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.
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.
A dolphin was on the coat of arms of the dauphin, the title given the eldest son and heir of the king of France.
Dolphins range in size from the small tucuxidolphin, which grows to about 1.2 m (4 ft) in length and weighs about 50 kg (110 lb), to the killer whale, which can grow to 9.8 m (32 ft) in length and weigh over 5,500 kg (12,100 lb).
Dolphins are commonly fl, brown, or gray in color and are often marked with patterns of white or light colors.
Freshwater species include the Ganges River (or "susu"), which is nearly blind; the largest freshwater species, the Amazon River ("boutu"); and the Irrawaddy dolphin, one of the slower swimmers.
Dolphins are small-toothed whales that migrate through the tropical and temperate oceans of the world; freshwaterdolphins live in the rivers of South America and tropical Asia.
Dolphins are born weighing 30 to 50 pounds and are 35 to 50 inches in length.
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