Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, Baltimore
Saturday All day, Plaza Level
There has been considerable debate regarding the extent to which early hominins exhibited a walking pattern similar to that of modern humans. A previous study incorporating hip and femoral dimensions of A.L. 288-1 into a biomechanical model of modern human gait predicted increased joint reaction forces and greatly increased gluteal abductor forces and M-L bending of the femoral shaft; however, this is not supported by the overall morphology of A.L. 288-1. One explanation for these findings is that early hominins exhibited increased pelvic tilt (up on the non-support side) during walking, which would have decreased abductor and joint reaction forces and reoriented the center of mass closer to the femoral head. This would also create a more vertical hip joint reaction force, increasing bending and decreasing compressive loading of the femoral neck and thereby leading to a less asymmetric (more ape-like) distribution of cortical bone in the neck. To test this hypothesis, we measured superior and inferior cortical thickness of femoral neck bases and mid-regions of eight early South African hominins from CT scans and compared the results with reported values for modern humans and non-human primates. Superior to inferior cortex ratios for the early hominins were found to be intermediate between modern humans and non-human apes at the base and more similar to non-human apes in the mid-neck. This result is consistent with a more vertical joint reaction force acting on the femoral head and an altered gait pattern among at least some early hominins.