A Three-Dimensional Look at the Neanderthal Mandible

Mandibular traits that differentiate Neanderthals from modern humans include greater robusticity, a receding symphysis, a large retromolar space, a rounder gonial area, an asymmetric mandibular notch and a posteriorly positioned mental foramen in Neanderthals. These features have been shown to separate Neanderthals from modern humans in both non-metric and metric, including 3-D geometric morphometric, studies. However the degree to which these differences are related to size and function is still under discussion. The aim of this study is to further assess the effects of allometry and evaluate the influence of masticatory and paramasticatory activities on mandibular shape using a morphological integration approach. Data were collected in the form of three-dimensional coordinates of 27 landmarks, superimposed using generalized Procrustes analysis, and analyzed using canonical variates, regression and partial least squares analyses. Consistent with previous findings, Neanderthals are separated from modern human mandibles in the canonical variates analysis. However, partial least squares analysis indicates a similar pattern of integration for the two human groups, suggesting homology across modern humans and Neanderthals in the mandibular features examined. This finding does not support a paramasticatory hypothesis for Neanderthal mandibular shape, although it also does not refute this hypothesis. Finally, allometry was found to influence the expression of the retromolar gap.