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


Shape exploration of the third metacarpal capitate facet: implications for early hominin morphology

THOMAS R. REIN and KATERINA HARVATI.

Paleoanthropology Section, Department of Early Prehistory and Quaternary Ecology, Senckenberg Center for Human Evolution and Paleoecology, Eberhard Karls Universität Tübingen

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The manus is useful in inferring the manipulative and locomotor capabilities of early hominins since the hand grasps objects and directly interacts with the substrate during non-bipedal locomotion. Based on observed differences in third metacarpal (Mc3) base morphology, it has been hypothesized that great apes are adapted for stabilization during locomotion, whereas humans are adapted for manipulative behaviors. Researchers have also noted shape differences in the proximal end of the Mc3 between modern humans and Australopithecus afarensis. One difference is the shape of the capitate facet, which narrows palmarly in A. afarensis relative to modern humans and great apes. The purpose of this research is to explore this difference in a wider comparative context to enhance our understanding of this distinct morphology in Australopithecus afarensis.

We collected three-dimensional landmark coordinates on the Mc3 capitate facet in 12 extant species using a Microscribe digitizer. We collected comparable data on Proconsul heseloni and Australopithecus afarensis. We explored shape variation using principal components analysis and examined covariation between shape and locomotion using partial least-squares. Australopithecus afarensis facet shape was similar to that of cercopithecoids and platyrrhines. We also found that distantly related brachiators, Hylobates and Ateles, had similar facet shapes that were distinct from other anthropoids. Based on this research, we have uncovered a functional signal in this morphology related to brachiation. We also found that, while Australopithecus afarensis facet shape is unique within the hominoid clade, it is similar to a range of extant anthropoids.

This study was funded by the German Academic Exchange Service (DAAD), grant number A0981106, National Science Foundation, grant number BCS-0849204, the L.S.B. Leakey Foundation, the Wenner-Gren Foundation, and the Margaret and Herman Sokol Postdoctoral Fellowship, New York University.

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