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Abstract <p>The structure of the second upper molar (M2) of brown bears (<i>Ursus arctos</i>) and polar bears (<i>U.&#xa0;maritimus</i>) was studied, with nine polymorphic characters identified and their descriptions given. A west-to-east geographic pattern was discovered in the variability of the lingual cingulum of M2 in continental <i>U.&#xa0;arctos</i>. In populations of <i>U. arctos</i> on Hokkaido Island, there is likewise a decrease in the talon of M2 observed from west to east. In general, M2 in brown and polar bears is a rather variable tooth. The brown bear can be reliably differentiated from the polar bear based on the structure of M2 based on six characters. Changes in the structure of M2 in <i>U. maritimus</i> are associated with the transition to myophagy. The tooth is smaller, first of all losing its secondary elements and reducing the pressing surface due to the talon. <i>Ursus maritimus</i> has the largest number of progressive features among ancient and modern members of the genus <i>Ursus</i>. In evolutionary terms, the variability of M2 in members of the genus appears to be quite high, reflecting the main phylogenetic directions<i>.</i></p>

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Morphotype Characteristics of the Second Upper Molar (M2) of the Brown Bear (Ursus arctos) and the Polar Bear (Ursus maritimus) (Carnivora, Ursidae)

  • 期刊论文

  • 发表日期：

    2025年8月26日

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  • D. O. Gimranov

摘要

Abstract

The structure of the second upper molar (M2) of brown bears (Ursus arctos) and polar bears (U. maritimus) was studied, with nine polymorphic characters identified and their descriptions given. A west-to-east geographic pattern was discovered in the variability of the lingual cingulum of M2 in continental U. arctos. In populations of U. arctos on Hokkaido Island, there is likewise a decrease in the talon of M2 observed from west to east. In general, M2 in brown and polar bears is a rather variable tooth. The brown bear can be reliably differentiated from the polar bear based on the structure of M2 based on six characters. Changes in the structure of M2 in U. maritimus are associated with the transition to myophagy. The tooth is smaller, first of all losing its secondary elements and reducing the pressing surface due to the talon. Ursus maritimus has the largest number of progressive features among ancient and modern members of the genus Ursus. In evolutionary terms, the variability of M2 in members of the genus appears to be quite high, reflecting the main phylogenetic directions.