A Re-Examination of Psittacosaurus Lujiatunensis Using Modern Techniques

Psittacosaurus is one of the most specimen-rich dinosaurs known, and the large number of specimens provides a unique opportunity to better understand dinosaurs at the specific level through quantitative statistical analyses as well as qualitative primary description. Intraspecific diversity in dinosaurs is little known as the majority of dinosaurs are based on single, often incomplete specimens. In this dissertation Psittacosaurus is examined using geometric morphometrics, qualitative osteological description, traditional morphometrics, and bone histology. Geometric morphometric analyses demonstrate that taphonomic postmortem distortion drives the location in morphospace of each specimen and obscures true biologic shape, making assessments of intraspecific and ontogenetic variability in P. lujiatunensis difficult. Comparisons with a modern, undeformed dataset show that taphonomic deformation can account for up to 30% of observed shape variation in P. lujiatunensis. These studies demonstrate that taphonomy is a critical factor to consider in geometric morphometric-based studies of shape changes in fossil organisms. I also examine a small monospecific deposit that includes a large Psittacosaurus specimen and twenty-four juveniles, and describe it using osteological, histologic, and taphonomic methods to elucidate morphological and microstructural changes that occur during Psittacosaurus ontogeny as well as determine the burial history of the deposit. Finally, though this particular bonebed assemblage has been interpreted as a possible nesting structure, I provide taphonomic evidence, including petrographic thin sections and x-ray diffraction of the surrounding rock, that suggests that the animals were more likely entombed by a fluvial or lahar flow.