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

The effects of trunk morphology on bipedal locomotion in chimpanzees (Pan troglodytes)


1Department of Anatomical Sciences, Stony Brook University School of Medicine, 2Department of Basic Medical Sciences, University of Arizona College of Medicine, 3Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 4School of Health Technology and Management, Stony Brook University

March 27, 2015 11:30, Grand Ballroom A/B Add to calendar

Functional interpretations of the earliest known hominins have often drawn attention to differences in trunk morphology that characterize apes, humans and fossil hominins. Chimpanzees are seen as having rigid lumbar regions that are entrapped by projecting iliac blades. The aim of this study is to test the hypothesis that chimpanzees are characterized by truncal immobility by documenting three-dimensional motion of the thorax, lumbar region, and pelvis in humans and chimpanzees during bipedal locomotion at similar dimensionless speeds. Marker clusters on each segment were recorded using a four-camera motion capture system (Xcitex Inc., Boston, MA), and were used to calculate tilt, list, and rotation of each segment.

Initial results indicate that differences exist in the phasing and range of motion (ROM) of trunk segments between chimpanzees and humans. In the frontal plane, the entire chimpanzee trunk listed over the stance side limb, whereas humans exhibited minimal lumbar motion, a small thoracic list over the stance limb, and a drop of the pelvis to the unsupported side. In the transverse plane, and in contrast to humans, the chimpanzee thorax rotated in phase with the lumbar region and pelvis. However, rotation of the chimpanzee thorax was reduced ~40% relative to rotation of the pelvis, indicating a trunk that is not completely immobile. Differences in segmental ROM and phasing were less striking in the sagittal plane. These results highlight the effects of the derived human trunk, and will allow us to evaluate how pelvic and vertebral morphology may have affected motion in fossil hominins.

Supported by NSF BCS-0935321 and The Leakey Foundation