Proa et al PeerJ Raw Data.zip

The form of the cranium can vary extensively among closely related species of papionins (Cercopithecidae, Primates), a fact that is often related to their adaptive differences to distinct diets. Yet, the form of the cranium can also vary greatly between males and females of the same species, even though both sexes tend to have the same diet. Here we use finite elements models and geometric morphometrics to test for differences in cranial biomechanical performance that could be attributed to differences in diet and feeding habits in male and female specimens of <i>Papio anubis</i> and <i>Theropithecus gelada</i>, two extant papionin species with known diets. It is expected that adaptation to that same diet must have occurred in both sexes, despite differences in form. Strain contour plots show that differences can be seen between male and female of each species, but differences between male and female <i>T. gelada </i>are much larger than those between male and female <i>P. anubis</i> for all bites. Nevertheless, larger differences in strain are seen between species, rather than between male and female of the same species. An analysis of deformations shows male and female of each species falling with each other, and away from the other species. <i>P. anubis</i> male and female deform almost identically, with the female deforming only slightly less than the male for all bites. Differences between male and female <i>T. gelada</i> are more marked, with the female deforming far less than the male particularly during incisor bites; the trajectory followed, though, is the same, with differences being mainly in magnitude of deformation. These results are an indicator that diet might have had a major adaptive effect on papionin cranial form, but they also indicate that papionin cranial form may be highly constrained by other non-masticatory functions. Also, these results highlight the difficulties in trying to interpret dietary ecology from modes and magnitudes of cranial deformation, which, being difficult in extant species with known diets and sexes, becomes extremely challenging when applied to extinct species.