Irrawaddy dolphin
| Irrawaddy dolphin | |
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| 1878 illustration | |
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| Size comparison to an average human | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | Delphinidae |
| Genus: | Orcaella |
| Species: | O. brevirostris |
| Binomial name | |
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Orcaella brevirostris (Owen in Gray, 1866) |
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Orcaella genus range map See: Irrawaddy dolphin geographic range map |
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The Irrawaddy dolphin (Orcaella brevirostris) is a euryhaline species of oceanic dolphin found in discontinuous subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia.
One of the earliest recorded descriptions of the Irrawaddy dolphin was by Sir Richard Owen in 1866 based on a specimen found in 1852, in the harbour of Visakhapatnam on the east coast of India. It is one of two species in its genus. It has sometimes been listed variously in a family containing just itself and in Monodontidae and in Delphinapteridae. There is now widespread agreement to list it in the family Delphinidae.
Genetically, the Irrawaddy dolphin is closely related to the killer whale (orca). It is also closely related to the Australian snubfin dolphin, and these two were only recently recognised as distinct species. The species name brevirostris comes from the Latin meaning short-beaked. In 2005, genetic analysis showed the Australian snubfin dolphin found at the coast of northern Australia forms a second species in the Orcaella genus.
Overall, the dolphins' colour is grey to dark slate blue, paler underneath, with no distinctive pattern. The dorsal fin is small and rounded behind the middle of the back. The forehead is high and rounded; the beak is lacking. The front of its snout is blunt. The flippers are broad and rounded. The species found in Borneo, the finless porpoise, Neophocaena phocaenoides, is similar and has no back fin; the humpback dolphin, Sousa chinensis, is larger, has a longer beak and a larger dorsal fin.
Vernacular names for O. brevirostris include the following:
The Irrawaddy dolphin is similar to the beluga in appearance, though most closely related to the killer whale. It has a large melon and a blunt, rounded head, and the beak is indistinct. The dorsal fin, located about two-thirds posterior along the back, is short, blunt, and triangular. The flippers are long and broad. It is lightly coloured all over, but slightly more white on the underside than the back. Unlike any other dolphin, the Irrawaddy's u-shaped blowhole is placed on the left of the midline and opens towards the front of the dolphin. Their short beaks appear very different than those of other dolphins, and their mouths are known for having 12-19 peg-like teeth on each sides of their jaws. Irrawaddys can range from 90 kg (200 lb) to 200 kg (440 lb) and length is 2.3 m (7.5 ft) at full maturity. Maximum recorded length is 2.75 m (9.0 ft) of a male from Thailand.
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