Awadelphis

Awadelphis hirayamai is a species of extinct oceanic river dolphin discovered in the Senhata Formation of Japan dating around 6 million years ago (mya). The genus name derives from Awa, an ancient name for the Chiba Prefecture where the holotype specimen was collected, and Ancient Greek delphis meaning "dolphin"; the species name honors the discoverer of the holotype, Ren Hirayama. It may have inhabited a subpolar environment. Awadelphis and other river dolphins of the Late Miocene may have been in abundance due to the decline of competing ancient dolphins and porpoises.