Abstract
The replacement of the first premolars in the mandible and maxilla of Lesser Japanese shrew-moles, Dymecodon pilirostris, and in the maxilla of Greater Japanese shrew-moles, Urotrichus talpoides was observed by the examination of skeletal material and X-ray examination of juvenile in-dividuals. On both species of shrew-moles, the second deciduous premolars are notreplaced. Among extant metatherian and eutherian mammals, only tapirs (Tapirus) show the first premolar replacement. A mong extinct mammals, the evidence regarding the replacement of the first premolar has not been reported as yet, except for the Tapiroidea of the Pleistocene (Simpson, 1945) and the Eocene (Radinsky, 1963). Based on the generally accepted concept that the first premolar if present is not replaced in mammals, Ziegler (1971) erroneously identified the non-replaced second premolar of the Japanese shre wmoles as the “first” premolar. Accordingly, only two premolars are present between the “first” pre-molar and the molar series so that the “second” premolar is regarded to have been lost. Anterior to the “first” premolar on the maxilla are four teeth of which first three have been identified as inci-sors and last tooth as canine by Ziegler. Based on the re-examination of skeletal material, it is now clear that only two incisors are on the premaxillary bone in these shrew-moles, and that Ziegler id entified the first tooth of the tooth series on the maxilla as the third incisor. The identification given by Ziegler is antagonistic to the definition of incisors and canines.
