WAetiocetus is a genus of extinct basal mysticete, or baleen whale that lived 33.9 to 23.03 million years ago, in the late Oligocene in the North Pacific ocean, around Japan, Mexico, and Oregon, U.S. It was first described by Douglas Emlong in 1966 and currently contains known four species, A. cotylalveus, A. polydentatus, A. tomitai, and A. weltoni. These whales are remarkable for their retention of teeth and presence of nutrient foramina, indicating that they possessed baleen. Thus, Aetiocetus represents the transition from teeth to baleen in Oligocene mysticetes. Baleen is a highly derived character, or synapomorphy, of mysticetes, and is a keratinous structure that grows from the palate, or roof of the mouth, of the whale. The presence of baleen is inferred from the fossil record in the skull of Aetiocetus. Aetiocetus is known from both sides of the Pacific Ocean: it was first documented in Oregon, United States, but it is also known from Japan and Mexico. The genus is currently constrained to the Northern hemisphere and has little value in biostratigraphic studies of the Oligocene due to its limited occurrences across the Pacific.
WAlbertocetus is an extinct genus of primitive odontocete cetacean from late Oligocene (Chattian) marine deposits in North Carolina, and belonging to the family Xenorophidae.
WAllodelphis is an extinct genus of whale belonging to Allodelphinidae found in marine deposits of the eastern North Pacific.
WAnkylorhiza is an extinct genus of dolphin 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 4.8 meters (16 ft) long, with a long, robust skull bearing conical teeth that were angled forwards at the tip of the snout.
WArktocara 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 2.26 or 2.28 meters, comparable to its closest living relative, the South Asian river dolphin, which measures 2.4 meters (7.9 ft). However, the animal probably had an elongated beak and neck, so it may have been longer. The animal is known only from a partially preserved skull. Its ecology may have been similar to the modern day Dall's porpoise, and it may have competed with contemporaneous delphinoids. Its remains were found in the Poul Creek Formation, which has also yielded several mollusk species.
WCotylocara is a genus of primitive odontocete from late Oligocene (Chattian) marine deposits of the Chandler Bridge Formation of South Carolina belonging to Xenorophidae.
WHoropeta is a genus of baleen whale from the Late Oligocene (Chattian) Kokoamu Greensand of New Zealand.
WInermorostrum is a genus of primitive odontocete from early Oligocene (Rupelian) marine deposits in South Carolina belonging to the family Xenorophidae.
WJanjucetus is an extinct genus of cetacean, and a basal baleen whale (Mysticeti), from the Late Oligocene around 25 million years ago (mya) off southeast Australia, containing one species J. hunderi. Unlike modern mysticetes, it possessed large teeth for gripping and shredding prey, and lacked baleen, and so was likely to have been a predator that captured large single prey animals rather than filter feeding. However, its teeth may have interlocked, much like those of the modern-day filter-feeding crabeater seal, which would have allowed some filter-feeding behavior. Its hunting behaviour was probably similar to the modern-day leopard seal, probably eating large fish. Like baleen whales, Janjucetus could not echolocate; however, it did have unusually large eyes, and so probably had an acute sense of vision. The only specimen was found on the Jan Juc beach, where the remains of the extinct whales Mammalodon, Prosqualodon and Waipatia have also been discovered.
WKentriodontidae is an extinct family of odontocete whales related to modern dolphins. The Kentriodontidae lived from the Oligocene to the Pliocene before going extinct.
WMammalodon is an extinct genus of archaic baleen whale belonging to the family Mammalodontidae.
WMammalodontidae is a family of extinct whales known from the Oligocene of Australia and New Zealand.
WMirocetus is a genus of archaic odontocete from the late Oligocene (Chattian) of Azerbaijan. Like many other primitive odontocetes, its classification has been fluid since its description.
WOtekaikea is an extinct genus of toothed whale closely related to Waipatia. It is known from the late Oligocene (Chattian) of New Zealand.
WPatriocetus is an extinct genus of toothed whale.
WProsqualodon is an extinct genus of Early to Middle Miocene cetacean from Argentina, Australia, New Zealand and Venezuela.
WSqualodon 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 relative is the South Asian river Dolphin.
WWaharoa is a genus of eomysticetid baleen whale from the Late Oligocene (Chattian) of New Zealand. It was identified with the discovery of Waharoa ruwhenua by Boessenecker and Fordyce (2015), which added a new genus and species to a monophyletic family Eomysticetidae.
WWaipatia is an extinct genus of whale from the late Oligocene (Chattian) of New Zealand.