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

Using modern taxa to understand biomechanical variables: Interpreting function from fossil footprints


1Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 2Human Origins Program, National Museum of Natural History, Smithsonian Institution, 3Hominid Paleobiology Doctoral Program, The George Washington University, 4Department of Biology, James Madison University

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The uniqueness of extinct species presents a profound obstacle to reconstructing function from fossilized remains. While researchers often study functional morphology in modern species to make inferences about function in extinct species, inherent assumptions must be made when attempting to use modern taxa as models for extinct ones. We argue that the most productive approach involves understanding the variables in biomechanical systems such that those variables can be investigated in extinct taxa, even when they have unique morphologies. Here, we provide an example of this approach with our efforts to interpret foot function and anatomy from footprints made by extinct hominins 1.52 million years ago at FwJj14E near Ileret, Kenya.

To better understand how gait and foot shape and function influence footprint formation, we conducted experiments with thirty-eight habitually unshod and minimally-shod Daasanach adults who walked and ran across a pressure pad and made footprints in rehydrated fossil footprint sediment excavated from an Ileret footprint layer. At walking speeds, the depths within footprints show a significant relationship (p<0.0001) with peak pressure across most anatomical locations. Interestingly, fossil footprint shapes (relative depths) differed significantly from those of the experimental footprints, despite the comparable sizes and speeds of the prints made by the Daasanach subjects walking on the same sediment. Instead of using modern human samples as "models" from which to infer function, we suggest that unique gait and/or foot anatomy can be interpreted via an understanding of the relationships among the variables, such as pedal pressures, gait parameters, and footprint structure.

This study was funded by the National Science Foundation grants BCS-0924476 and DGE-0801634, Cotlow Award, GW Gamow Fellowship, and the GW University Facilitating Fund.

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