The feeding ecology of Mesozoic mammals

: A biomechanical approach

Abstract

Over 150 million years of mammalian evolution occurred in the Mesozoic. Mammalian diet knowledge helps us understand the ecological structure of terrestrial communities and prevailing environmental conditions. Jaws are commonly preserved in the fossil
record and inform on diet. In this thesis, I set out to investigate the relationship between jaw functional performance and diet in small mammals, using a combination of biomechanics, geometric morphometrics and phylogenetic comparative methods. Firstly, I used a combined approach of 2D form and function. I analysed the jaw shape of small extant mammals of known diets and the mechanical advantage of their adductor muscles. The combination of these data revealed differences in form and function between herbivores, carnivores, and insectivores. I found a very good correspondence between previously proposed diets of Mesozoic mammals and the results of this analysis. Secondly, I wanted to use a 3D approach to the study of jaw functional performance using Finite Element Analysis (FEA), commonly used in palaeontology to study feeding behaviour. FEA largely uses tomography-based models, which are expensive and time-consuming. Therefore, I decided to validate the use of simplified 3D models (called extruded models) built from photographs using two early mammal jaws as a case study. I found extruded models to be a viable alternative for large scale FEA studies. Thirdly, I used extruded FE models to study jaw functional performance in modern small mammals. I found differences in stress distribution between insectivores, hypercarnivores, mesocarnivores, and herbivores: most Mesozoic mammals resembled insectivores, and a few hypercarnivores. Put together, modern small mammals of different diets can be distinguished using jaw shape, mechanical advantage values, and stress distribution patterns. We can use this information to infer diet in Mesozoic mammals. Jaw functional performance corroborates the hypothesis that most Mesozoic mammals were insectivores, and a few taxa were carnivores.

Date of Award	23 Mar 2021
Original language	English
Awarding Institution	University of Bristol
Sponsors	CONACyT
Supervisor	Emily J Rayfield (Supervisor), Christine M Janis (Supervisor) & Pamela G Gill (Supervisor)