Craniofacial gracilisation within Homo sapiens and its relationship to masticatory loading

Crabtree, Kira L.

Abstract

It is frequently proposed that differences in craniofacial form are selectively and plastically driven by dietary differences, with species that consume mechanically challenging items having adaptations that increase bite force and optimise gape capacities, while also reducing strains experienced under masticatory loading. Paleoanthropologists commonly describe the crania of ancestral Homo species (such as Homo ergaster) as more robust that the crania of modern Homo sapiens. Interestingly, one area of increased robusticity in H. ergaster is the zygoma region, a key structure of the masticatory apparatus. Whether this zygoma region morphology is more optimal for consuming a mechanically challenging diet (relative to the morphology of H. sapiens) has yet to be investigated, nor have the global impacts of having a more robust zygoma region on craniofacial strains.
This thesis uses finite elements analysis to investigate the impact of simulating different masticatory loads, and changes in zygoma region morphology on craniofacial strains in a H. sapiens cranium. This involved constructing a H. sapiens cranial finite element model and subsequently using virtual anatomy techniques to create a hypothetical model containing H. ergaster-like zygoma regions. By comparing craniofacial strains, the efficiency of the jaw-elevator muscles, and bite force predictions in both models, the functional significance of the H. ergaster-like zygoma region is explored.
It is demonstrated that the zygoma region morphology of H. ergaster may be an adaptation to increase bite force and to reduce strains locally during bites at large gapes, however its importance in lowering strains during all masticatory loading scenarios remains questionable. It is therefore concluded that the gracile zygoma region of H. sapiens may be less of direct product of a release on selective pressures maintaining traits that reduce craniofacial strains, but consequential to less frequently performing bites at large gapes and reduced selective pressures on having large jaw-elevator musculature.

Citation

Crabtree, K. L. Craniofacial gracilisation within Homo sapiens and its relationship to masticatory loading. (Thesis). Hull York Medical School. https://hull-repository.worktribe.com/output/4790670

• Thesis Type: Thesis
• Deposit Date: Aug 22, 2024
• Publicly Available Date: Aug 22, 2024
• Keywords: Medicine
• Public URL: https://hull-repository.worktribe.com/output/4790670
• Additional Information: Hull York Medical School; University of Hull and University of York
• Award Date: Sep 1, 2023