how many species of river dolphin are there
River dolphin 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 accepted family of Platanistoidea.[1] 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.[2]
Porpoise Porpoises are a group of fully aquatic marine mammals that are sometimes referred to as mereswine, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). There are six extant species of porpoise. They are small toothed whales that are very closely related to oceanic dolphins. The most obvious visible difference between the two groups is that porpoises have shorter beaks and flattened, spade-shaped teeth distinct from the conical teeth of dolphins. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates, and their closest living relatives are the hippopotamuses, having diverged from them about 40 million years ago.