page_title: River dolphin
section_title: Classification
hierarchical_section_title: River dolphin / Taxonomy and evolution / Classification
caption_attribution_description: English: Life reconstruction of Arktocara yakataga
context_page_description: 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.
  River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow water and strong river currents. They range in size from the 5-foot long South Asian river dolphin to the 8-foot and 220-pound Amazon river dolphin. Several species exhibit sexual dimorphism, in that the males are larger than the females. They have streamlined bodies and two limbs that are modified into flippers. River dolphins use their conical-shaped teeth and long beaks to capture fast-moving prey in murky water.
context_section_description: Four families of river dolphins (Iniidae, Pontoporiidae, Lipotidae and Platanistidae) are currently recognized, comprising three superfamilies (Inioidea, Lipotoidea and Platanistoidea). Platanistidae, containing the two subspecies of South Asian river dolphin, is the only living family in the superfamily Platanistoidea. Previously, many taxonomists had assigned all river dolphins to a single family, Platanistidae, and treated the Ganges and Indus river dolphins as separate species. A December 2006 survey found no members of Lipotes vexillifer (commonly known as the baiji, or Chinese river dolphin) and declared the species functionally extinct. With their disappearance, one of the recently accepted superfamilies, Lipotoidea, has become extinct.
  The current classification of river dolphins is as follows:
  Superfamily Platanistoidea
  Family Platanistidae
  Genus Platanista
  South Asian river dolphin, Platanista gangetica, with two subspecies
  Ganges river dolphin (susu), P. g. gangetica
  Indus river dolphin (bhulan), P. g. minor
  Family †Allodelphinidae (Oligocene - Miocene)
  Family †Squalodelphinidae (Oligocene to Miocene)
  Family †Squalodontidae (Oligocene to Miocene)
  Family †Waipatiidae (Oligocene to Miocene)
  Superfamily Inioidea
  Family Iniidae
  Genus Inia
  Amazon river dolphin (boto), Inia geoffrensis
  Inia geoffrensis geoffrensis
  Inia geoffrensis humbotiana
  Araguaian river dolphin, Inia araguaiaensis
  Bolivian river dolphin, Inia boliviensis
  Genus †Meherrinia (late Miocene)
  Genus †Isthminia (Miocene)
  Family Pontoporiidae
  Genus †Auroracetus
  †Auroracetus bakerae
  Genus Pontoporia
  La Plata dolphin (Franciscana), Pontoporia blainvillei
  Superfamily (?†) Lipotoidea
  Family (?†) Lipotidae
  Genus (?†) Lipotes
  (?†) Baiji (or Chinese river dolphin), Lipotes vexillifer (possibility extinct)
  In 2012 the Society for Marine Mammalogy began considering the Bolivian (Inia geoffrensis boliviensis) and Amazonian (Inia geoffrensis geoffrensis) subspecies as full species Inia boliviensis and Inia geoffrensis, respectively; however, much of the scientific community, including the IUCN, continue to consider the Bolivian population to be a subspecies of Inia geoffrensis.
  In October 2014, the Society for Marine Mammalogy took Inia boliviensis and Inia araguaiaensis off their list of aquatic mammal species and subspecies and currently does not recognize these species-level separations.
caption: Life reconstruction of Arktocara yakataga, an allodelphinid
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