This thesis investigates the determinants, mechanical implications, and evolutionary significance of mandibular mass distribution in ungulate-grade mammals. The mass properties of the mandible (i.e., mass, centre of mass, and rotational inertia) govern the energetic efficiency of mastication and the mechanical stresses acting on the masticatory system. Despite their importance, these properties remain poorly quantified in comparative studies. Here, new computed tomography (CT) based and surface model-based methods are developed and validated to estimate mandibular mass distribution with high precision and reproducibility. Validation against an established analogue method demonstrates close agreement, confirming that CT-derived estimates are accurate and data derived from either method are statistically interchangeable.
Using these techniques, interspecific and ontogenetic datasets of ungulate-grade mammals (Orders Artiodactyla, Perissodactyla, Proboscidea) were analysed to evaluate scaling relationships between anatomical and mechanical metrics (i.e., mandible length, mass, centre of mass, rotational inertia, masseter insertion area, mechanical advantage of the adductor musculature). Results show that rotational inertia scales with positive allometry relative to mandible length, indicating that larger taxa possess disproportionately higher resistance to angular acceleration. Adjustments for habitual head posture reveal that an anteriorly downward mandible orientation reduces effective rotational inertia and the mechanical cost of chewing, an effect which is most pronounced in grazing and large-bodied species. Additional analyses show that the masseter insertion area and mechanical advantage scale isometrically, maintaining functional efficiency across size ranges. Comparative results from extinct and extant taxa demonstrate continuity in these biomechanical patterns through the Cenozoic, linking morphological diversity to ecological adaptations in feeding behaviour and energetics.
Collectively, the findings establish a robust methodological and theoretical framework for integrating mandibular mass distribution into functional and evolutionary analyses of mammalian masticatory mechanics. The study highlights the interplay between biomechanics, ecology, and evolution in shaping the morphology, function, and performance of the mammalian mandible.
