Browsing by Author "Ji, Shu'an."
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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 Juvenile birds from the early Cretaceous of China : implications for enantiornithine ontogeny ; American Museum novitates, no. 3594(New York, NY : American Museum of Natural History, 2007) Chiappe, Luis M.; Ji, Shu'an.; Ji, Qiang.Mesozoic remains of embryonic and early juvenile birds are rare. To date, a handful of in ovo embryos and early juveniles of enantiornithines from the early Cretaceous of China and Spain and the late Cretaceous of Mongolia and Argentina have comprised the entire published record of perinatal ontogenetic stages of Mesozoic birds. We report on the skeletal morphology of three nearly complete early juvenile avians from the renowned early Cretaceous Yixian Formation of Liaoning Province in northeastern China. Evidence of the immaturity of these specimens is expressed in the intense grooving and pitting of the periosteal surfaces, the disproportionately small size of the sterna, and the relative size of the skull and orbits. Size notwithstanding, anatomical differences between these three specimens are minimal, leaving no basis for discriminating them into separate taxa. Numerous osteological synapomorphies indicate that they are euenantiornithine birds, the most diverse clade of Enantiornithes, but their identification as members of a particular euenantiornithine taxon remains unclear. Their early ontogenetic stage, however, provides important information about the postnatal development of this specious clade of Cretaceous birds. The presence of pennaceous wing feathers suggests that fledging occurred very early in ontogeny, thus supporting a precocial or highly precocial strategy for enantiornithine hatchlings. The morphology of these new early-stage juveniles is also significant in that they allow a better understanding of the homologies of several avian compound bones because the components of these skeletal compounds are preserved prior to their coossification. The general morphology of the wrist and ankle of these juveniles highlights once again the striking similarity between nonavian theropods and early birds.Item Ordosemys (Testudines, Cryptodira) from the Yixian Formation of Liaoning Province, northeastern China : new specimens and systematic revision. American Museum novitates ; no. 3438(New York, NY : American Museum of Natural History, 2004) Tong, Haiyan.; Ji, Shu'an.; Ji, Qiang.; Zhongguo di zhi bo wu guan.The Yixian Formation, in Liaoning Province, northeastern China, has yielded abundant turtle remains which were described previously as Manchurochelys liaoxiensis. Study of a new collection in the Geological Museum of China and reexamination of previously studied IVPP collection allow us to assign this turtle to Ordosemys. Additional primitive features observed in Ordosemys liaoxiensis confirm its basal position among Centrocryptodira.