Khishigjav Tsogtbaatar

A new enantiornithine bird from the Late Cretaceous of the Gobi Desert

Synopsis We report on a new species of enantiornithine bird from the Late Cretaceous of the Mongolian Gobi Desert, which adds to the meager record of birds from the latest part of the Mesozoic in this region. The exceptional, three‐dimensional bones of the new fossil increase the known anatomical diversity of enantiornithine birds, providing information about previously unreported morphologies such as a pneumatised furcula. Several synapomorphies nest the new bird within an enantiornithine clade of proficient fliers, but the anatomy and proportions of its flight apparatus imply significant aerodynamic restrictions. The combination of phylogeny and our functional interpretation suggests that this new fossil bird is a representative of a flightless lineage. This discovery thus provides the first evidence of a trend towards more limited flying capabilities among Enantiornithes, a group of Cretaceous birds otherwise believed to be represented by competent fliers.

Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia

ABSTRACT A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugjn Tsav locality in the Mongolian Gobi Desert is described. With a total length of 290 mm, the present specimen represents one of the smallest skulls known for this species. Not surprisingly, it shows various characteristics common to juvenile tyrannosaurids, such as the rostral margin of the maxillary fenestra not reaching that of the external antorbital fenestra and the postorbital lacking the cornual process. The nasal bears a small lacrimal process, which disappears in adults. Lacking some of the morphological characteristics that are adapted for bearing great feeding forces in adult individuals, this juvenile specimen suggests that T. bataar would have changed its dietary niches during ontogeny. The numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same as those in adults, suggesting that they do not change onto genetically in T. bataar and thus are not consistent with the hypothesis that the numbers of alveoli decreases ontogenetically in tyrannosaurids.

An exquisitely preserved troodontid theropod with new information on the palatal structure from the Upper Cretaceous of Mongolia

Troodontidae is a clade of small-bodied theropod dinosaurs. A new troodontid, Gobivenator mongoliensis gen. et sp. nov., is described based on the most complete skeleton of a Late Cretaceous member of this clade presently known, from the Campanian Djadokhta Formation in the central Gobi Desert. G. mongoliensis is different from other troodontids in possessing a pointed anterior end of the fused parietal and a fossa on the surangular in front of the posterior surangular foramen. The skull was superbly preserved in the specimen and provides detailed information of the entire configuration of the palate in Troodontidae. Overall morphology of the palate in Gobivenator resembles those of dromaeosaurids and Archaeopteryx, showing an apparent trend of elongation of the pterygoid process of the palatine and reduction of the pterygopalatine suture toward the basal Avialae. The palatal configuration suggests that the skull of Gobivenator would have been akinetic but had already acquired prerequisites for later evolution of cranial kinesis in birds, such as the loss of the epipterygoid and reduction in contact areas among bones.

Hyaenodon chunkhtensis and the hyaenodontid fauna from the upper Eocene Ergilin Dzo Formation of Mongolia

Hyaenodon Laizer and Parieu, 1838 is one of the most speciose genera of the Hyaenodontidae (Mammalia; Creodonta) and is widely distributed in the late middle Eocene to Oligocene of North America (Mellett, 1977; Gunnell, 1998), in the late Eocene to Oligocene of Europe (Lange-Badré, 1979; Schmidt-Kittler, 1987), and in the late middle Eocene to early Miocene of Asia (Russell and Zhai, 1987; Lange-Badré and Dashzeveg, 1989; Huang et al., 2001; Wang et al., 2005). Hyaenodon chunkhtensis Dashzeveg, 1985 is one of the six smallest species of Hyaenodon and is the smallest among the Asian species of Hyaenodon (Lavrov and Emry, 1998). So far, H. chunkhtensis had been reported only from the lower Oligocene Hsanda Gol ‘svita’ at the Shunkht locality of southern Mongolia (Dashzeveg, 1985). The upper Eocene Ergilin Dzo Formation of southeastern Mongolia has been famous for yielding many vertebrate fossils including several species of Hyaenodon (Matthew and Granger, 1923; Belyayeva et al., 1974; Dashzeveg, 1974, 1993; Yanovskaya et al., 1977). The mammals of this formation are the type fauna of the Ergilian (late Eocene) Asian Land Mammal Age (Russell and Zhai, 1987; McKenna and Bell, 1997; Meng and McKenna, 1998). Although in this formation several species of hyaenodontid creodonts have been reported (Matthew and Granger, 1925; Gromova, 1952; Dashzeveg, 1964, 1985; Lange-Badré and Dashzeveg, 1989; Lavrov, 1999), the number of taxa and generic and species names of the hyaenodontids from the formation are confused (Russell and Zhai, 1987; Polly, 1993; Wang et al., 2005; Morlo and Nagel, 2006; Egi et al., 2007). In this short article, we report H. chunkhtensis from the Ergilin Dzo Formation at the Khoer Dzan locality and briefly review the hyaenodontid fauna of the formation to clarify its current status. The specimen described here is a left mandible with p4–m3 discovered by the Hayashibara Museum of Natural Sciences and Mongolian Paleontological Center Joint Paleontological Expedition in 2004 (Tsubamoto, Watabe et al., 2006). The specimen was found by surface prospecting at a lower part of a slope of the locality, so that the precise stratigraphic horizon of the specimen within the formation cannot be determined. This discovery adds one more species to the hyaenodontid fauna of the formation. Institutional Abbreviations—AMNH, American Museum of Natural History, New York, USA; BDMAS, Biological Department of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia; HMNS, Hayashibara Museum of Natural Sciences, Okayama, Japan; MPC, Mongolian Paleontological Center, Ulaanbaatar, Mongolia; MPC-M, mammalian fossil collections stored in MPC; PIN, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia; PSS and PST, Paleontology and Stratigraphy Section, Geological Institute, Ulaanbaatar, Mongolia; SHG, specimens from the Shand Gol locality of central Mongolia stored in Vienna Museum, Vienna ( Wien), Austria. Anatomical Abbreviations—c, lower canine; M/m, upper/ lower molar; P/p, upper/lower premolar.

Cranial Ornamentation and Ontogenetic Status of Homalocephale calathocercos (Ornithischia: Pachycephalosauria) from the Nemegt Formation, Mongolia

ABSTRACT The cranial roof ornamentation and the degree of neurocentral closure in the holotype of the pachy cephalosaurian dinosaur Homalocephale calathocercos is described in detail for the first time in order to assess its ontogenetic status and taxonomic validity. The parietosquamosal ornamentation consists of five primary nodes along the posterior margin of the skull roof on each side of the midline. The medial-most node is prominently enlarged relative to the others in the series and is bisected by the parietal-squamosal suture. Beneath the primary node row, a second enlarged node occurs immediately medial to lateroventral corner node on each side of the parietosquamosal bar. The degree of suture closure in the vertebral column suggests that the holotype specimen of H. calathocercos is immature, rather than adult. The presence of cranial doming at maturity is therefore unknown in H. calathocercos, and hypotheses that it represents a primitive flat-headed stage in pachycephalosaur evolution or is pedomorphic in the development of its skull roof cannot be supported or refuted at this time. Despite the probable immaturity of the holotype, H. calathocercos has a unique pattern of parietosquamosal ornamentation that is distinct from all other pachycephalosaurs, including Prenocephale prenes from the same host formation. Morphological differences in the cranial ornamentation, jaws, and dentition between the similarly sized holotype skulls of H. calathocercos and P. prenes provide weak support for recent suggestions that H. calathocercos is conspecific with the latter taxon. This study tentatively reaffirms the presence of two pachycephalosaur species in the Nemegt Formation

The First Discovery of Pterosaurs from the Upper Cretaceous of Mongolia

Cervical vertebrae of azhdarchid pterosaurs were discovered in two Upper Cretaceous (Baynshire Suite) dinosaur localities, Bayshin Tsav and Burkhant, in the Gobi Desert. These are the first discoveries of pterosaur remains in the Upper Cretaceous of Mongolia. The Burkhant specimen includes a nearly complete atlas-axis complex, which has rarely been described 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, terrestrial environments, which were apparently not typical habitats of pterosaurs, thus adding further evidence for the ubiquity of Azhdarchidae during the Late Cretaceous.

New specimens of Protoceratops (Dinosauria : Neoceratopsia) from the Upper Cretaceous in Udyn Sayr, southern Gobi area, Mongolia

Abstract. Four skull specimens (MPC-D 100/537,100/538,100/539 and100/540) of Protoceratopsidae from the Upper Cretaceous in Udyn Sayr, Mongolia are described, and their ontogenetic stage and expression of sexual dimorphism are estimated. These specimens are identified as Protoceratops andrewsi (MPC-D 100/537, 100/539), P. cf. andrewsi (MPC-D 100/538), and Protoceratops sp. (MPC-D 100/540), respectively. MPC-D 100/537 and 100/539 are attributed to subadult “female” and MPC-D 100/538 to subadult “male”. MPC-D 100/540 is adult with unknown sex. Based on the frill morphologies, the Udyn Sayr specimens are classified into three types: type 1 (MPC-D 100/539), well developed ridge on the lateral surface of the squamosal; posteriorly projected posterior margin of the squamosal; type 2 (MPC-D 100/537), posteriorly rounded posterior margin of the squamosal; developed ridge on the posterior margin of the parietal; and type 3 (MPC-D 100/540), large size; posteriorly curved posterior margin of the squamosal; the rugose surface texture on the dorsal side of parietal. MPC-D 100/538 could not be categorized because the specimens frill is not preserved. These frill morphologies differ from those of Protoceratops from the Djadokhta Formation in the adjacent dinosaur locality Tugrikin Shire. The morphological differences among the Udyn Sayr specimens may indicate intraspecific variation of Protoceratops.

New specimens of anthracotheriid artiodactyls from the upper Eocene Ergilin Dzo Formation of Mongolia

Abstract We describe fossil specimens of two taxa of anthracotheriid artiodactyls (Mammalia) discovered in the upper Eocene Ergilin Dzo Formation of southeastern Mongolia and briefly review the late Eocene anthracotheriids of northern East Asia. The specimens described here are: (1) an upper molar, an astragalus, and a calcaneum of a small bunodont anthracotheriid; and (2) upper and lower postcanine dentitions, an astragalus, and a distal tibia of a Bothriodon/Aepinacodon-like selenodont anthracotheriid. This paper provides the first description and figures of the Anthracotheriidae from the formation, which were hitherto poorly understood. The anthracotheriid fauna of the formation currently consists of two species, an indeterminate bunodont anthracotheriid and cf. Bothriodon sp. This is the first discovery of a bunodont anthracotheriid in the late Eocene of the northern part of East Asia. The anthracotheriids are mainly represented by selenodont and bunoselenodont species and are rare faunal elements in the late Eocene of northern East Asia; in contrast, they are mainly represented by bunodont and bunoselenodont species and are predominant faunal elements in the late Eocene of southern East Asia. This implies a paleobiogeographical separation between the northern and the southern parts of East Asia during the late Eocene.

Perinatal Specimens of Saurolophus angustirostris (Dinosauria: Hadrosauridae), from the Upper Cretaceous of Mongolia

Background The Late Cretaceous Nemegt Formation, Gobi Desert, Mongolia has already yielded abundant and complete skeletons of the hadrosaur Saurolophus angustirostris, from half-grown to adult individuals. Methodology/Principal Findings Herein we describe perinatal specimens of Saurolophus angustirostris, associated with fragmentary eggshell fragments. The skull length of these babies is around 5% that of the largest known S. angustirostris specimens, so these specimens document the earliest development stages of this giant hadrosaur and bridge a large hiatus in our knowledge of the ontogeny of S. angustirostris. Conclusions/Significance The studied specimens are likely part of a nest originally located on a riverbank point bar. The perinatal specimens were buried by sediment carried by the river current presumably during the wet summer season. Perinatal bones already displayed diagnostic characters for Saurolophus angustirostris, including premaxillae with a strongly reflected oral margin and upturned premaxillary body in lateral aspect. The absence of a supracranial crest and unfused halves of the cervical neural arches characterize the earliest stages in the ontogeny of S. angustirostris. The eggshell fragments associated with the perinatal individuals can be referred to the Spheroolithus oogenus and closely resemble those found in older formations (e.g. Barun Goyot Fm in Mongolia) or associated with more basal hadrosauroids (Bactrosaurus-Gilmoreosaurus in the Iren Dabasu Fm, Inner Mongolia, China). This observation suggests that the egg microstructure was similar in basal hadrosauroids and more advanced saurolophines. Competing Interests One of the authors (FE) is employed by the commercial organization Eldonia. Eldonia provided support in the form of a salary for FE, but did not have any additional role or influence in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and it does not alter the authors’ adherence to all the PLoS ONE policies on sharing data and materials.

The Entelodontid Artiodactyl Fauna from the Eocene Ergilin Dzo Formation of Mongolia with Comments on Brachyhyops and the Khoer Dzan Locality

Abstract. We review the entelodontid artiodactyl fauna of the upper Eocene Ergilin Dzo Formation in southeastern Mongolia. Also, we describe new specimens of Brachyhyops trofimovi from the Khoer Dzan locality and review the characteristics and Asian distribution of Brachyhyops. The revised entelodontid fauna of the formation consists of three species: Entelodon gobiensis (from the Khoer Dzan and Ergilin Dzo localities), Brachyhyops trofimovi (from the Khoer Dzan locality), and Brachyhyops? sp. (from the Ergilin Dzo locality). The discovery of p4 and M2 of B. trofimovi demonstrates the definitive diagnostic characteristics of this species within the genus: p4 is buccolingually wide and is triangular in occlusal view; it has a well developed and high cusp (= hypoconid?), which is fused to the posterior part of the protoconid; and M2 has a better-developed pericone. In Asia, Brachyhyops is recorded only in the southern part during the middle Eocene and only in the northern part during the late Eocene, implying that the genus originated in the southern part of Asia and subsequently migrated northward, giving rise to northern Asian and North American Brachyhyops.