Facial growth in Cercocebus torquatus: an application of three-dimensional geometric morphometric techniques to the study of morphological variation

This paper presents a study of 3-dimensional growth in the facial skeleton of the mangabey, Cercocebus torquatus. The pattern of facial cortical remodelling in this species is already well mapped from an earlier study. In this paper we consider the extent to which these remodelling maps relate to ontogenetic changes in size and shape of the face. This study is based on 31 facial landmarks taken from 49 adult and subadult faces. Our analysis draws on some of the tools of geometric morphometrics and we take this opportunity to describe our implementation of these tools for 3D data. The geometric analysis permits the known remodelling maps to be interpreted in the context of the general pattern of facial growth in this species. We are also able to examine sexual dimorphism in the face of this species and consider the extent to which males and females share similar ontogenetic allometries. Our findings indicate that the general pattern of size-related shape variation during facial growth is more or less identical for males and females up to eruption of the third permanent maxillary molar (M3). After this, ontogenetic allometries appear to diverge. The finding of a common growth allometry that is well approximated for younger specimens by a simple linear model is consistent with the earlier findings of a consistent pattern of facial remodelling up to M3 eruption. We consider the implications of these findings in terms of the potential for these approaches in the study of comparative growth in related species.