MORPHOTYPIC CHARACTERISTICS OF THE FIRST MOLAR (M1) OF THE BROWN (URSUS ARCTOS) AND POLAR (URSUS MARITIMUS) BEARS (CARNIVORA, URSIDAE)

The structure of the first upper molar (M1) of brown (Ursus arctos) and white (U. maritimus) bears was studied, with seven features of polymorphism identified, and their descriptions given. The M1 in the mainland populations of U. arctos displays no high morphological variability, whereas populations of U. arctos from Hokkaido are distinguished by a large number of rare morphotypes and a greater complexity. In general, the M1 in brown and polar bears is not a highly variable tooth character compared to the incisors and premolars. In evolutionary terms, variations in M1 structure are rather weak in the genus Ursus. The brown bear is shown to be reliably distinguished from the polar bear based on M1 structure. The polar bear teeth vary in a peculiar way that does not coincide with the traditional scenario of tooth change in hypercarnivorous predators. Ursus arctos has a large number of progressive features in the structure of the M1, while the M1 in U. maritimus combines both progressive and primitive traits, as well as some features characteristic of only this species.