Browsing by Author "Gao, Keqin, 1955-"
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Item Braincase and phylogenetic relationships of Estesia mongoliensis from the late Cretaceous of the Gobi Desert and the recognition of a new clade of lizards. American Museum novitates ; no.3211(New York, N.Y. : American Museum of Natural History, 1997) Norell, Mark.; Gao, Keqin, 1955-; Mongolyn Shinzhlėkh Ukhaany Akademi.Item An early ostrich dinosaur and implications for ornithomimosaur phylogeny. American Museum novitates ; no. 3420(New York, NY : American Museum of Natural History, 2003) Ji, Qiang.; Norell, Mark.; Makovicky, Peter J.; Gao, Keqin, 1955-; Ji, Shu'an.; Yuan, Chongxi.A new ornithomimosaur from the Yixian Formation of Liaoning Province Peoples Republic of China is described. These beds are near the Jurassic-Cretaceous boundary. This specimen is interesting because it has several primitive characters for ornithomimosaurs such as teeth and a short first metacarpal. This taxon is placed in a phylogenetic analysis of Coelurosauria and shown to be near the base of the ornithomimosaur clade. Using this phylogeny we comment on the biogeographic history of this group.Item A new choristodere from the Cretaceous of Mongolia. American Museum novitates ; no. 3468(New York, NY : American Museum of Natural History, 2005) Ksepka, Daniel T.; Gao, Keqin, 1955-; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The remains of a choristodere recently discovered at Two Volcanoes, a new locality in the Gobi Desert of Mongolia, are described in this paper. Consisting of a fairly complete skull and partial postcranial skeleton, this specimen represents a new species of the genus Tchoiria. The new species differs from Tchoiria namsarai in having a much smaller number of teeth. Several elements preserved in this specimen are unknown in T. namsarai and thus provide new information about the genus. Phylogenetic analysis with the addition of data from the new specimen confirms the basal position of Tchoiria in Simoedosauridae.Item A new crown-group frog (Amphibia, Anura) from the early Cretaceous of northeastern Inner Mongolia, China. (American Museum novitates, no. 3876)(American Museum of Natural History., 2017-03-14) Gao, Keqin, 1955-; Chen, Jianye.Based on 12 well-preserved skeletons of postmetamorphic individuals, a new crown-group frog taxon is named and described from the Lower Cretaceous Guanghua (upper part of Longjiang) Formation (stratigraphic equivalent of the world-famed Yixian Formation) exposed in Dayangshu Basin, Hulunbuir, in the far northeast of Inner Mongolia, China. The new taxon, Genibatrachus baoshanensis, documents another early Cretaceous anuran having reduction of the presacral vertebrae to eight in number, similar to several frog taxa of roughly the same age from Spain and Brazil. The new frog also displays several features that are ontogenetically and phylogenetically informative, including ontogenetic fusion of the palatine to the sphenethmoid, and ontogenetic fusion of ribs to the diapophyses of the posterior trunk vertebrae. In addition, the new discovery extends the geographic range of early Cretaceous frogs of the Jehol Biota northward to near the 50th parallel north in East Asia.Item A new nonmammalian eucynodont (Synapsida, Therapsida) from the Triassic of northern Gansu Province, China, and its biostratigraphic and biogeographic implications. (American Museum novitates, no. 3685)(American Museum of Natural History., 2010) Gao, Keqin, 1955-; Fox, Richard C.; Zhou, Chang-Fu.; Li, Da-Qing.A new trirachodontid eucynodont, Beishanodon youngi, is named and described based on a well-preserved skull from Triassic lacustrine deposits exposed in the Beishan Hills, northern Gansu Province, China. The new discovery documents the second record of trirachodontid eucynodonts known from China, along with Sinognathus gracilis from the Middle Triassic Ermaying Formation exposed in Shanxi Province. Cladistic analysis supports the placement of the new taxon as the sister group of Sinognathus, and the two together can be classified in Sinognathinae, a new subfamily differentiated from other trirachodontids by possession of several derived character states, including extremely short snout and strongly expanded temporal region. In addition, the stratigraphic and biogeographic significance of the new discovery are discussed. Because trirachodontids have a restricted stratigraphic range in the Triassic, as best documented by the Cynognathus Assemblage Zone of South Africa, discovery of the new fossil of this group from northern Gansu Province in China provides definitive evidence for a Triassic age of the fossil-bearing beds exposed in the Beishan Hills; moreover, the fossil beds are assessed as early Triassic in age based on the evidence from the entire vertebrate fauna.Item A new platynotan lizard (Diapsida, Squamata) from the late Cretaceous Gobi Desert (Ömnogöv), Mongolia ; American Museum novitates, no. 3605(New York, NY : American Museum of Natural History, 2008) Norell, Mark.; Gao, Keqin, 1955-; Conrad, Jack L.Item A new specimen of Microraptor (Theropoda, Dromaeosauridae) from the Lower Cretaceous of western Liaoning, China. (American Museum novitates, no. 3821)(American Museum of Natural History., 2014-12-22) Pei, Rui.; Li, Quanguo.; Meng, Qingjin, 1962-; Gao, Keqin, 1955-; Norell, Mark.Microraptor zhaoianus is known from several specimens collected in western Liaoning Province, China. However, several aspects of the morphology of Microraptor remain unknown or ambiguous due to poor preservation of the described specimens. A well-preserved new specimen of Microraptor zhaoianus is described in this study. This specimen preserves significant morphological details that are not present or are poorly preserved in the other Microraptor specimens including aspects of the skull, the rib cage, and the humerus. These new characters corroborate Microraptor as a member of the Dromaeosauridae as previously suggested and support the close relationship of troodontids and dromaeosaurids (Deinonychosauria). The morphology of the rib cage also suggests Microraptor and the early volant avialans very likely may have shared a similar mechanism to assist respiration.Item New specimens of Anchiornis huxleyi (Theropoda, Paraves) from the late Jurassic of northeastern China. (Bulletin of the American Museum of Natural History, no. 411)(American Museum of Natural History., 2017-04-13) Pei, Rui.; Li, Quanguo.; Meng, Qingjin, 1962-; Norell, Mark.; Gao, Keqin, 1955-Four new specimens of Anchiornis huxleyi (PKUP V1068, BMNHC PH804, BMNHC PH822, and BMNHC PH823) were recently recovered from the late Jurassic fossil beds of the Tiaojishan Formation in northeastern China. These new specimens are almost completely preserved with cranial and postcranial skeletons. Morphological features of Anchiornis huxleyi have implications for paravian character evolution and provide insights into the relationships of major paravian lineages. Anchiornis huxleyi shares derived features with avialans, such as a straight nasal process of the premaxilla and the absence of an external mandibular fenestra in lateral view. However, Anchiornis huxleyi lacks several derived deinonychosaurian features, including a laterally exposed splenial and a specialized raptorial pedal digit II. Morphological comparisons strongly suggest Anchiornis is more closely related to avialans than to deinonychosaurians or troodontids. Anchiornis huxleyi exhibits many conservative paravian features, and closely resembles Archaeopteryx and other Jurassic paravians from Jianchang County, such as Xiaotingia and Eosinopteryx. The other Jianchang paravian, Aurornis xui, is likely a junior synonym of Anchiornis huxleyi.Item New specimens of Microraptor zhaoianus (Theropoda, Dromaeosauridae) from northeastern China. American Museum novitates ; no. 3381(New York, NY : American Museum of Natural History, 2002) Hwang, Sunny H.; Norell, Mark.; Ji, Qiang.; Gao, Keqin, 1955-New specimens of the diminutive theropod dinosaur Microraptor zhaoianus are described. These specimens preserve significant morphological details that are not present or are poorly preserved in the holotype specimen, including aspects of the manus, pectoral girdle, dorsal vertebrae, ilium, and sacrum. These specimens were coded into a current matrix of theropod morphological characters. Microraptor is found to be the sister taxon to other dromaeosaurs. Dromaeosaurids are monophyletic and together with a monophyletic troodontid group form a monophyletic Deinonychosauria, which is the sister taxon to Avialae. Apparently small size is primitive for Deinonychosauria, which has implications for bird origins.Item Taxonomic composition and systematics of late Cretaceous lizard assemblages from Ukhaa Tolgod and adjacent localities, Mongolian Gobi Desert. Bulletin of the AMNH ; no. 249([New York] : American Museum of Natural History, 2000) Gao, Keqin, 1955-; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Upper Cretaceous deposits at Ukhaa Tolgod and adjacent localities in the Mongolian Gobi Desert have yielded a large number of superbly preserved lizard specimens, including representatives of several new taxa (described in this paper) and important supplementary material of several previously poorly known taxa. Study of these specimens gives important insight into the taxonomic diversity and systematics of the Late Cretaceous lizard fauna of the Gobi Desert. A preliminary survey indicates that the lizard assemblage from Ukhaa Tolgod and adjacent localities consists of some 30 species in four higher groups (Iguania, Gekkota, Scincomorpha, and Anguimorpha). The iguanians are documented by eight species, including three species newly recognized in this paper. The Scincomorpha are the most diverse group, represented by as many as 14 species including three new and 11 previously known species. The Anguimorpha are nearly as diverse as the Iguania, while the Gekkota is the least diverse group with a single species documented in the assemblage. The scincomorphs include forms that are highly specialized for burrowing life-styles, interpreted from their cranial morphology as possibly analogous to extant species. The anguimorphs include phylogenetically important basal members of several major anguimorph clades. The paleoecological significance of these lizards cannot be overlooked. According to tooth morphology, most lizards are predatory in terms of habit, while true herbivorous species are rare. Most specimens are preserved as skulls articulated with mandibles, but virtually complete skeletons in situ are quite common. Delicate parts of the skull, such as the braincase and ear ossicles, are undistorted and the surfaces of the bones show no sign of sand abrasion. These observations indicate not only relatively quick burial but also burial under relatively mesic climatic conditions with low-energy water involved during the taphonomic process.Item Taxonomic revision of Carusia (Reptilia, Squamata) from the late Cretaceous of the Gobi Desert and phylogenetic relationships of anguimorphan lizards. American Museum novitates ; no. 3230(New York, NY : American Museum of Natural History, 1998) Gao, Keqin, 1955-; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi."New specimens of lizards collected by the Mongolian Academy of Sciences-American Museum of Natural History Expeditions from the Gobi Desert include a large sample of superbly preserved cranial material of Carusia intermedia. Study of these specimens resolves problematic aspects of the cranial morphology and phylogenetic relationships of this poorly known lizard taxon. Analyses of 105 morphological characters across 30 selected ingroup and three outgroup taxa yield a phylogeny. This result refutes a previously suggested ?Scincomorphan relationship of Carusia, instead supporting placement of this taxon in the Anguimorpha. A new lizard clade including the basal Carusia and the crown group Xenosauridae is recognized. This clade occupies the basalmost position within the Anguimorpha. Recognition of this taxon as a basal anguimorphan resolves the Xenosauridae/Anguidae/Varanoidea polytomy. Relationships of platynotan taxa known from the Gobi Desert are also discussed and problems with these taxa are addressed"--P. [1].