抄録
Geologic age of the Fortipecten takahashii (Yokoyama)-bearing lower part of the Horokaoshirarika Formation in the Ebishima area, Numata-cho, central Hokkaido, is assigned to the Neodenticula kamtschatica-Nilzschia rolandii Subzone (NPD7Ba) based on the diatom assemblage. The first occurrence age of F. takahashii in this area is estimated at 6.4-6.2 Ma and regarded as the oldest record of the species. On the other hand, the youngest record of F. takahashii is considered to be the occurrence from the early Pleistocene Yuchi Formation in northern Hokkaido. Thus, the geologic range of F. takahashii is estimated to be about five million years.
