''Lagenorhynchus'' is a genus of oceanic dolphins 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 them ...

, presently containing six extant species. However, there is consistent molecular evidence that the genus is polyphyletic and several of the species are likely to be moved to other genera. In addition, the extinct species ''

Lagenorhynchus harmatuki ''Lagenorhynchus'' is a genus of oceanic dolphins in the infraorder Cetacea, presently containing six extant species. However, there is consistent molecular evidence that the genus is polyphyletic and several of the species are likely to be mov ...

'' is also classified in this genus.

Etymology

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 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 common ...

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 common ...

''.

Taxonomy

There is compelling evidence from molecular phylogeny that the genus ''Lagenorhynchus'' is polyphyletic, 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, where they are believed to be rather

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

members of the family Delphinidae, together with the killer whale (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, si ...

, hourglass dolphin and dusky dolphin consistently appear nested within the Lissodelphininae subfamily in studies of molecular phylogeny, together with the Right whale dolphins 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 ''Sagmatias'' was a genus of Dolphin, dolphins, defined in 1866 by Edward Drinker Cope with Peale's dolphin as type species, described as ''Sagmatias amblodon''. It has been proposed to resurrect the genus to include four species of oceanic dolph ...

''. 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 Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...

) and pygmy sperm whales (

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

), 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