River dolphin

River dolphins are four species of dolphin which reside in freshwater rivers and estuarys. They are classed in the Platanistoidea superfamily of cetaceans. Three species live in fresh water rivers. The fourth species, the La Plata Dolphin, lives in saltwater estuaries and the ocean. However it is scientifically classed in the river dolphin family rather than the oceanic dolphin family.

Ecology:
River dolphins are some of the most endangered of all the world's cetaceans. Due to habitat loss, hunting by humans, and naturally low numbers, they are extremely vulnerable to extinction. Also, many river dolphins also possess very poor eyesight — some are considered blind — which can lead to unfortunate encounters with humans or manmade objects (boats or fishing nets for example).

Some dolphin species can live in marine or riverine environments. The Tucuxi, for example, is equally at home in both ecotypes. However these are not classified in the Platanistoidea superfamily and are therefore not regarded as true river dolphins.

Taxonomy:
In the most recent classification (Rice, 1998) there are four families that make up the river dolphins. Platanistidae is listed as the only extant family of the Platanistoidea superfamily. The previously accepted classification treated all four families as belonging to this superfamily and treated the Ganges and Indus River Dolphins as separate species.

Classification by Rice (1998)
Superfamily Platanistoidea
Family Platanistidae
Ganges and Indus River Dolphin Platanista gangetica
Family Iniidae
Amazon River Dolphin (or Boto) Inia geoffrensis
Family Lipotidae
Chinese River Dolphin (or Baiji) Lipotes vexillifer
Family Pontoporiidae
La Plata Dolphin (or Franciscana) Pontoporia blainvillei
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Previous classification
Superfamily Platanistoidea
Family Platanistidae
Ganges River Dolphin Platanista gangetia
Indus River Dolphin Platanista minor
Family Iniidae
Amazon River Dolphin (or Boto) Inia geoffrensis
Family Lipotidae
Chinese River Dolphin (or Baiji) Lipotes vexillifer
Family Pontoporiidae
La Plata Dolphin (or Franciscana) Pontoporia blainvillei

References:

Rice, Dale W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4.