The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Cortical structure of hallucal metatarsals and inferring foot loading in early Homo


1Evolutionary Studies Institute, University of the Witwatersrand, 2School of Geosciences, University of the Witwatersrand, 3Department of Anthropology, Indiana University, 4Department of Geology and Palaeontology, Georgian National Museum, 5School of Statistics and Actuarial Science, University of the Witwatersrand

March 27, 2015 1:45, Grand Ballroom E/F/G Add to calendar

Loading experienced by modern human feet differs substantially from that of other apes, likely reflecting different foot configurations (e.g., adducted versus abducted hallux) and weight transfer mechanisms. Internal structure of hallucal metatarsal diaphyses presumably reflects these differences in loading history. By applying a recently demonstrated morphological approach for visualizing and quantifying continuous cortical bone properties of diaphyses, we compare internal structure of hallucal metatarsals from apes and two Dmanisi individuals. Specifically, we test whether Dmanisi first metatarsals exhibit modern human patterns of cortical bone distribution, or whether these human patterns emerged more recently. For each hallucal metatarsal, 17 cross sections were extracted at regularly-spaced intervals between 25% and 65% mechanical length. Cortical thicknesses in cross sections were measured in one degree radially-arranged increments, while second moments of area (SMAs) and section moduli (SMs) were measured about neutral axes in one degree radially-arranged increments. Standardized thicknesses, SMAs, and SMs were visualized using false color maps, while penalized discriminant analyses were used to evaluate group differences. Overall, Dmanisi hallucal metatarsals exhibit ape-like levels of thickness. Although Dmanisi specimens themselves differ in thickness distributions, visualized patterns in thicknesses are neither human-like nor ape-like. Comparisons of continuous SMAs and SMs indicate that Dmanisi hallucal metatarsals are uniquely reinforced compared to apes, but are most like humans and australopiths (e.g., StW562 and SKX5017). Modern human loading patterns experienced by hallucal metatarsals appear to have not yet fully emerged in Dmanisi hominins, possibly also implying the existence of a difference in toe off.

ESI and CoE in Palaeosciences (Wits), Department of Science and Technology (SA), and National Research Foundation (SA) provided funding. Claude Leon Foundation and SPARC (Wits) funded a post-doctoral fellowship (TJ).