Humeral Length Allometry in African Hominids (sensu lato) with Special Reference to A.L. 288-1 and Liang Bua 1.

Abstract

We have previously argued that the femora of A.L. 288-1 (“Lucy,” referred to Australopithecus afarensis) and Liang Bua (LB) 1 (holotype of Homo floresiensis) have lengths near those expected for modern humans of their diminutive size. Jungers has argued that these same fossil hominins have humeri that are close in length to those expected for modern humans of their diminutive size. Yet the humero : femoral indices of these two fossil hominins are radi-cally different (5 to 6 standard deviations) from the modern human mean. These findings are seemingly contradic-tory. We investigate bivariate humeral length allometry for A.L. 288-1, LB1, and the three extant African hominid (sensu lato) genera. Results show considerable overlap in bivariate space among Homo, Pan, and (female) Gorillaindividuals in humeral length relative to body mass. However, despite this overlap, humeral length allometry var-ies greatly among the taxa, showing slight positive allometry to isometry in Homo, while showing strong negative allometry in Pan and Gorilla. Ordinary least-squares and reduced major axis regression lines of human humeral length on body mass1/3 lie near, but more often fall below, the observed humeral lengths of A.L. 288-1 and LB1, in-dicating that these fossil hominins have slightly longer humeri than would be expected for humans of their small size. In terms of femoral length, A.L. 288-1 and LB1 had somewhat shorter femora than expected for a human of their small size. This combination of slightly longer humeri and somewhat shorter femora than modern humans accounts for these specimens’ high humero : femoral indices.