Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae)

Patterns of morphological variation in the skulls of extant bears were studied as they relate to diet and feeding behaviour. Measurements of craniodental features were used to compute indices that reflect dietary adaptations of the dentition and biomechanical properties of the skull, jaw and related musculature. Species were classified as either carnivores, omnivores, herbivores or insectivores. Differences among dietary groups were assessed with analysis of variance and discriminant factor analysis. Results demonstrated significant morphological separation among all four groups. Carnivores were distinguished by, among other features, molar size reduction, flexible mandibles and, most surprisingly, relatively small carnassial blades. In contrast, herbivores displayed, among other features, large molar grinding areas, rigid mandibles and large carnassial blades. The insectivorous sloth bear was characterized by extreme reduction of the post-canine teeth. As expected, omnivores tended to have morphology intermediate between that of carnivorous and herbivorous ursids. Comparison with previous studies revealed that bears exhibit a different set of morphological specializations for diet than other carnivoran groups. Carnivorous ursids, for example, were found to share aspects of craniodental morphology with omnivorous canids. The relatively weak adaptations for carnivory observed in bears may be the result of selection for the ability to cope with temporal fluctuations in dietary components. The giant panda Ailuropoda melanoleuca was found to have a relatively stiff jaw and great mechanical advantage of the jaw-closing muscles, features previously observed in carnivorous canids and unexpected in this herbivorous bear. Comparison of patterns of morphological variation and patterns of phylogenetic relationships among species revealed surprisingly strong congruence between morphology and phylogenetics.