River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant river dolphins are placed in two superfamilies, Platanistoidea and Inioidea. They comprise the extant families Platanistidae, Iniidae and Pontoporiidae. There are five extant species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade Cetartiodactyla, with even-toed ungulates, and their closest living relatives the hippopotamuses, from which they diverged about 40 million years ago. Specific types of Dolphins can be pink.
Iniidae is a family of river dolphins containing one living genus, Inia, and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.
Eobalaenoptera is an extinct genus of baleen whale belonging to Balaenopteroidea.
Obinautilus is an extinct genus of shelled cephalopod that has been variously identified as an argonautid octopod or a nautilid. It is known from the Late Oligocene to Pliocene of Japan. The shell is discoidal and very involute, with rapidly expanding and compressed whorls, fine radial ribs, a rounded venter with a shallow furrow, and almost closed umbilicus.
Brygmophyseter, known as the biting sperm whale, is an extinct genus of toothed whale in the sperm whale family with one species, B. shigensis. When it was first described in 1994, the species was placed in the genus Scaldicetus based on tooth morphology, but this was later revised in 1995. In 2006, it was classified into the genus Naganocetus, which is considered to be a junior synonym. The only known specimen, a nearly complete skeleton, was dated to be around 14–15 million years old. Brygmophyseter is thought to have been 7 meters (23 ft) long, and it probably had 11 or 12 teeth in the upper and lower jaws. Brygmophyseter is part of a group of macroraptorial sperm whales which tended to be apex predators using their large teeth to catch struggling prey such as whales. It had a spermaceti organ which was probably used for biosonar like in the modern sperm whale. The whale has made an appearance on The History Channel's TV series Jurassic Fight Club.
Kentriodontidae is an extinct family of odontocete whales related to modern dolphins. The Kentriodontidae lived from the Oligocene to the Pliocene before going extinct.
Livyatan is an extinct genus of macroraptorial sperm whale containing one species: L. melvillei. The genus name was inspired by the biblical sea monster Leviathan, and the species name by Herman Melville, the author of the famous novel Moby-Dick about a white bull sperm whale. It is mainly known from the Pisco Formation of Peru during the Tortonian stage of the Miocene epoch, about 9.9–8.9 million years ago (mya); however, isolated teeth from other locations such as Chile, Argentina, South Africa, and Australia implies that either it or a close relative survived into the Pliocene, around 5 mya, and was present throughout the Southern Hemisphere. It was a member of a group of hyper-predatory macroraptorial sperm whales and was likely an apex predator, preying on whales, seals, and so forth. Characteristic of raptorial sperm whales, Livyatan had functional, enamel-coated teeth on the upper and lower jaws, as well as several adaptations for hunting large prey.
Orcinus citoniensis is an extinct species of killer whale identified in the Late Pliocene of Italy and the Early Pleistocene of England. It was smaller than the modern killer whale, 4 m (13 ft) versus 7 to 10 m, and had around 8 more teeth in its jaw. It may have resembled the modern killer whale in appearance, and could represent a transitional species between the modern killer whale and other dolphins. O. citoniensis may have hunted large fish and squid in pods, and coexisted with other large predators of the time such as the orcinine Hemisyntrachelus and the extinct shark Otodus megalodon.
Acer latahense is an extinct maple species in the family Sapindaceae described from series of isolated fossil leaves. The species is known from the latest early to middle Miocene sediments exposed in the states of Oregon and Washington, USA. It is one of several extinct species placed in the living section Macrantha.
Huaridelphis is an extinct genus of river dolphins from the Early Miocene. The type species is H. raimondii, found in the Chilcatay Formation of the Pisco Basin.
Eionaletherium is an extinct genus of ground sloth from the Late Miocene coasts of Venezuela containing one species: E. tanycnemius.
Liolithax is an extinct genus of dolphin from the Middle Miocene (Serravallian) Temblor Formation of California.
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 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.
Archaeodobenus is an extinct genus of pinniped that lived during the Late Miocene of what is now Japan. It belonged to the Odobenidae family, which is today only represented by the walrus, but was much more diverse in the past, containing at least 16 genera. Unlike the modern walrus, Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like a sea lion.
Archaeophocaena teshioensis is a species of extinct porpoise from the Late Miocene 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 and Pterophocaena, 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.
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 mio for the Miocene, and phocaena for "porpoise"; the species name honors the discoverer, Takanobu Nishino. Miophocaena resides in a clade with Archaeophocaena discovered in the same area, and, along with Pterophocaena, represents an intermediate phase between porpoises and dolphins.
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 one of the oldest species discovered, after the Middle Miocene Loxolithax 16–14.8 mya and the Late Miocene Salumiphocaena 12.6–9 mya. The holotype specimen comprises a partial skeleton. The genus name derives from Ancient Greek pteryx, "wing," in reference to its unusually pronounced beak, and Latin phocaena, "porpoise." The species name honors the discoverer of the holotype, Takanobu Nishino.
Danuvius guggenmosi is an extinct species of great ape that lived 11.6 million years ago during the Middle–Late Miocene in southern Germany. It is the sole member of the genus Danuvius. The area at this time was probably a woodland with a seasonal climate. A male specimen was estimated to have weighed about 31 kg (68 lb), and two females 17 and 19 kg. Both genus and species were described in November 2019.
Ankylorhiza 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.
Stenasodelphis is an extinct genus of pontoporiid dolphin from the mid-late Miocene epoch. Its name roughly translates to "the narrow-nosed dolphin." The genus is currently monotypic, containing only the species S. russellae. The specific epithet honors Mrs. Jean Hopper, who discovered the holotype. It was found in material derived from zone 22-23 of St. Marys Formation, which dates to the early Tortonian.
