Sergio Almécija

It has been proposed that the morphological differences between the distal femora of humans and early Plio-Pleistocene hominins are the result of a heterochronic shift in the human lineage towards a longer period of development. This assertion was tested using threedimensional geometric morphometric microscribe data, collected as a series of x, y, z coordinates. Data were collected on an ontogenetic sample of forty-three Pan troglodytes individuals categorized in seven age classes and twenty-seven Homo sapiens, aged 2 to adult, as well as relevant original fossils. Data were subjected to a generalized procrustes analysis and multivariate statistics were subsequently performed. The ontogenetic trajectory for Homo and Pan were significantly different. For modern humans, the major ontogenetic change in the distal femur was captured almost entirely along principal component 1 in a principal components analysis. WT 15000 and ER 1481 fell within the 95% confidence ellipse of modern humans, but all other fossils fell well outside. Major ontogenetic changes in Pan were captured on both PC 1 and PC 2. Distal femora from Australopithecus afarensis, as well as ER 1500, fell within the 95% equal frequency ellipse for the Pan ontogenetic trajectory, while ER 1481 and WT 15000 were furthest outside. These results indicate that shape differences between the distal femora of Plio-Pleistocene hominins and humans cannot be accounted for by heterochrony alone. This research was supported by WG 7515, NSF DDI 0550901, and partial funding from NSF 0333415 (NYCEP) and 0513360 (Eric Delson).