The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)


Evolutionary change in the hominin orbit: an analysis of orbital morphology in relation to neurocranial expansion and reduced facial prognathism since the middle Pliocene

MICHAEL P. MASTERS.

Anthropology / Liberal Studies, Montana Tech

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The principal aim of this study is to examine variation in orbital morphology in relation to long-term evolutionary trends of cranial expansion and reduced facial prognathism during hominin evolution. The orbit has not been investigated in the context of these morphological shifts, but is important to understand given its position amid these coalescing craniofacial features.

Samples used in this analysis include Pan troglodytes, Australopithecus africanus, Homo erectus, Archaic Homo sapiens, and anatomically modern Homo sapiens, each representing different grades of cranial expansion and facial prognathism. Orbital, neurocranial, and facial measures were taken from original specimens and casts at museums in South Africa, France, Monaco, and the United States, and were size-adjusted prior to analysis to account for body size differences among groups. Linear Regression and Principal components analysis were used to examine variation in orbital size/shape relative to cranial size and degree of facial prognathism.

All orbital traits were found to vary in association with change in these features, becoming vertically shorter, horizontally elongated, more frontated, and retracted relative to basion, with a greater degree of posterior reduction in the inferior orbital margins. These changes would be expected in association with the brain expanding and moving anteriorly out over the orbits, while the lower face retracts posteriorly toward them. Future research should employ high resolution imaging techniques to examine variation in size and shape of the internal aspects of the orbit, particularly given the degree to which the forebrain has grown out over this feature in recent human evolution.

This research was funded by a Grant In Aid of Research from The National Academy of Sciences, Administered by Sigma Xi; and from a Travel Grant administered by the Anthropology Department at The Ohio State University in Columbus, Ohio.

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