BIOGEOGRAPHY AND THE PLEISTOCENE EXTINCTION OF NEOGASTROPODS IN THE JAPAN SEA

Abstract

During the middle to late Pleistocene glacial lowstands, when the Japan Sea was almost isolated geographically, low-salinity surface water and anoxic deep water were formed. Pliocene to early Pleistocene buccinid gastropods which mainly lived deeper than the lower sublittoral zone underwent extinction owing to anoxic deep water. On the other hand, upper–sublittoral muricid and buccinid species suffered from extinction due to decrease of surface salinity. However, fossil records indicate that species in the Pacific Ocean east of Japan having shallow minimum depths reinvaded the Japan Sea through shallow, northern straits at least in the latest Pleistocene. The fossil and Recent records of two Buccinum species restricted to the Japan Sea side indicate normal salinity and oxic water at ca. 100–400 m during glacial lowstands.