The evolution of ceratopsians

Abstract

The Ceralopsia is a group of herbivorous, beaked dinosaurs from the Late Cretaceous. In my PhD thesis, I carried out research on the evolution of ceratopsians through bone histology and numerical analysis. Based on numerous specimens of Psittacosaurus iujialunensis in different ontogenetic stages. a bone histological study of ontogenetic growth in Psittacosaurus lujiatunensis shows some differences from Psittacosaurus mongoliensis. Bone thin sections from individuals of particular ontogenetic ages revealed some novel aspects of dinosaur behaviour, such as posture shift and juvenile-only clusters. Numerical analyses on phylogeny, diversity and disparity show the macroevolutionary patterns of ceralopsians. "The mechanism of postural shift in Psittacosaurus is revealed by histological study, and the transition from quadrupedality to bipedality appears to have occurred at about age 2. Juvenile-only clusters in Psittacosaurus, ranging from five to 34 individuals, and with evidence for a variety of ages in at least one specimen (IVPP V14341) suggests some unique juvenile-only behaviour. Tbe series of thin sections from P. lujiatunensis indicated five types of bone tissue and four histological ontogenetic stages, i.e., batchling, juvenile, sub-adult, and adult. None of the specimens was fully-grown. P. mongoliensis and P. lujiatunensis are similar in external morphology, but their growth patterns in terms of bone histology show several differences. According to the cladistic analysis, which combines basal and derived ceratopsians for the first time, Chaoyangsaurus youngi is the most basal ceratopsian, and Yinlong downsi is the most basal neoceratopsian, instead of Chaoyangsaurus youngi. The diversity research supports the idea that the major large-bodied herbivorous ceratopsians endured about 5 Ma of decline in taxonomic diversity before their extinction. In the disparity research, basal neoceratopsians occupied the largest rnorphospace compared to later groups, suggesting considerable anatomical specialization through the Late Cretaceous.

Date of Award	2013
Original language	English
Supervisor	Michael J Benton (Supervisor)