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 Urotrichus talpoides and Dymecodon 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.