''Lagenorhynchus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

oceanic dolphin Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...

s in the infraorder

Cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel th ...

, presently containing six extant species. However, there is consistent molecular evidence that the genus is

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

and several of the species are likely to be moved to other genera. In addition, the extinct species '' Lagenorhynchus harmatuki'' is also classified in this genus.

Etymology

The name ''Lagenorhynchus'' derives from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''lagenos'' meaning "bottle" and ''rhynchus'' meaning "beak". Indeed, the "bottle-nose" is a characteristic of this genus. However, the dolphins popularly called

bottlenose dolphin Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the comm ...

s belong in the genus ''

Tursiops Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the commo ...

''.

Taxonomy

There is compelling evidence from molecular phylogeny that the genus ''Lagenorhynchus'' is

, meaning that it currently contains several species that are not closely related. found that the white-beaked and Atlantic white-sided dolphins are phylogenetically isolated within the

Delphinidae Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...

, where they are believed to be rather basal members of the family

, together with the

killer whale The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white pat ...

(subfamily Orcininae). The remaining four species of ''Lagenorhynchus'': Pacific white-sided dolphin,

Peale's dolphin Peale's dolphin (''Lagenorhynchus australis'') is a small dolphin found in the waters around Tierra del Fuego at the foot of South America. It is also commonly known as the black-chinned dolphin or even Peale's black-chinned dolphin. However, s ...

, hourglass dolphin and

dusky dolphin The dusky dolphin (''Lagenorhynchus obscurus'') is a dolphin found in coastal waters in the Southern Hemisphere. Its specific epithet is Latin for "dark" or "dim". It is very closely genetically related to the Pacific white-sided dolphin, b ...

consistently appear nested within the Lissodelphininae subfamily in studies of molecular phylogeny, together with the

Right whale dolphin Right whale dolphins are cetaceans belonging to the genus ''Lissodelphis''. It contains the northern right whale dolphin (''Lissodelphis borealis'') and the southern right whale dolphin (''Lissodelphis peronii''). These cetaceans are predominan ...

s and the four species of the genus '' Cephalorhynchus'' (including Hector's dolphin). Some authors have suggested that these four species are placed in the resurrected genus '' Sagmatias''. However, other molecular studies recover the

hourglass An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand) ...

and Peale's dolphins as nested phylogenetically within the four species of ''Cephalorhynchus'' and thereby speaks against inclusion in a new genus together with Pacific white-sided dolphin and dusky dolphin. This phylogeny is supported by acoustic and morphological data. Both hourglass and Peale's dolphins share with the species of ''Cephalorhynchus'' a distinct type of echolocation signal known as a narrow-band, high-frequency signal. This signal is shared with porpoises ( Phocoenidae) and pygmy sperm whales (

Kogiidae Kogiidae is a family comprising at least two extant species of Cetacea, the pygmy (''Kogia breviceps)'' and dwarf (''K. sima)'' sperm whales. As their common names suggest, they somewhat resemble sperm whales, with squared heads and small lowe ...

), but is not found among other dolphin groups. According to , Peale's dolphin and the ''Cephalorhynchus'' species are the only dolphins that do not whistle. Presumably this is the case for hourglass dolphins, as well. Peale's dolphin also shares with several ''Cephalorhynchus'' species the possession of a distinct white "armpit" marking behind the pectoral fin. The melon-headed whale was first classified as member of the genus ''Lagenorhynchus'', but was later moved to its own genus, ''Peponocephala''.

Notes

References

* * * * * {{Taxonbar, from=Q837606 Cetacean genera Animals that use echolocation Taxa named by John Edward Gray