Numerical identification of teeth in Japanese shrew-moles, Urotrichus talpoides and Dymecodon pilirostris.

Numerical determination of the teeth of two species of Japanese shrew moles, Urotrichus talpoides and Dymecodon pilirostris (Talpidae, Insectivora), was based on the position of the premaxillo-maxillary suture, comparison of the dentitions of the two species with those of their relatives and the supernumerary tooth. The premaxillo-maxillary suture is situated between the fifth and sixth tooth anterior to the M1, and the fifth tooth anterior to the M1 was determined to be C both in the two species. The supernumerary tooth which appears in the gap between the third and fourth anterior to the M1 of the lower jaw of Urotrichus talpoides was considered as a relic of pdl which seems to have been lost relatively recently in the evolution of this species. It was also shown that the first premolar of the upper jaw of the Urotrichus talpoides and the first premolars of the Dymecodon pilirostris are dihyodont. Retention of the dihyodont first premolars in these species seems to be a primitive character and is significant in determining the phylogenetical positions of these species.