Macroevolutionary and Ontogenetic Trends in the Anatomy and Morphology of the Non-Avian Dinosaur Endocranium

Abstract

The subfield of dinosaur palaeoneurology describes and compares the function and form of neuroanatomy in non-avian dinosaur taxa. Currently, palaeoneurologists have collected nearly 100 partial and complete reconstructed endocasts – the internal soft tissue space of the braincase (Chapter 1). From these endocrania, palaeontologists have been able to explore the relationship between the brain, behaviour, palaeoecology, and trophic ecology of adult non-avian dinosaurs (Chapter 2). However, immature specimens from an ontogenetic series are rarely published upon due to their rarity in the fossil record. Similarly, our understanding of postnatal ontogenetic development in extant taxa is frequently referred to in the literature, but very few studies describe or compare full ontogenetic series of modern archosaur endocrania. By understanding how the morphology and relative sizes of endocrania change with developmental age in modern taxa, palaeoneurologists can apply the same methods to interpret extinct taxa (Chapter 3). Surprisingly, when a complete ontogenetic series of a nonavian dinosaur (Psittacosaurus lujiatunensis) endocrania is compared to patterns in modern archosaurs, the endocasts diverge from established avian or crocodilian developmental patterns (Chapter 4). This indicates limitations in our understanding of how the brains or endocasts change shape, flexure, and anatomical size with age in extinct taxa. This shows the importance of determining the age of endocranial specimens – and especially if the endocast is being used in macroevolutionary studies. To emphasize this point, the juvenile endocast of P. lujiatunensis is convergent in form with bird endocasts (Chapter 5). This underlines how little is known about the relationship between the non-avian endocranium, paedomorphosis, and heterochrony when comparing adult bird endocasts to non-avian dinosaurs.

Date of Award	24 Jun 2021
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Michael J Benton (Supervisor) & Emily J Rayfield (Supervisor)