title: The Evolution of Body Shape and Locomotion in Archosauria
Creators: name: Macaulay, SA
Publisher: name: University of Liverpool Repository
Year: 2019

description: Locomotion is essential to the survival of all organisms. Extant animals display a broad range of adaptations to a wide range of locomotor behaviours. Locomotion can be observed directly in living animals, but this is not the case for fossil taxa which are known from only skeletal material. An indirect route is therefore required to access this information on locomotor capabilities. Centre of mass is a key biomechanical parameter which effectively summarises body shape. Body shape influences, and is influenced by, the locomotor capabilities of an organism. Due to these close links, centre of mass has considerable potential value as an indirect route to information on locomotion in extinct species. One group of particular interest is Archosauria, which contains a host of unusual animals such as Diplodocus, Pterodactylus and Tyrannosaurus. However, there are several obstacles which currently prevent centre of mass being used to its full potential in investigations of fossil taxa. Firstly, existing methods for estimating centre of mass position in fossils are limited either by substantial subjectivity, or by a lack of data on extant archosaurs. Additionally, the interpretation of any resulting predictions of centre of mass is hindered by a poor understanding of the links between centre of mass and specific locomotor behaviours, especially in volant organisms. It is therefore recognised that in order for the field to progress, more data are required on extant archosaurs. This thesis seeks to address this issue by collecting a series of novel datasets on living archosaurs which are used as the foundation for improved predictions and interpretations of centre of mass data in extinct archosaurs. Three commonly used methods for centre of mass estimation in physical specimens were assessed in order to determine their absolute accuracies. The scales and digital methods were found to have high levels of accuracy and repeatability. Due to method specific limitations when applied to biological specimens, I concluded that the digital method is the preferred solution for this thesis. One benefit of digital modelling is the ease of alteration; small details can be added to models, but this is a time consuming process. This thesis examined the impact of different levels of model detail on whole body centre of mass. For example, air cavities (included as standard in current models), were found to exert less influence on centre of mass than a feathered integument (which has never before been quantified), calling standard modelling practices into question. Using digital models of 27 bird species, links were explored between centre of mass position and locomotor type. Species using volant behaviours were found to have more ventral centres of mass than their terrestrial counterparts; though this difference was not significant after accounting for phylogeny. This would provide greater manoeuvrability in flight. Finally, a new method for centre of mass estimation in fossils was developed and applied to fossil taxa. Compared to previous work, this method produced different centres of mass, with greater error margins. This is despite the fact that this new method benefits from greater objectivity and a quantitative grounding based on data from extant archosaurs. This suggests that previous studies have underestimated the biological variation present and their results should therefore be interpreted with caution. This thesis provides the foundation for further work to continue to build towards better methods for centre of mass estimation in extinct taxa, and more confident biological interpretations of the resulting predictions.