Mandible size and shape in extant Ursidae (Carnivora, Mammalia): a tool for taxonomy and ecogeography

The family Ursidae is currently one of the taxonomic group with the lowest number of species among Carnivora. Extant bear species exhibit broad ecological adaptations both at inter and intra specific level and taxonomic issues within this family remain unresolved (i.e. the number of recognisable subspecies). Here, we investigate a sample of bear mandibles using two-dimensional geometric morphometrics to better characterise bear taxonomy and evolution with a focus on one of the most widespread species: the brown bear (Ursus arctos). Our analyses confirm that both size and shape data are useful continuous characters that discriminate with very high percentage of accuracy extant bears. We also identify two very distinct mandibular morphologies in the subspecies Ursus actos isabellinus and Ursus arctos marsicanus. These taxa exhibit a high degree of morphological differentiation possibly as a result of a long process of isolation. Ecogeographical variation occurs among bears mandibles although climate strongly impact only macroevolutionary shape differences between tropical and temperate species.