Evolutionary implications of bite mechanics and feeding ecology in bears


P. Christiansen, Zoological Museum, Universitetsparken 15, 2100 Copenhagen Ø, Denmark. Tel: +45 35 32 10 93; Fax: +45 35 32 10 10
Email: p2christiansen@zmuc.ku.dk


Bite forces (BFs) based on a dry skull static model were computed for 122 specimens of all eight species of extant ursids. It was found that the giant panda has high BFs for its body size, and large moment arms about the temporomandibular joint, both muscle inlever moment arms and outlever moment arms to the carnassial and canine. The insectivorous sloth bear and to some extent the omnivorous black bears were the opposite. The small sun bear has very large canines and high BFs, which are not well understood, but could potentially be related to its frequent opening of tropical hardwood trees in pursuit of insects. Force profiles along the lower jaw revealed significant differences among the various species, both related to diet and inferred applied BFs. The panda is the only specialized ursid with respect to craniodental morphology and BFs, but is still unspecialized for herbivory compared with other large, herbivorous mammals, probably owing to a rather short evolutionary history, but possibly its morphology is constrained by genealogy. The low BFs in the sloth bear and its mandibular force profiles are derived for a diet of insects and fruit, requiring only low BFs and largely dorsoventral bite moments. In contrast, the unspecialized morphology and moderate BFs relative to body size of the polar bear and spectacled bear are probably also a result of a short evolutionary history.