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ANATOMY AND SYSTEMATICS OF COELUROSAURIAN THEROPODS FROM THE LATE JURASSIC OF XINJIANG, CHINA, WITH COMMENTS ON FORELIMB EVOLUTION IN THEROPODA Open Access

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Coelurosauria is a group of theropod dinosaurs that includes birds and their close relatives. Ghost lineages indicate coelurosaurian diversification by the Middle Jurassic (Bathonian). Unfortunately, this time period has a poor coelurosaurian fossil record and the anatomy and systematics of stratigraphically early and phylogenetically basal coelurosaurs remain poorly understood. Recent excavations of the Late Jurassic (Oxfordian/Callovian) Shishugou Formation in Xinjiang, northwestern China recovered four new coelurosaurian theropod taxa, providing a rare window into early coelurosaurian morphology. In this dissertation, I describe two new species of Shishugou coelurosaur, and document the anatomy of the basal tyrannosauroid Guanlong wucaii and the basal alvarezsauroid Haplocheirus sollers. I present new information on the anatomy of Nqwebasaurus thwazi, a basal coelurosaur from the Early Cretaceous of South Africa. I incorporate the information from this anatomical research into a large, broadly-sampled phylogenetic data matrix of the Theropoda, and use it to test the phylogenetic relationships of the Shishugou coelurosaurs and the monophyly of Coelurosauria. The results of my analysis support the monophyly of Coelurosauria, the tyrannosauroid affinities of Guanlong, and the alvarezsauroid affinities of Haplocheirus. I recover the two other Shishugou taxa as basal members of Coelurosauria and Nqwebasaurus as the basalmost member of Ornithomimosauria. I investigate the phylogenetic history of forelimb length in theropods by calculating ratios of forelimb length relative to femoral length (a proxy for body size), and reconstructing the ancestral states for these ratios on my phylogeny. This investigation shows that the forelimb was independently reduced a minimum of four times in theropod evolution, that the common ancestor of Oviraptorosauria and Paraves had a relatively long forelimb, and that the common coelurosaurian ancestor had about the same relative forelimb length as the common theropod ancestor. In theropods with relatively short forelimbs, the humerus contributes proportionately more to forelimb length than it does in theropods with relatively long forelimbs. My results support coelurosaurian diversification by the early Late Jurassic, extend the fossil record of alvarezsauroids by 63 million years, establish the presence of ornithomimosaurs in Gondwana, and indicate that a relatively long forelimb did not characterize the most basal coelurosaurs.

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