Center for Functional Anatomy and Evolution, Johns Hopkins Univ. School of Medicine
March 26, 2015 , Gateway Ballroom 2
Structural analyses of the femoral neck and diaphysis suggest that hip joint reaction force was reduced relative to body mass in australopiths compared to modern humans and early Homo. If true, this implies that body mass estimates derived from femoral head size in modern human reference samples may be too large in australopiths. Consistent with this hypothesis, knee joint breadth gives higher body mass estimates than femoral head breadth in australopith samples, including AL 288-1, but not early Homo samples. Body mass estimated from femoral head size in the Gona pelvis also appears low relative to its bi-iliac breadth, and results in a very short stature estimated from reverse regressions of stature on body mass and bi-iliac breadth in modern humans. Consideration of all of these factors suggests that a correction factor on the order of a 20% increase may be necessary when using femoral head size to estimate body mass in australopiths. Application of this correction to available fossil hominin specimens results in slightly different temporal trends in body mass, with more continuity between australopiths and early Homo, although there is still a significant increase in body mass in Homo, particularly after 1.5 Ma.