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{{Automatic taxobox
| image =PacificWhiteSidedDolphine.jpg
| image_width = 240px
| image_caption = ''[[Lagenorhynchus obliquidens]]''
| authority = [[John Edward Gray|Gray]], 1846
| subdivision_ranks = [[Species]]
| subdivision =
''[[white-beaked dolphin|Lagenorhynchus albirostris]]'' <br/>
''[[Atlantic white-sided dolphin|Lagenorhynchus acutus]]'' <br/>
''[[Pacific white-sided dolphin|Lagenorhynchus obliquidens]]'' <br/>
''[[dusky dolphin|Lagenorhynchus obscurus]]'' <br/>
''[[black-chinned dolphin|Lagenorhynchus australis]]'' <br/>
''[[hourglass dolphin|Lagenorhynchus cruciger]]'' <br/>
{{Extinct}}''[[Lagenorhynchus harmatuki]]''
| authority = Gray, 1846}}
'''''Lagenorhynchus''''' is a [[genus]] in the order [[Cetacea]], traditionally containing six species:
* '''[[white-beaked dolphin]]''', ''Lagenorhynchus albirostris''
* '''[[Atlantic white-sided dolphin]]''', ''Lagenorhynchus acutus''
* '''[[Pacific white-sided dolphin]]''', ''Lagenorhynchus obliquidens''
* '''[[dusky dolphin]]''', ''Lagenorhynchus obscurus''
* '''[[Peale's dolphin]]''', ''Lagenorhynchus australis''
* '''[[hourglass dolphin]]''', ''Lagenorhynchus cruciger''
The name ''Lagenorhynchus'' derives from the [[Greek language|Greek]] ''lagenos'' meaning bottle and ''rhynchus'' meaning "beak". Indeed the "bottle-nose" is a characteristic of this genus. However the dolphins that have attained the common name [[bottlenose dolphin]] belong in the genus ''[[Tursiops]]''. The [[melon-headed whale]] was once classified in this genus but was later removed to its own ''Peponocephala'' genus.
Recent [[molecular phylogeny|analysis]] of the [[mitochondrial genome|mitochondrial]] cytochrome ''b'' gene indicates that the genus ''Lagenorhynchus'', as traditionally conceived, is not a natural ([[Monophyly|monophyletic]]) group. LeDuc et al. (1999) found that the [[white-beaked dolphin|white-beaked]] and [[Atlantic white-sided dolphin|Atlantic white-sided]] dolphins were phylogenetically isolated within the [[Delphinidae]], whereas the remaining four species were members of the Lissodelphinae, a predominantly Pacific [[clade]] of dolphins also including the [[right whale dolphin]]s and the ''[[Cephalorhynchus]]'' dolphins. These findings are somewhat problematic [[Taxonomy|taxonomically]], since the white-beaked dolphin is the [[type species]] of the genus ''Lagenorhynchus''; if the other species are not closely related to the white-beaked dolphin, then they must be removed from the genus. Accordingly, LeDuc et al. suggested that the Atlantic white-sided dolphin be placed within its own genus, ''Leucopleurus'', and that the remaining species would need taxonomic revision as well. Ledouc proposed ''[[Sagmatias]]'' as the new genus for the [[Pacific white-sided dolphin]], [[Peale's dolphin]], [[hourglass dolphin]] and [[dusky dolphin]].<ref name=leduc>{{cite journal|title=Phylogenetic Relationships among the Delphinid Cetaceans Based on Full Cytochrome B Sequences|url=http://www3.interscience.wiley.com/journal/119937779/abstract|author=Leduc, R.; Perrin, W.; Dizon, E.|date=August 18, 1998|journal=Marine Mammal Science|volume=15|issue=3|pages=619–648|doi=10.1111/j.1748-7692.1999.tb00833.x|accessdate=2008-10-05}}</ref>
May-Collado & Agnarsson (2006) actually recovered the [[hourglass dolphin|hourglass]] and [[Peale's dolphin|Peale's]] dolphins as nested phylogenetically among the species of ''Cephalorhynchus'', and they suggest that these two species be transferred to that genus. There is some acoustic and morphological support for this arrangement. Both [[hourglass dolphin|hourglass]] and [[Peale's dolphin|Peale's]] dolphin share with the species of ''Cephalorhynchus'' a distinct type of echolocation signal known as a narrow-band high-frequency signal<ref>Tougaard,J. & Kyhn, L. A. (2010) Echolocation sounds of hourglass dolphins (Lagenorhynchus cruciger) are similar to the narrow band high-frequency echolocation sounds of the dolphin genus Cephalorhynchus. Marine Mammal Science 26, 239-245.</ref><ref>Kyhn,L.A., Jensen, F. H., Beedholm, K., Tougaard, J., Hansen, M. & Madsen, P. T. (2010) Echolocation in sympatric Peale's dolphins (Lagenorhynchus australis) and Commerson's dolphins (Cephalorhynchus commersonii) producing narrow-band high-frequency clicks. Journal of Experimental Biology 213, 1940-1949.</ref>. This signal is shared with porpoises ([[Phocoenidae]]) and pygmy sperm whales ([[Kogiidae]]) but is not found among other dolphin groups. According to Schevill & Watkins (1971), Peale's dolphin and the ''Cephalorhynchus'' species are the only dolphins that do not whistle. Presumably this is the case for [[hourglass dolphin]]s as well. Peale's dolphin also shares with several ''Cephalorhynchus'' species the possession of a distinct white "armpit" marking behind the pectoral fin.
According to May-Collado & Agnarsson's analysis, the remaining two species, the [[dusky dolphin|dusky]] and [[Pacific white-sided dolphin|Pacific white-sided]] dolphins are closely related to each other and form the [[sister group]] to the (expanded) genus ''Cephalorhynchus''. If this placement is accurate, a new genus name will need to be coined to accommodate these two species.
''For further details, please see the articles on each species.''
==References==
{{Reflist}}<!--added under references heading by script-assisted edit-->
#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.
#Schevill, W.E., Watkins, W.A. (1971). Pulsed sounds of the porpoise ''Lagenorhynchus australis''. Breviora 366, 1–10.
{{Cetacea|O.}}
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