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Orcaella
The snubfin dolphins (''Orcaella'') are a genus of Cetaceans containing two members: the Irrawaddy dolphin (''Orcaella brevirostris'') and the Australian Snubfin dolphin (''Orcaella heinsohni''). The genus was long believed to be monotypic with the only species being the Irrawaddy dolphin; however, in 2005, supposed Irrawaddy dolphin populations inhabiting the Australian/New Guinean regions were found to be significantly different and were declared a separate new species named the Australian Snubfin dolphin.
==Taxonomy and evolution==
Until 2005, ''Orcaella brevirostris'' was the only recognized species in the genus ''Orcaella.'' However, comparisons within the populations of ''Orcaella'' inhabiting the Asia region and populations inhabiting the Australia/New Guinea region show distinctions in habitat, morphology, and genetics.〔Ross, G. J. (2006). Review of the conservation status of Australia's smaller whales and dolphins. Department of the Environment and Water Resources.〕 Morphological differences include skull shape, presence or absence of a median dorsal groove in front of the dorsal fin, height of dorsal fin, and coloration. Genetic analysis constitutes a 5.9% difference between the two populations.〔Beasley, I., Robertson, K. M. and Arnold, P.. 2006. DESCRIPTION OF A NEW DOLPHIN, THE AUSTRALIAN SNUBFIN DOLPHIN ORCAELLA HEINSOHNI SP. N. (CETACEA, DELPHINIDAE). Marine Mammal Science 21: 365 -400〕 In 2005, these significant distinctions considered by Beasley, Arnold and Robertson warranted a taxonomic split of the genus ''Orcaella'' into two separate species, ''Orcaella brevirostris'' and ''Orcaella heinsohni'' . ''Orcaella brevirostris'' known as the Irrawaddy Dolphin consists of the Asian population. The newly recognized species, known as the Australian Snubfin dolphin, consists of the Australian/New Guinea population.〔Beasley, Isabel L. (2007). Conservation of the Irrawaddy dolphin, Orcaella brevirostris (Owen in Gray, 1866) in the Mekong River: biological and social considerations influencing management. PhD thesis, James Cook University.〕
The Snubfin dolphins (''Orcaella'') contain two of the 35 species of Oceanic dolphins that make up the Cetacean family of Delphinidae.〔Evans, Peter G.H. (1984). Macdonald, D., ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 180–185. ISBN 0-87196-871-1.〕 The phylogenetic status of ''Orcaella'' has long been confused. Although the Snubfin dolphins share similar external features with the Monodontidae (narwhal),〔 a genetic study conducted by Arnason and Gretarsdottir identified the 'Irrawaddy Dolphin' as a Delphinid. In their study, phylogenetic information obtained from a highly repetitive DNA (hrDNA) component characteristic of all cetaceans show that ''Orcaella'' share close relationships with the Delphinidae rather than the Monodontidae.〔Arnason U., Gretarsdottir S.. 1992. Evolution of the common cetacean highly repetitive DNA component and the systematic position of Orcaella brevirostris. Journal of Molecular Evolution 34: 201-208.〕
Recent molecular analyses indicate that the genus ''Orcaella'' is closely related to the Orca of the genus ''Orcinus'', the two of them together forming the subfamily Orcininae〔LeDuc, R.G., Perrin, W.F., Dizon, A.E. (1999). Phylogenetic relationships among the delphinid cetaceans based on full cytochrome ''b'' sequences. Marine Mammal Science 15, 619–648.〕〔May-Collado, L., Agnarsson, I. (2006). Cytochrome ''b'' and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution 38, 344-354.〕
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