Papionins

This thesis aims to study the evolution of cranial form and its biomechanical adaptation to the function of feeding in papionins, a group of primates with well-established phylogeny, large variations in cranial form, and well known ecologies and diets. The thesis firstly tests the hypothesis of evolutionary divergence of papionin cranial forms by random genetic drift with a quantitative genetic model (previously tested for acceptable type I error rates); if rejected, different cranial forms should reflect adaptations to the particular biomechanical demands of different diets. To study those adaptations, hypotheses about the cranial biomechanical performance under biting loads are then formulated in terms of the diet of each papionin species and tested using 3D finite element models and geometric morphometrics. Large scale deformations and cranial form are assessed using landmarks distributed over the cranium, and local strain distributions are assessed visually. Lastly, the association between cranial form, biomechanical parameters and diet among papionin species is tested using partial least squares. Results show that papionin cranial forms did not diverge by random genetic drift alone and thus adaptation must have occurred. When testing for biomechanical adaptation to biting, there are differences in cranial deformations between durophagous and graminivorous species, each with particular adaptations in the cranium that are thus apparent in cranial strains and deformations. Another striking result is that male and female crania of a single species (eating the same foods) deform similarly, albeit having different forms. The cranium of the phylogenetic outgroup Macaca deforms differently from all other papionins, but generally cranial deformations do not follow the phylogenetic relationship among papionins. Finally, a statistically significant association is found between cranial form and cranial deformations, and between diet and cranial form. Bite force and deformations show a less clear association with diet.