Sexual dimorphism in the baboon pelvis

In many sexually dimorphic primate species, the pelvic canal is disproportionately larger in females than in males. Pelvic dimorphism has been attributed to factors such as obstetrics, phylogeny, and hormonal influences. Pelvic size is also correlated with body mass and other skeletal measurements. Larger females have larger babies; therefore, it is predicted that pelvic dimensions should be greater in larger females and more variable in males. This study uses the Bramblett Savanna Baboon Collection, a skeletal collection of wild adult Papio cynocephalus (n=28) with associated body masses to address this question. Body mass is compared with measurements of the pelvis. Since primate skeletal collections with actual body mass associations are rare, linear measurements of the clavicle, humerus, femur, and tibia and high resolution X-ray CT scans of the humeral, femoral, and tibial midshaft are analyzed as potential proxies for body mass within this taxon. This study contributes to the few studies testing correlations between body size and pelvic size. Articular surfaces of long bones and some pelvic measurements are larger when body mass is greater. However in some pelvic measurements traditionally deemed to be related to obstetrics, scaling is separated by sex. The correlations between pelvic size and body size are not significant when single proxies are used unless global skeletal variables (GSV) are applied. Furthermore in females, aspects of femoral cross-sectional morphology show sexual dimorphism and are correlated with iliac width suggesting that the relatively wider hips cause different biomechanical loadings.