Geometric morphometrics in paleoanthropology: Mandibular shape variation, allometry, and the evolution of modern human skull morphology

Abstract

Twenty 3D landmarks were digitized on adult mandibles from Atapuerca, Sima de los Huesos (AT-SH) (N=8), Neanderthals (N=17) and modern humans (N=82). The 3D data was converted into 2D data for Thin-Plate splines analyses. Multivariate regression of partial warps and uniform component scores on size and bootstrap analyses were used to test three hypotheses of allometry. The mandible was divided into a supra- and infra-alveolar part, which are developmentally distinct components. Separate analyses for each component revealed that all species displayed greater allometric variation at the supra-alveolar unit than at the infra-alveolar unit. The infra-alveolar unit showed allometric variation patterns associated to spatial position of the mandible within the craniofacial system. In the supra-alveolar unit the formation of a retromolar space was identified as positive allometric effect in all three species. However, this effect was morphologically different and stronger in Neanderthals and AT-SH hominids than in humans. These findings are discussed in the framework of possible evolutionary modifications of the overall skull design.