Of arcs and vaults: the biomechanics of bone-cracking in spotted hyenas (Crocuta crocuta)

The ability to break open large bones has evolved independently in only three groups of carnivorous mammals, all of which have robust teeth, vaulted foreheads, and pronounced sagittal crests. One unusual skull feature, present in bone-cracking members of the family Hyaenidae, is a caudally elongated frontal sinus, hypothesized to function in resistance to bending and stress dissipation during bone-cracking. In the present study, we used finite element (FE) analysis to examine patterns of stress distribution in the spotted hyena (Crocuta crocuta) skull during unilateral biting, and inquire about the functional role of the fronto-parietal sinus in stress dissipation. We constructed and compared three FE models: (1) a ‘normal’ model of an adult Crocuta skull; (2) a model in which the caudal portion of the fronto-parietal sinus was filled with bone; and (3) a model in which we flattened the sagittal crest to resemble the plate-like crests of other mammals. During biting, an arc of stress extends from the bite point up through the vaulted forehead and along the sagittal crest. Our results suggest that pneumatization of the hyena's skull both enhances its ability to resist bending and, together with the vaulted forehead, plays a critical role in evenly dissipating stress away from the facial region. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 246–255.