MORPHOTYPIC VARIABILITY OF THE INCISORS OF THE BROWN (URSUS ARCTOS) AND POLAR (URSUS MARITIMUS) BEARS (CARNWORAI URSIDAE)

摘要

The structure of both upper and lower incisors is studied in the brown (Ursus arctos) and polar (Ursus maritimus) bears, and incisor morphotypes are delimited. A description and the frequency of occurrence of each morphotype are given. The brown bear is, revealed to show a greater degree of morphotypic variability of the incisors, both upper and lower. This species is characterized by a more complex structure of the corona compared to the polar bear. A west-east trend in increasing tooth complexity is observed in U. arctos populations. Based on incisor structure, mainland brown bears somewhat differ from those from Hokkaido. Within that island, differences are noted between the western, central and eastern populations. The incisors of the polar bear are generally better adapted to carnivory than those of the brown bear. The main evolutionary trend in the development of incisors in Ursus representatives is grinding surface simplification.