Diet and Mandibular Morphology in African Apes |
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Authors: | Andrea B Taylor |
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Institution: | (1) Department of Community and Family Medicine, Duke University School of Medicine; Department of Biological Anthropology, Duke University, Durham, North Carolina 27710, USA |
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Abstract: | Investigations seeking to understand the relationship between mandibular form, function, and dietary behavior have focused
on the mandibular corpus and symphysis. African apes vary along a gradient of folivory/frugivory, yet few studies have evaluated
the morphology of the mandibular corpus and symphysis in these taxa, and the investigations have yielded mixed results. Specifically,
studies using external metrics have identified differences in mandibular proportions that analysis of cortical bone distribution
has not substantiated. I contribute to the ongoing debate on the relationship between jaw form and dietary behavior by comparing
mandibular corporal and symphyseal shapes in African apes. Importantly, and in contrast to previous studies of African ape
internal geometry, I include the Virunga mountain gorillas (Gorilla beringei beringei), the ape most specialized toward a folivorous diet. I test the hypotheses that 1) Gorilla beringei beringei always has significantly more robust mandibular corpora and symphyses, relative to mandibular length, than all other African
apes and 2) all gorillas have significantly more robust mandibular corpora and symphyses, relative to mandibular length, than
Pan. Results demonstrate that the folivorous mountain gorillas consistently exhibit a relatively wider mandibular symphysis and
corpus than all other African apes. Furthermore, all gorillas consistently exhibit relatively more robust mandibular corporal
and symphyseal dimensions than Pan. The results indicate that among African apes, mountain gorillas are better able to counter lateral transverse bending (wishboning)
loads at the symphysis and torsional loads at the corpus. All gorillas are likewise better able to resist wishboning and vertical
bending at the symphysis, and sagittal bending and torsion at the corpus, than Pan, findings that are consistent with masticating relatively tougher foods, repetitive loading of the jaws, or both. I offer
possible explanations for the lack of concordance in results between studies that have analyzed the biomechanical properties
of African ape mandibles and others that have relied on external metrics. More comprehensive study of the internal geometry
of the mandible is needed to resolve whether African apes differ morphologically in ways predicted by dietary variation.
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Keywords: | diet African apes chimpanzees gorillas mandible symphysis corpus |
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