The Role of Mechanical Function in the Evolution of Skeletal Morphology

Abstract

The role of mechanical function in the evolution of morphology is important to our understanding of the dynamics of morphological macroevolution. Our understanding of the fossil record and therefore Earth’s natural history is largely based on morphological evidence. Many epistemological arguments have been discussed regarding what should be assumed about morphological adaptation to function, ranging from an assumption that all structures are optimised, to an assumption that no structure is. In this thesis, I develop upon previous methodologies such as theoretical morphology, Pareto optimality and biomechanics, to test whether morphological structures are optimised or not, and to measure the relative strength of functional bias on form. I apply this to a wide range of 2D vertebrate jaw morphologies throughout their fossil record, and find that many of these jaws are optimised within the trade-off for rotational efficiency and stress dissipation in response to biting. Furthermore, I find a negative correlation between optimality and complexity in the theoretical morphospace of mammal jaws, which provides a mechanism through which natural selection can actively reduce complexity over time. Finally, I develop
more models for the theoretical morphology of 3D biological ‘tubes’, such as the shaft of the humerus in birds. These algorithms are intended to be broadly applicable to a wide range of biological structures. The morphology of the limb shaft is constrained in aquatic and aerial birds compared to terrestrial and insessorial birds. I conclude in this thesis that theoretical morphology is an extremely powerful tool in modern evolutionary biology, and more work is needed to develop new morphological models and apply their concepts to a
wide range of biological structures. The role of mechanical function in skeletal morphology is testable in certain structures like the jaw, and with more development, we can ask similar questions of many biological forms.

Date of Award	3 Oct 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Emily J Rayfield (Supervisor) & Philip C J Donoghue (Supervisor)