A new tillodont from the early Middle Eocene of Japan and its implication to the subfamily Trogosinae (Tillodontia : Mammalia)

概要

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A new large tillodont, represented by a fragmentary right mandible with M/2-3, was found in the upper part of the Akasaki Formation, the early Middle Eocene of Japan. It is the first record of the order Tillodontia in Japan, and is described as a new genus and species, Higotherium hypsodon, of the subfamily Trogosinae. It resembles the North American forms Trogosus and Tillodon in size; however it apparently differs from those and Kuanchuanius from China in having more hypsodont molars with well developed cusps. In detailed comparison with other trogosine molars, this new tillodont is one of the most derived taxa of the order, and morphologically situated in between the above three genera and the genus Chungchienia known from China, which was recently reassigned to the order. Morphological differences among these genera, including Higotherium hypsodon, indicate that the new taxon shows a closer relationship with Chungchienia than with North American genera, and that the rapid evolutionary diversification of the Trogosinae occurred before and during the Middle Eocene.
日本古生物学会の論文
1998-04-30