Patterns of growth of the mandibular corpus in spotted hyenas (Crocuta crocuta) and cougars (Puma concolor)

Differences in jaw morphology among adult carnivorans are well established, but the ontogenetic mechanisms by which these differences arise are largely unexplored. Mandibular ontogeny in Crocuta crocuta and Puma concolor is analysed biomechanically using principles of beam theory. In each species, the development of cross-sectional properties of the mandibular corpus associated with rigidity under loading follows a biphasic pattern of growth. In early postnatal growth, deposition of cortical bone appears to be constrained by the overall weaker tissue with which juvenile skeletons are constructed and by the need to volumelrically accommodate the developing teeth within their bony crypts. Thus, this stage of growth is characterized by a net periosteal deposition of bone and a swelling of the medullary cavity. In late postnatal growth, the constraints on endosteal deposition of bone are relieved as the permanent teeth erupt; thus, cortical thicknesses increase sharply by periosteal expansion as well as medullary contraction. Finally, it is noted that basic differences in jaw construction between Crocuta and Puma appear to develop prenatally as they are largely in place at birth. Hence, postnatal development enhances, but does not soley contribute to, the biomechanical differences in the jaws of these species.