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Title: Cranial morphology and masticatory biomechanics in the Canidae
Author: Penrose, Fay
ISNI:       0000 0004 7964 1926
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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Cranial form is closely allied to diet and feeding behaviour in the Canidae, with the force and velocity of jaw closing depending on both the bony morphology of the skull and mandible, and the mass and architecture of the jaw adductor muscles. Previously, little has been reported on the details of the form and function of the jaw adductor muscles, with earlier studies basing functional biomechanical hypotheses on data derived from dry skull specimens. For this study, empirically derived muscle data was recorded from 12 species of wild canid to examine how the jaw adductor muscles are scaled across the range of body sizes, phylogenies and trophic groups. I also considered how the muscles are accommodated on the skull, and how this is influenced by differences of endocranial size. Findings reveal that all jaw adductor muscles scale isometrically against body mass, regardless of phylogeny or trophic group, but that endocranial volume scales with negative allometry against body mass. Gross dissection techniques were used to explore the architecture of the muscles, and findings were used to inform the building of finite element models that predict bite force and strain energy density values. The inclusion of muscle architectural detail is shown to influence masticatory muscle force production capability calculations, indicating that muscles with longer fascicles were disadvantaged compared to muscles with shorter fascicles. Dietary groups were differentiated by temporalis fascicle angles, which, when allied with the differentiation of rostral length, may further contribute to specialisations of fast jaw closing or forceful jaw closing species. The most biomechanically demanding masticatory function is canine biting, and the highest strain energy values were reported in these loading conditions, particularly in the zygomatic arches and caudal rostrum. Specific head shapes may be constrained by size, with scaled strain energy density models predicting that some bony morphologies may only be viable in species with small body masses. Lastly, ex vivo laboratory experiments and in silico models were used to explore the role of a previously underreported structure, the postorbital ligament, during biting. This study found that the postorbital ligament plays a minimal role in attenuating stress during mastication and that it need not be included in any future FEA bite force studies in canids. This work provides both original data and methodological recommendations for future projects. It is hoped that these findings can help to inform future studies on masticatory function in extant and extinct wild canid species and domesticated canid breeds.
Supervisor: Jeffery, Nathan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral