Shark teeth from the upper Cretaceous Nakaminato Group in Hitachinaka, Ibaraki Prefecture, Japan

Abstract

 The Nakaminato Group (Upper Cretaceous, Campanian-Maastrichtian), which is exposed along the Pacific coast in Hitachinaka, Ibaraki Prefecture, central Japan, yields a variety of animal fossils such as ammonoids, bivalves, reptiles, etc. Here we report seven newly collected fossil shark teeth, including Carcharias cf. gracilis, cf. Carcharias sp., and cf. Squalicorax sp. In Japan, the Campanian-Maastrichtian shark teeth have been known from the Yezo, Nemuro, and Izumi Groups. However, Carcharias was not reported from the Campanian-Maastrichtian deposit in Japan. Squalicorax was known from the Izumi Group in southwestern Japan. On the other hand, this genus has not been reported from the Yezo and Nemuro Groups in Hokkaido of northern Japan. The new specimens from the Nakaminato Group suggest that these large predatory sharks, Carcharias and Squalicorax, might have co-existed in the western North Pacific Ocean during the Campanian-Maastrichtian.