ИСТИНА

Interpretation of differences in craniofacial form among fossil hominins rests on understanding developmental transformations; how these relate to evolutionary modifications. Many recent studies of primates have shown that a significant proportion of the differences among adult facial skeletons of different species are already established by birth, with subsequent, approximately, linear postnatal ontogenetic shape trajectories until adolescence (Cobb and O’Higgins, 2004; Mitteroecker et al., 2004; Singleton et al., 2010). Further differences in shape emerge through relative truncation or extension of ontogenetic trajecto ries. The functional matrix hypothesis (Moss & Salentijn., 1969 a,b) posits strains as orchestrating and integrating craniofacial growth in size and development in shape, through their effects on surface remodelling, and bony deposition at sutures. Does the finding of consistency of facial ontogenetic shape trajectories from morphometrics mean that bone strains in the facial skeleton are also consistent in distribution and magnitude at different ages? In the present study we explore cranial mechanical performance under masticatory loading, comparing an adult and a juvenile Macaca fascicularis. Finite Element (FE) models of these crania were built and their performance during 100N bites was compared in terms of local strains and strain contour maps. During three different simulated unilateral bites, the strain contour maps are very similar within both models, when compared to differences among bites within the same model. Peak strain magnitudes in the adult during each bite are smaller than in the juvenile, as might be expected given the difference in size. As such, relative but not absolute strain magnitudes among facial regions remain approximately constant between models. This relative invariance with age in strain distributions is consistent with the approximate linearity of facial ontogenetic trajectories noted in morphometric studies. As such these findings correspond with expectations from the functional matrix hypothesis. This study has examined only two individuals but it points the way for future research, using larger samples, to examine the links between strains, growth and development of craniofacial form. In turn the knowledge gained from such studies will be relevant to explaining the transformations in hominin craniofacial morphology during evolution.