Two Rare Warm-water Bivalves from the Pliocene Seguchi Formation in Nagano Prefecture, Central Japan

Abstract

Fossils of Divalucina soyoae Habe, 1952 and Cardilia semisulcata (Lamarck, 1819) have been recovered from a shallow-water assemblage of the upper Pliocene Seguchi Formation in Nagano Prefecture. The fossils mark the second oldest record of Divalucina soyoae and the oldest one of Cardilia semisulcata. The oldest fossil record of both species are from the Japan Sea side of Japan, not from the Pacific. Although both species live now in warm waters around Japan, Divalucina soyoae has not been found in the Japan Sea today. Moreover, the Pliocene occurrence of D. soyoae indicates a shallower habitat than it occupies today.