Abstract
Yabepecten ogasawarai sp. nov. is proposed from the Hongô Formation in Yamagata Prefecture, northeastern Honshû, Japan. Its occurrence is inferred to be of early late to middle late Miocene age, which makes Y. ogasawarai sp. nov. the oldest Yabepecten in the northwestern Pacific. Yabepecten was derived from Patinopecten in the northeastern Pacific, and migrated into the northwestern Pacific by the early late Miocene. From the early late Miocene onward, Yabepecten followed different evolutionary histories on both sides of the North Pacific. Yabepecten became extinct in the northeastern Pacific by the end of the early late Miocene. However, Yabepecten flourished in the northwestern Pacific from the late Pliocene to early Pleistocene, only becoming extinct at the beginning of the middle Pleistocene, along with many other species of the Omma-Manganji Fauna.
