History of the Paleogene molluscan fauna of Japan: a paleobiogeographic approach

Abstract

There were three biogeographic provinces in Japan, Sakhalin, and Taiwan during Paleogene time: Taiwan-South Japan, Central Japan, and North Japan-Western Okhotsk Provinces. In the middle Eocene, tropical or subtropical Tethyan Indo-Pacific elements migrated northward to southern and northern Japan. The Central Japan Province was formed by the southward migration of the Asagai-Poronaian molluscs of the North Japan-Western Okhotsk Province. In addition, the Asagai-Poronaian molluscs of the North Japan-Western Okhotsk (and Central Japan) Provinces migrated southward to Kyushu, Southern Japan, which are found in the Ashiya fauna of late early Oligocene to earliest Miocene age. Furthermore, the Asagai-Poronaian molluscs survived into the Acilana tokunagai fauna (late early to early middle Miocene) of Northern and Central Japan and indicate an offshore, cold-water mud-bottom environment.