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iRiver dolphins
Ganges River DolphinPhotographer:Brian D. Smith
Ganges River Dolphin
Photographer:Brian D. Smith
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Superfamily: Platanistoidea
Families

See text

River dolphins are four species of dolphin which reside in freshwater rivers and estuaries. 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.

EcologyEdit

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.

TaxonomyEdit

In the most recent classification (Rice, 1998) there are currently four extant families that make up the river dolphins - however it is almost certain that by the end of the decade the Lipotidae will have perished, it having been declared "functionally extinct" in December 2006. Platanistidae is listed as the only existent 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) Edit

Previous classificationEdit

  • Superfamily Platanistoidea
    • Family Platanistidae
      • Ganges River Dolphin Platanista gangetica
      • Indus River Dolphin Platanista minor
    • Family Iniidae
      • Amazon River Dolphin (or Boto) Inia geoffrensis
    • Family Lipotidae
      • Chinese River Dolphin (or Baiji) Lipotes vexillifer (Presumed extinct as of 2006)
    • Family Pontoporiidae
      • La Plata Dolphin (or Franciscana) Pontoporia blainvillei

ExtinctionEdit

On Dec. 13th, 2006, the Yangtze River Dolphin, or Baiji, was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen [1]. The last verified sighting of the beak-nosed dolphin was in September of 2004. [2]

It is believed that overfishing and sub-aquatic sonar pollution (which interfered with the dolphin's sonar-based method of locating food), led to the extinction. Reuters news reported this their first record of a mammalian extinction in "50 years".

ReferencesEdit

  • Rice, Dale W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. 231 pp.



Adapted from the Wikipedia article "River dolphin" http://en.wikipedia.org/wiki/River_dolphin

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