J. Zool., Lond. (2004) 263, 41–54 C  2004 The Zoological Society of London Printed in the United Kingdom DOI:10.1017/S0952836904004856 Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae) Tyson Sacco* and BlaireVan Valkenburgh Department of Organismic Biology, Ecology, and Evolution, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, CA 90095-1606, U.S.A. (Accepted 21 October 2003) Abstract 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. Key words: Ursidae, ecomorphology, dentition, bear, diet INTRODUCTION The family Ursidae is today represented by eight species distributed worldwide (excluding Africa, Antarctica and Australia) with diets that vary from highly carnivorous to predominately herbivorous or insectivorous. However, most ursids can be considered opportunistic omnivores, consuming vegetation, fruits, arthropods, small and large vertebrates and carrion according to availability. Three extant ursids have relatively specialized diets. The polar bear Ursus maritimus is a hypercarnivore, preying almost exclusively on seals (Smith, 1980; Stirling, 1988; Rugh & Sheldon, 1993). The giant panda Ailuropoda melanoleuca is a herbivore, existing on a diet of bamboo (Schaller et al., 1985, 1989). The sloth bear Ursus melursus is an insectivore, feeding mainly on termites and ants (Joshi, ∗ All correspondence to: Dr T. Sacco, Department of Biomedical Sciences, Cornell University, 209 Stimson Hall, Ithaca, NY 14853, U.S.A. E-mail: tws1@cornell.edu Garshelis & Smith, 1997). A fourth species, the brown bear Ursus arctos, has carnivorous tendencies, at least in some parts of its range (Craighead & Mitchell, 1982; Boertje et al., 1988; Clarkson & Liepins, 1993). Previous research has shown that craniodental morphology can predict aspects of diet in many large carnivorans (Van Valkenburgh, 1989). However, the few ursids studied have failed to exhibit the same pattern of ecomorphological relationships as other members of the order Carnivora (Van Valkenburgh, 1989). This suggests that bear morphology may be less tightly constrained by ecological requirements than the morphology of other carnivorans. Are all ursids simply so large and powerful that they do not require the craniodental specializations for specific diets we see in other members of the order Carnivora? Do ursids’ specialized diets simply represent more particular tastes, or do some bears exhibit characteristic sets of craniodental specializations for their unusual diets? Are dietary differences reflected in morphology or are all bears ‘equipped’ similarly, with