Oligocene cetaceans

Squalodon is an extinct genus of whales of the Oligocene and Miocene epochs, belonging to the family Squalodontidae. Named by Jean-Pierre Sylvestre de Grateloup in 1840, it was originally believed to be an iguanodontid dinosaur but has since been reclassified. The name Squalodon comes from Squalus, a genus of shark. As a result, its name means "shark tooth". Its closest modern relatives are the 2 species of the genus Platanista ( the Ganges river dolphin and Indus river dolphin).

Janjucetus is an extinct genus of baleen whale that lived during the Late Oligocene (Chattian) in south-east Australia, around 25 million years ago. Remains of the genus have been found in the Jan Juc Marl in the Jan Juc Formation near the township of the same name, and have been assigned to two species: the type species J. hunderi and J. dullardi. This locality has yielded remains of more extinct cetaceans, including Prosqualodon, Waipatia, and the related Mammalodon.

Kentriodon is an extinct genus of toothed whale related to modern-day dolphins. Fossils have been found in North America, Europe and Japan. Several species have been described.

Mammalodon is an extinct genus of archaic baleen whale belonging to the family Mammalodontidae.

Kentriodontidae is an extinct family of odontocete whales related to modern dolphins. The Kentriodontidae lived from the Oligocene to the Pliocene before going extinct.

Waipatia is an extinct genus of odontocetes from the late Oligocene (Chattian) of New Zealand.

Prosqualodon is an extinct genus of Early to Middle Miocene cetacean from Argentina, Australia, New Zealand, and Venezuela.

Mammalodontidae is a family of extinct whales known from the Oligocene of Australia and New Zealand.

Patriocetus is an extinct genus of toothed whale.

Xenorophidae is an extinct family of dolphin-like odontocetes (toothed whales) that lived in the Southeastern United States during the Oligocene. They were among the first major groups of odontocetes to diversify in the fossil record and are notable for their ability to echolocate.

Waipatiidae is an extinct family of odontocetes currently known from the Oligocene of the Pacific Ocean and possibly Europe and the Caucasus.

Otekaikea is an extinct genus of toothed whale closely related to Waipatia. It is known from the late Oligocene (Chattian) of New Zealand.

Eomysticetidae is a family of extinct mysticetes belonging to Chaeomysticeti (toothless mysticetes). It is one of two families in the basal chaeomysticete clade Eomysticetoidea (the other being Cetotheriopsidae).

Arktocara is an extinct genus of river dolphin from the Oligocene epoch of Alaska, containing one species, A. yakataga. Having been discovered in 25-million-year-old strata near the 60th parallel north, it is perhaps the oldest-known crown toothed whale and the northmost river dolphin discovered. It was a member of the now-extinct family Allodelphinidae, along with the genera Allodelphis, Goedertius, Ninjadelphis, and Zarhinocetus. It measured approximately , comparable to its closest living relative, the South Asian river dolphin, which measures . However, the animal probably had an elongated

Ankylorhiza (meaning "fused roots"; in reference to the type of dentition seen in early toothed whales) is an extinct genus of toothed whale that lived in what is now the United States during the Oligocene epoch, between 29 and 23.5 million years ago. The type and only known species is A. tiedemani, though two fossil skeletons may represent an additional, second species within the genus. Ankylorhiza was about long, with a long, robust skull bearing conical teeth that were angled forwards at the tip of the snout.

Albertocetus is an extinct genus of primitive odontocete cetacean from early Oligocene (Rupelian) marine deposits in North Carolina, and belonging to the family Xenorophidae.

Allodelphis is an extinct genus of whale belonging to Allodelphinidae found in marine deposits of the eastern North Pacific.

Allodelphinidae is a family of primitive platanistoid river dolphins found in marine deposits in the eastern North Pacific region, Alaska, and Japan.

Agorophius is an extinct genus of toothed whale that lived during the Oligocene period, approximately , in the waters off what is now South Carolina.

Yamatocetus canaliculatus is an extinct species of eomysticetid baleen whale from the Late Oligocene of Japan.

Simocetus (from simus, "pug-nosed", and cetus, "whale") is an extinct genus of toothed whale that lived during the Oligocene period, approximately , making it the oldest named toothed whale, although older unnamed toothed whales exist.

Inermorostrum is a genus of primitive odontocete from early Oligocene (Rupelian) marine deposits in South Carolina. It belongs to the family Xenorophidae.

Cotylocara is a genus of primitive odontocete from late Oligocene (Chattian) marine deposits of the Chandler Bridge Formation of South Carolina. It belongs to the Xenorophidae.

Horopeta is a genus of baleen whale from the Late Oligocene (Chattian) Kokoamu Greensand of New Zealand.