia Correa, Camila Fogliani, and Florencia Pereyra collaborated in the field work. Paul Pursglove and Emma Bernard provided useful advice on pterosaur teeth. A preliminar CT scan of the specimen FC-DPV 2869 was carried out at the Unidad de Radiología - Hospital de Clínicas (Universidad de la República) through the assistance of Víctor Ezquerra. Detailed comments by two reviewers significantly improved an original draft of this manuscript. This work was partially supported by project FCE2014_104620/ANII/Uruguay.

5.2. Paleoecological implications Ctenochasmatid pterosaurs, with their comb-like dentition formed by numerous needle-like teeth, are regarded as filter feeders (Wellnhofer, 1991; Unwin, 2006) or show also other strategies as the transition from insectivorous/piscivorous to filter-feeding (Witton, 2013; Zhou et al., 2017). Particularly, Gnathosaurus long jaws and curved teeth formed a filter basket for small aquatic organisms (Wellnhofer, 1991). Wading habits were suggested for members of this pterosaur family (Witton, 2013), and probable food sources for them, 304

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Fig. 7. Paleogeographic maps depicting distribution of ctenochasmatid specimens. A, Late Jurassic (150 Ma). B, Early Cretaceous (120 Ma). 1. Gnathosaurinae gen. et sp. indet., Tacuarembó Formation, Late Jurassic-?earliest Cretaceous of Tacuarembó (Uruguay). 2. Kepodactylus insperatus, Morrison Formation, Late Jurassic of Colorado (USA). 3. Gnathosaurus macrurus and Plataleorhynchus streptophorodon, Tithonian-Berriasian of Purbeck Limestone, Dover (England). 4. Gnathosaurus subulatus, Ctenochasma elegans and Aurorazhdarcho micronyx, Solnhofen Limestone, Tithonian of Bavaria, and C. roemeri, "Purbeck", Berriasian of Saxony (Germany). 5. Ctenochasma taqueti, Calcaires tâchetés, Tithonian of Haute-Marne (France). 6. Huanhepterus quinyangensis, Huachihuanhe Formation, Late Jurassic of Gansu (China). 7. Liaodactylus primus, Tiaojishan Formation, Oxfordian of Liaoning (China). 8. ?Gnathosaurinae gen. et sp. indet., Early Cretaceous of Atacama (Chile). 9. Pterodaustro guinazui, Lagarcito Formation, Albian of San Luis (Argentina). 10. Beipiaopterus chenianus, Cathayopterus grabaui, Elanodactylus prolatus, Eosipterus yangi, Feilongus youngi, Gegepterus changi, Moganopterus zhuiana and Pterofiltrus qiui, Yixian Formation, Aptian of Liaoning, and Gladocephaloideus jingangshanensis and Forfexopterus jeholensis, Jiufotang Formation, Early Cretaceous of Liaoning (China). Maps reproduced with permision of Deep Time Maps. Stratigraphic and locality data taken from several sources (e.g. Dong, 1982; Howse and Millner, 1995; Martill et al., 2006; Wang and Zhou, 2006; Wang et al., 2007; Jiang and Wang, 2011; Andres et al., 2014; Jiang et al., 2016; Zhou et al., 2017).

Appendix A. Supplementary data

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