''Archaeophocaena teshioensis'' is a species of extinct

porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...

from the

Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

Koetoi Formation of Japan living around 6.4–5.5 million years ago (mya). The holotype specimen comprises a partial skull. The animal, along with ''

Miophocaena ''Miophocaena nishinoi'' is an extinct species of porpoise from the Late Miocene Koetoi Formation of Japan, dating to around 6.4–5.5 million years ago (mya), represented by a partial skull. the genus name derives from Ancient Greek ...

'' and ''

Pterophocaena ''Pterophocaena nishinoi'' is an extinct species of porpoise discovered in the Late Miocene Wakkanai Formation of Japan dating to 9.3–9.2 million years ago (mya), and may represent an intermediate phase between porpoises and dolphins. It is o ...

'', seem to represent an intermediary phase between porpoises and dolphins. The genus name derives from Ancient Greek ''archaeo'', "ancient," and Latin ''phocaena'', "porpoise"; the species name honors the Teshio District where the holotype was discovered.

References

Porpoises Mammals described in 2012 Pliocene mammals of Asia {{paleo-whale-stub