Lagenorhynchus

Taxobox
name = "Lagenhorhynchus"

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image_width = 240px
image_caption = "Lagenorhynchus obliquidens"
regnum = Animalia
phylum = Chordata
classis = Mammalia
subclassis = Eutheria
ordo = Cetacea
subordo = Odontoceti
familia = Delphinidae
genus = "Lagenorhynchus"
genus_authority = Gray, 1846
subdivision_ranks = Species
subdivision = "Lagenorhynchus albirostris"
"Lagenorhynchus acutus"
"Lagenorhynchus obliquidens"
"Lagenorhynchus obscurus"
"Lagenorhynchus australis"
"Lagenorhynchus cruciger"

"Lagenorhynchus" is a genus in the order cetacea, traditionally containing six species:
* the White-beaked Dolphin, "Lagenorhynchus albirostris"
* the Atlantic White-sided Dolphin, "Lagenorhynchus acutus"
* the Pacific White-sided Dolphin, "Lagenorhynchus obliquidens"
* the Dusky Dolphin, "Lagenorhynchus obscurus"
* the Peale's Dolphin, "Lagenorhynchus australis"
* the Hourglass Dolphin, "Lagenorhynchus cruciger"

The name "Lagenorhynchus" derives from the 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 analysis of the mitochondrial cytochrome "b" gene indicates that the genus "Lagenorhynchus", as traditionally conceived, is not a natural (monophyletic) group. LeDuc et al. (1999) found that the White-beaked and 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 Dolphins and the "Cephalorhynchus" dolphins. These findings are somewhat problematic 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.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]

May-Collado & Agnarsson (2006) actually recovered the Hourglass and 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, at least with respect to Peale's Dolphin. According to Schevill & Watkins (1971), Peale's Dolphin and the "Cephalorhynchus" species are the only dolphins that do not whistle (no acoustic data are available for the Hourglass Dolphin). 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 and 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

#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.