bulletin de l'institut royal des sciences naturelles de belgique sciences de la terre, 69-supp. b: 17-36, 1999 bulletin van het koninklijk belgisch instituut voor natuurwetenschappen aardwetenschappen, 69-supp. b: 17-36, 1999 A new species of the ankylosaurid dinosaur Pinacosaurus from the Late Cretaceous of Inner Mongolia (P.R. China) by Pascal GODEFROIT, Xabier PEREDA SUBERBIOLA, LI Hong & DONG Zhi-Ming Abstract A well-preserved articulated skeleton of an ankylosaurian dinosaur from the Late Cretaceous of Bayan Mandahu (Inner Mongolia) is described. The specimen consists of the skull, lower jaws and a great part of the postcranial skeleton, including the cervical armour and tail- Pinacosaurus mephi¬ club in place. This material is referred to the ankylosaurid genus Pinacosaurus Gilmore, 1933. A new species, P. mephistocephalus, stocephalus , ÎÔfîT Gilmorefél933^^I8iÉ#45l$ is erected on the basis of significant différences mainly in the nostril région relative to P. grangeri Gilmore, 1933. The new specimen, probably a subadult individual. provides further data about the com¬ position and arrangement of the dermal armour of Pinacosaurus. Moreover, the comparisons with both young and adult specimens of Pinacosaurus allow a better understanding of ontogenetic changes in mm- m., this dinosaur. Key-tvords: Ankylosauria, Pinacosaurus, Late Cretaceous, Inner Mongolia. mM m ±àm mu Résumé Le squelette articulé bien conservé d'un dinosaure ankylosaurien Introduction provenant du Crétacé supérieur de Bayan Mandahu (Mongolie in¬ térieure) est décrit. Le spécimen comporte le crâne, la mandibule et une grande partie du squelette post-crânien, y compris la cuirasse The ankylosaurid Pinacosaurus is a relatively common cervicale et la massue caudale en place. Ce matériel est rapporté à component of the Late Cretaceous dinosaur faunas of the Tankylosauridé Pinacosaurus Gilmore, 1933. Une nouvelle espèce, P. Gobi Basin mephistocephalus, est érigée sur la base de différences significatives, (Maryanska, 1977; Jerzykiewicz & Rus- notamment au niveau du museau, par rapport à P. grangeri Gilmore, sell, 1991). Gilmore (1933b) erected Pinacosaurus 1933. Le nouveau spécimen, en l'occurrence un individu subadulte, grangeri on the basis of an incomplete skull (AMNH fournit de nouvelles données quant à la composition et à l'arrangement 6523) from the Djadokhta Formation of de la cuirasse dermique de Pinacosaurus. De plus, une comparaison Bayn Dzak entre spécimens immatures et adultes de Pinacosaurus permet une (called Shabarakh Usu in American literature), in Outer meilleure compréhension des variations ontogénétiques chez ce dino¬ Mongolia. This specimen was discovered in 1923 by saure. the second Central Asiatic Expédition of the American Museum Mots-clés: Ankylosauria, Pinacosaurus, Crétacé supérieur, Mongolie (Andrews, 1932; Gilmore, 1933b). Other intérieure. specimens of this species, mainly the skull and asso- ciated postcranial skeleton of a juvénile individual (ZPAL MgD-II/1), were collected from the same locality and beds by the Polish-Mongolian Expédition in 1964 (Maryanska, 1971) and in other localities of the Mon- golian Gobi Basin by the Soviet-Mongolian Expéditions ("Syrmosaurus viminicaudus" Maleev, 1952; Tuma- nova, 1987). In Inner mm Mongolia (R.P. China), the Bayan Mandahu locality has yielded a herd of young Pinacosaurus during field activities undertaken by the Sino-Canadian Dino- 18 Pascal GODEFROIT et al. Fig. 1 — Generalized map of the central part of the Inner Mongolia Autonomous Région, showing the itinerary of the Sino-Belgian expéditions in 1995 and 1996. Inset map shows the Inner Mongolia Autonomous Région. saur Project in 1988 and 1990 (Dong et al., 1989; Currie, Geological setting 1991; Dong, 1992, 1993a). Currte (1991) also reported the discovery in 1990 of embryonic remains of Pinaco- The Bayan Mandahu badlands of Inner Mongolia lie on saurus in another site of Inner Mongolia. the northern flank of the Lang Shan (Wolf Mountains), A new Pinacosaurus specimen from the Bayan Man- near Urad Houqi, in the southern Gobi Basin (Figures 1 dahu site is described herein. The specimen, an articu- and 2). This site was discovered in 1978 by members of lated skeleton with a well-preserved skull, was discov- the Inner Mongolia Museum at Hohhot (Dong et al., ered during the second excavation campaign of the Sino- 1989). Since 1987 field work has been undertaken there Belgian Dinosaur Expédition in surnmer 1996 (Gode- by the Sino-Canadian Dinosaur Project (Dong, 1993a) roit et al., 1998). It represents a new species of Pinaco¬ and, more recently, by the Sino-Belgian Dinosaur Expé¬ saurus. dition (Godefroit et al, 1998). The lithofacies of the Bayan Mandahu Formation are Abbreviations: AMNH, American Museum of Natural mainly horizontally-bedded red sandstones. Several kinds History, New York; IMM Inner Mongolia Museum, of deposits, including eolian, interdune, lacustrine, pedo- Hohhot; IRSNB, Institut Royal des Sciences Naturelles genic and alluvial fans or braid plain, have been distin- de Belgique/ Koninklijk Belgisch Instituut voor Na¬ guished in the sections (Eberth, 1993). Articulated ske¬ tuurwetenschappen, Brussels; PIN, Palaeontological In- letons are common and occur associated within eolian stitute of the Russian Academy of Sciences, Moscow; deposits, whereas rare and fragmentary remains occur PIUU, Paleontologiska Institutionen, University of Up- within alluvial deposits (Jerzykiewicz et al., 1993). psala; ZPAL, Zaklad Paleobiologii, Polish Academy of The vertebrate assemblage of Bayan Mandahu includes Sciences, Warsaw. lizards, amphisbaenians, turtles, crocodilians, dinosaurs A new species of the ankylosaurid dinosaur Pinacosaunis 19 and mammals (Dong, 1992, 1993a; Jerzykiewicz et al., 1993). The dinosaurian fauna is dominated by protocer- atopsians, mainly Protoceratops. Pinacosaurus, the only known ankylosaurid of the Bayan Mandahu assemblage, is the second most common dinosaur. Theropods ( Velo- ciraptor, Oviraptor, Saurornithoides) are very rare. Pro¬ toceratops and Pinacosaurus include specimens that re- present all ontogenetic stages, including juvéniles and embryos (Currie, 1991; Dong, 1993a; Jerzykiewicz et al., 1993). They primarily occur as articulated and asso- ciated skeletons in structureless sandstones. The "stand¬ ing" position of the skeletons, including the Pinaco¬ saurus specimen described herein, suggests that the ani¬ mais died in situ and were probably buried alive during violent sandstorm events (Jerzykiewicz et al., 1993). An alternative hypothesis is a rapid déposition on dune-sand alluvial fans during rain storm episodes (see Loope et al., 1998). The occurrence of trace fossils such as borings in vertebrate skeletal remains, as these observed in the new Pinacosaurus specimen, is a common feature of eolian deposits at Bayan Mandahu (Jerzykiewicz et al., 1993). Articulated dinosaur skeletons from the Djadokhta For¬ mation of the Gobi Basin are often extensively bored. Even if the identity of the borers is unknown, it has been suggested that the borings were made by carrion insects (Kirkland et al., 1998). The lower diversity of the vertebrate assemblage and the overall small to moderate size of dinosaurs indicate a stressed palaeoenvironment. The sedimentological data suggest that the Bayan Mandahu redbeds were deposited in a semiarid climate in alluvial to eolian environments (Eberth, 1993). According to Jerzykiewicz et al. (1993), the fossil assemblages and lithofacies of the Bayan Man¬ dahu redbeds can be correlated with the type section of the Djadokhta Formation at Bayn Dzak (pre-Aldai Gobi, south-central Mongolia). Since the first description of the Djadokhta beds by Berkey & Morris (1927), the age of this formation has been abundantly discussed by numer- ous authors. An excellent summary of the conflicting hypotheses is given by Lillegraven & McKenna (1986), who suggest that the Djadokhta Formation could be synchronous of the lower part of the Judithian "North American Land Mammal Age"; according to Jerzykie¬ wicz & Russell (1991), this would indicate that the Djadokhta sédimentation began during the middle Cam- panian and took place during an interval centred on approximately 78 Ma ago. Nevertheless, it must be kept in mind that these conclusions, mainly based on compar- isons of vertebrate faunas, remain conjectural by lack of palynofloral, radioisotopic or palaeomagnetic data in the Gobi Basin. Fig. 2 — Simplified map of Bayan Mandahu area (modifïed after Eberth, 1993). Roman numbers indicate the fossil localities excavated during the Sino-Bel- gian expédition in 1996. The type locality of Pina¬ 2 km cosaurus mephistocephalus is indicated by an ar- row. 20 Pascal GODEFROIT et al. Systematic palaeontologv tive to the Djadokhta Formation, Campanian, Late Cre- taceous. Dinosauria Owen, 1842 Ornithischia Seeley, 1887 Derivatio nominis: Mephisto, abridged name for Me- Thyreophora Nopcsa, 1915 phistopheles, the name in Faust's legend of the devil Ankvlosauria Osborn, 1923 who made a pact with him; kephalê (Greek): head. The Family Ankylosauridae Brown, 1908 head of the holotype of Pinacosaurus mephistocephalus Genus Pinacosaurus Gilmore, 1933 reminds a devil's head. Type species: Pinacosaurus grangeri GiLMORE, 1933. Diagnosis: Two pairs of premaxillary foramina leading to premaxillary sinuses; "gland" opening facing ros- Emended generic diagnosis: Premaxilla excavated by a trally; both lower and upper premaxillary foramina much pair of large and rounded "gland openings"; low sub- smaller than