Evolution of hypsodonty reveals a long-standing ecological separation in the Japanese shrew-moles.

Habitat segregation has been reported for the Japanese shrew-moles by several studies. However, there is a lack of surveys aimed at characterizing the ecological separation occurring between U rotrichus talpoides and D ymecodon pilirostris. In this paper, possible reasons for this ecological separation are proposed for the first time. A geometric morphometrics analysis was performed on first lower molars and mandibles of both fossil and extant specimens. The results evidenced that U. talpoides evolved a hypsodont configuration and a more robust mandible bearing an enlarged second incisor, while D. pilirostris maintained the primitive brachyodont morphology and a slender mandible. The fossil specimens proved to be very similar to their extant relatives. The shape analyses of m1 and the mandible suggest that U . talpoides possesses a more efficient feeding behaviour compared with that of D . pilirostris. Moreover, the derived state of the mandible morphology, associated with a larger size, suggests that U . talpoides largely displaced D . pilirostris and confined it to isolated highland areas by means of competition for food resources. [ABSTRACT FROM AUTHOR]