Some nonhuman primates have the capacity for head molding at birth

Cranial sutures have a changing role through ontogeny. They function as passive growth sites during active brain growth; after brain growth they may serve to dissipate biomechanical forces. A third function at the newborn stage allows mobility of these flexible, fibrous joints as a compensatory means to facilitate parturition. This is most discussed in the context of human parturition, and the apparent dilemma of passing a proportionally large fetus through the constraints of the female pelvis. To test the hypothesis that nonhuman primates also have flexible calvarial joints, we examined a sample of 34 newborn nonhuman primate skulls (including 27 New World monkeys and seven strepsirrhines) using microCT and/or histology. At least some newborns in all species studied have up to four fontanelles. Of all calvarial sutures, the sagittal is the most widely patent in all species. At least some strepsirrhines and anthropoids have widely patent sutures in the region of pterion, which may offer pliability of wide-set orbits at birth. Our findings suggest that the potential importance of fontanelles and widely patent sutures to head molding in nonhuman primates has been underestimated. Furthermore, we show that the degree of suture patency, especially in conjunction with anterior fontanelles, creates the potential for significantly more flexibility at precisely the widest transverse dimension of the neurocranium, the peak biparietal width.