The First Discovery of Pterosaurs from the Upper Cretaceous of Mongolia

The first discovery of pterosaurs from the Upper Cretaceous of Mongolia MAHITO WATABE, TAKANOBU TSUIHIJI, SHIGERU SUZUKI, and KHISHIGJAV TSOGTBAATAR Watabe, M., Tsuihiji, T., Suzuki, S., and Tsogtbaatar, K. 2009. The first discovery of pterosaurs from the Upper Creta− ceous of Mongolia. Acta Palaeontologica Polonica 54 (2): 231–242. DOI: 10.4202/app.2006.0068 Cervical vertebrae of azhdarchid pterosaurs were discovered in two Upper Cretaceous (Baynshire Suite) dinosaur locali− ties, Bayshin Tsav and Burkhant, in the Gobi Desert. These are the first discoveries of pterosaur remains in the Upper Cre− taceous of Mongolia. The Burkhant specimen includes a nearly complete atlas−axis complex, which has rarely been de− scribed in this clade of pterosaurs. Although all elements comprising this complex are fused together, a wing−like atlas neural arch is still discernable. The postzygapophyseal facet of the axis is long anteroposteriorly and convex dorsally, and would likely have allowed a fairly large range of dorsoventral flexion at the axis−third cervical joint unlike in other well−known ornithocheiroids such as Pteranodon and Anhanguera. Both Mongolian localities represent inland, terres− trial environments, which were apparently not typical habitats of pterosaurs, thus adding further evidence for the ubiquity of Azhdarchidae during the Late Cretaceous. Key words: Pterosauria, Azhdarchidae, Late Cretaceous, Gobi Desert, Mongolia. Mahito Watabe [[email protected]−net.ne.jp] and Shigeru Suzuki [[email protected]], Center for Paleobiological Research, Hayashibara Biochemical Laboratories, Inc., 1−2−3 Shimoishii, Okayama 700−0907, Japan; Takanobu Tsuihiji [[email protected]], JSPS Research Fellow, Department of Geology, National Museum of Nature and Science, 3−23−1 Hyakunin−cho, Shinjuku−ku, Tokyo 169−0073, Japan; Khishigjav Tsogtbaatar [[email protected]], Mongolian Paleontological Center, Mongolian Academy of Sci− ences, Enkh Taivan Street−63, Ulaanbaatar 210351, Mongolia. Introduction sell 1991; Hicks et al. 1999). These remains were found during field seasons from 1993 to 2004 of the Hayashibara Museum Pterosaur remains in Mongolia are very scarce. In the 1970’s of Natural Sciences−Mongolian Paleontological Center Joint and 1980’s, remains of many individuals of the dsungaripterid Paleontological Expedition, and mark the first discoveries of “Phobetor” parvus (generic name preoccupied) including a pterosaurs from the Upper Cretaceous in Mongolia. These re− complete skull were found from the Lower Cretaceous in mains can be assigned to Azhdarchidae Nessov, 1984, and provide new data on stratigraphic and geographic distribution Tatal of the Sangiin Dala Nuur depression (Khovd Aimag) by of pterosaurs in the Late Cretaceous. the Joint Soviet−Mongolian Paleontological Expedition (Bak− Measurement method on these cervical vertebrae is shown hurina and Unwin 1995; also see Unwin and Bakhurina 2000 in Fig. 2, with measurements reported in Table 1. for further discussion of the taxonomic status of this ptero− saur). Later, pterodactyloid remains were discovered by the Institutional abbreviations.—FMNH, Field Museum of Natu− same Joint Expedition in Khuren Dukh in Central Gobi Aimag ral History, Chicago, Illinois, USA; MPC, Mongolian Paleon− (upper Lower Cretaceous), and were referred to Ornitho− tological Center, Mongolian Academy of Sciences, Ulaan− cheiridae (Bakhurina and Unwin 1995). In addition, a frag− baatar, Mongolia; NSM−PV, Division of Vertebrate Paleon− mentary, small−sized anurognathid pterosaur was found from tology, National Museum of Nature and Science (formerly the middle Jurassic beds of Bakhar in Bayankhongol Aimag of National Science Museum), Tokyo, Japan; TMM, Texas Me− central Mongolia (Bakhurina and Unwin 1995). Most re− morial Museum, University of Texas at Austin, Austin, Texas, cently, a cervical vertebra of a tapejaroid (sensu Kellner 2003) USA; YPM, Peabody Museum of Natural History, Yale Uni− pterosaur was discovered at the Lower Cretaceous Öösh local− versity, New Haven, Connecticut, USA. ity by the Joint Mongolian−American Expedition (Andres and Norell 2005). To date, however, no pterosaur remains have been discovered in the Upper Cretaceous in the Mongolian Geological setting territory (Fig. 1). We here describe pterosaur remains from the Baynshire Bayshin Tsav.—This locality is situated 95 km southeast of Suite (early Late Cretaceous) in Burkhant and Bayshin Tsav in Manlai Somon and 64 km northeast of Khan Bogd Somon in the eastern region of the Gobi Desert (Jerzykiewicz and Rus− the eastern part of Southern Gobi Aimag (Fig. 1). This locality Acta Palaeontol. Pol. 54 (2): 231–242, 2009 DOI: 10.4202/app.2006.0068 232 ACTA PALAEONTOLOGICA POLONICA 54 (2), 2009 92 100 108 116 reddish brown mudstone. In hard sandstone layers, there are 50 RUSSIA many trough cross−stratifications showing direction of an an− cient stream. The paleocurrent indicated by these cross−strat− ifications is roughly parallel to the strike of gently tilted beds 4 Ulaanbatar of sandstone and mudstone. The beds containing vertebrate 46 fossils are interpreted as point bar deposits of a meandering MONGOLIA river. Other vertebrate remains found from the same locality 5 6 3 Saynshand include associated skeletal elements of a sauropod (Watabe 1 et al. 2000), dromaeosaurid Achillobator giganticus (Perle et 42 Dalanzadgad 2 al. 1999), and several turtle taxa. The age of the fossiliferous beds is not yet clearly determined. Based on the similar li− CHINA thology and geographic proximity, however, these beds have 300 km been correlated with the Upper Cretaceous Baynshire Suite in Khongil Tsav, 11 km north of the locality, and Bayn Shire, Fig. 1. Geographic distribution of pterosaur localities in Mongolia. 1, Burk− hant (Upper Cretaceous, Eastern Gobi Aimag); 2, Bayshin Tsav (Upper 9 km southeast of the locality (Perle et al. 1999). Crertaceous, Southern Gobi Aimag); 3, Khuren Dukh (Lower Cretaceous, Central Gobi Aimag); 4, Tatal (Lower Cretaceous, Khovd Aimag); 5, Bakhar (Upper Jurassic–Lower Cretaceous, Bayankhongor Aimag); 6, Öösh (Lower Cretaceous, Övörkhangai Aimag). Systematic paleontology is best known for occurrences of three therizinosauroid thero− Pterosauria Kaup, 1834 pods: Enigmosaurus mongoliensis, Erlikosaurus andrewsi, Pterodactyloidea Plieninger, 1901 and Segnosaurus galbinensis (Perle 1979, 1981; Barsbold and Azhdarchidae Nessov, 1984 Perle 1983). In addition, several other dinosaur taxa have been found from this locality, including the ornithomimid Garudi− Bayshin Tsav azhdarchid mimus brevipes, indeterminate small (dromaeosaurid?) and Figs. 3, 4. large theropods, and an indeterminate primitive hadrosaur Material.—MPC−Nd 100/303, an isolated middle cervical (Barsbold 1981; Watabe et al. 2000). Remains of turtles are vertebra with the posterior end missing from Bayshin Tsav, also abundant. east of Southern Gobi Aimag, Mongolia, Bayn Shire Suite, A pterosaur cervical vertebra was found in a bone bed in early Late Cretaceous (Cenomanian–Santonian). the northwestern part of this locality. The outcrops in this area consist of alternating thin layers of fining−upward units (from Description coarse sands to mud) intercalated by many layers of yellowish The specimen is fairly well−preserved although the posterior brown to reddish brown, coarse−grained sandstone and fine− end of the element including the postzygapophyses and pos− grained conglomerate, probably representing point bar depos− terior articular surface of the centrum is missing. The verte− its. The bone bed is one of the bluish white, fine− to coarse− bra is greatly elongated anteroposteriorly. The preserved grained sandstone layers that alternate with gray mudstone portion of the centrum is about 5.6 times as long as the mini− layers, containing isolated bones and teeth of hadrosaurs and mum width of the vertebra at its mid−length, and the total small theropods that were transported and accumulated by an length of the preserved portion of the vertebra including ancient stream. prezygapophyses is about 3.1 times as long as the maximum The sediments of this locality have been assigned to the width across the prezygapophyses. There is no recognizable lower Upper Cretaceous Baynshire Suite by Shuvalov and suture line between the neural arch and centrum, which to− Chikhikvadze (1975) and Ivakhnenko and Kurzanov (1988). gether form a tube−like main body of the vertebra. No pneu− Paleomagnetic analyses by Hicks et al. (1999) gave the matic foramen is present on its lateral aspect. On the anterior Baynshire Suite the chronological range of the Cenomanian aspect of the neural arch, however, there is a pneumatic fora− to Santonian, providing an age constraint for the pterosaur men lying lateral to the neural canal on each side. The neural specimens from Bayshin Tsav and Burkhant (see below) de− spine is ridge−like and very low along most part of the neural scribed here. arch. However, the height of the neural spine, as well as the Burkhant.—Horizontal, fossiliferous beds form small out− width of its base, increases at the posterior end. Only the base crops in this locality, which is located in Eastern Gobi Aimag, of the neural spine is preserved on the anterior end of the neu− 69 km and 22 km southwest of the towns of Saynshand and ral arch, but it is wider than that in the middle to posterior Dzunbayan, respectively (Fig. 1). The new pterosaur speci− parts, suggesting that the neural spine would also have in− men consisting of four associated cervicals was found in

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