Orcinus paleorca

Orcinus paleorca is an extinct species of Orcinus, the genus of killer whales, dated to the Early Pleistocene (Calabrian age). The holotype is a single tooth fragment found by G. Natsume in the Sanuki Formation in Kazusa Province on the Japanese island of Honshu, and the Japanese paleontologist Hikoshichiro Matsumoto described it in 1937. The conical tooth is about 5 centimetres tall as preserved, though the whole tooth may have been twice that. Like the tooth of the living orca it lacks a coat of cementum, but its root is circular rather than oval. Its teeth are larger and closer in size to the modern killer whale's than those of the older Pliocene species Orcinus citoniensis, so it could be an ancestor of Orcinus orca. The Pleistocene deposits that held it also hold other marine mammals, including the fossil false killer whale Pseudorca yokoyamai.