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

An experimentally-based interpretation of 1.5 million-year-old fossil hominin footprints: Implications for the evolution of human foot function


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

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Fossil hominin footprints preserve valuable information that can directly inform hypotheses regarding the evolution of human foot anatomy and gait. However, their interpretation requires an understanding of the complex interaction between foot anatomy, foot function, and soft sediment mechanics. We used an experimental approach to test the hypothesis that evidence of human foot function, specifically the distribution of plantar pressure, can be inferred from footprints. Then, we applied our experimental results to develop a comparative interpretation of c.1.5 million-year-old fossil hominin footprints at Ileret, Kenya.

Thirty-eight habitually unshod and minimally shod Daasanach individuals first walked across a pressure pad, then produced footprints in sediment directly excavated from the geological layer that preserves the fossil footprints at Ileret. Water was added to this sediment such that subjects consistently produced footprints of similar overall depth to the fossil prints, thereby best approximating conditions in which the fossil prints were formed. We found significant correlations (Spearman’s rank, p < 0.0001) between measurements of plantar pressure and relative footprint depths at ten anatomical regions across the foot. We took similar depth measurements from the Ileret fossil prints and compared them to the experimental sample. Significant differences were found between the experimental and fossil samples at multiple anatomical regions of the footprints (Mann-Whitney U, p < 0.05). Because sediment type and presumably sediment mechanics were constant, these differences may imply functional and/or anatomical differences between modern human feet and those of the hominins (likely Homo erectus or Paranthropus boisei) that produced the Ileret fossil footprints.

This study was funded by the National Science Foundation, grants BCS-0924476 and DGE-0801634. This research was approved by The George Washington University Institutional Review Board, #031030.

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