The braincase of ceratopsian dinosaurs

Abstract

Ceratopsia is a diverse and geologically widespread suborder of ornithischian dinosaurs. A dearth of braincase data has plagued ceratopsian studies for over a century and the number of phylogenetic braincase studies has remained stagnant and dubious. Ceratopsian braincase descriptions often are incorporated into broader descriptive papers and, when they are the focus of the study, they often lack easily digestible figures. The individual elements that form the ceratopsian endocranial cavity wall, or ‘braincase’, and their interrelationships have rarely been studied within a 3D environment. Using 3D reconstruction, morphological descriptions and statistical analyses, the structure of the ceratopsian braincase and morphology of the semicircular canal pathway is visualised through ontogeny and from several taxa across the clade.
Braincase characters are included in most phylogenetic studies of Ceratopsia, but their utility and the effect they have on tree topology have gone unstudied. In this thesis, the utility of braincase characters within ceratopsian phylogenetic studies is investigated via a selection of statistical congruence tests.
Results demonstrate that braincase elements undergo morphological changes through growth, with the majority of the changes occurring towards the rear of the braincase to support the enlarged crania of adult ceratopsians. The semicircular canal morphology further supports the evidence that Psittacosaurus underwent a postural shift through growth. A dramatic difference in basisphenoid orientation and paroccipital process morphology is documented between the braincases of ceratopsians at the base of the clade, Yinlong and Psittacosaurus, and a derived member of the Ceratopsidae, Medusaceratops. Finally, when analysed separately, the braincase characters are revealed to poorly reflect the topology of the ceratopsian phylogenetic tree, suggesting their utility in ceratopsian phylogenetics in their current state is minimal.

Date of Award	2 Dec 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Michael J Benton (Supervisor), Qi Zhao (Supervisor), Michael J Ryan (Supervisor) & Jakob Vinther (Supervisor)