Lagenorhynchus
Encyclopedia
Lagenorhynchus is a genus
in the order Cetacea
, traditionally containing six species:
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 dolphin
s 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
.
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. Both hourglass
and Peale's
dolphin 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) 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
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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
in the order Cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
, traditionally containing six species:
- white-beaked dolphinWhite-beaked DolphinThe White-beaked dolphin is a marine mammal belonging to the family Delphinidae in the suborder Odontoceti .-Taxonomy:...
, Lagenorhynchus albirostris - Atlantic white-sided dolphinAtlantic White-sided DolphinThe Atlantic White-sided Dolphin is a distinctively coloured dolphin found in the cool to temperate waters of the North Atlantic Ocean.-Taxonomy:...
, Lagenorhynchus acutus - Pacific white-sided dolphinPacific White-sided DolphinThe Pacific White-sided Dolphin is a very active dolphin found in the cool to temperate waters of the North Pacific Ocean.-Taxonomy:...
, Lagenorhynchus obliquidens - dusky dolphinDusky DolphinThe dusky dolphin 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, but current scientific consensus is that they are distinct species...
, Lagenorhynchus obscurus - Peale's dolphinPeale's DolphinPeale's Dolphin 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...
, Lagenorhynchus australis - hourglass dolphinHourglass DolphinThe hourglass dolphin is a small dolphin in the family Delphinidae that inhabits Antarctic and sub-Antarctic waters....
, Lagenorhynchus cruciger
The name Lagenorhynchus derives from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
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
Bottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
belong in the genus Tursiops. The melon-headed whale
Melon-headed Whale
The melon-headed whale is a cetacean of the oceanic dolphin family . It is closely related to the pygmy killer whale and pilot whale, and collectively these dolphin species are known by the common name blackfish. It is also related to the false killer whale...
was once classified in this genus but was later removed to its own Peponocephala genus.
Recent analysis
Molecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
of the mitochondrial cytochrome b gene indicates that the genus Lagenorhynchus, as traditionally conceived, is not a natural (monophyletic
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
) group. LeDuc et al. (1999) found that the white-beaked
White-beaked Dolphin
The White-beaked dolphin is a marine mammal belonging to the family Delphinidae in the suborder Odontoceti .-Taxonomy:...
and Atlantic white-sided
Atlantic White-sided Dolphin
The Atlantic White-sided Dolphin is a distinctively coloured dolphin found in the cool to temperate waters of the North Atlantic Ocean.-Taxonomy:...
dolphins were phylogenetically isolated within the Delphinidae, whereas the remaining four species were members of the Lissodelphinae, a predominantly Pacific clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of dolphins also including the right whale dolphin
Right whale dolphin
Right whale dolphins are cetaceans belonging to the genus Lissodelphis. It contains the Northern Right Whale Dolphin and the Southern Right Whale Dolphin . These cetaceans are predominantly black, white beneath, and one of the few without a dorsal fin or ridge...
s and the Cephalorhynchus
Cephalorhynchus
Cephalorhynchus is a genus in the dolphin family Delphinidae. It consists of four species:*Commerson's Dolphin, Cephalorhyncus commersonii*Chilean Dolphin, Cephalorhyncus eutropia*Heaviside's Dolphin, Cephalorhyncus heavisidii...
dolphins. These findings are somewhat problematic taxonomically
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
, since the white-beaked dolphin is the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the 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
Sagmatias
Sagmatias is a genus that has been proposed for certain dolphin species that are currently placed in the genus Lagenorhynchus. Mitochondrial DNA studies have indicated that certain dolphin species within Lagenorhynchus are actually more closely related to dolphins within the genus Cephalorhynchus...
as the new genus for the Pacific white-sided dolphin
Pacific White-sided Dolphin
The Pacific White-sided Dolphin is a very active dolphin found in the cool to temperate waters of the North Pacific Ocean.-Taxonomy:...
, Peale's dolphin
Peale's Dolphin
Peale's Dolphin 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...
, hourglass dolphin
Hourglass Dolphin
The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits Antarctic and sub-Antarctic waters....
and dusky dolphin
Dusky Dolphin
The dusky dolphin 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, but current scientific consensus is that they are distinct species...
.
May-Collado & Agnarsson (2006) actually recovered the hourglass
Hourglass Dolphin
The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits Antarctic and sub-Antarctic waters....
and Peale's
Peale's Dolphin
Peale's Dolphin 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...
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
Hourglass Dolphin
The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits Antarctic and sub-Antarctic waters....
and Peale's
Peale's Dolphin
Peale's Dolphin 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...
dolphin 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) 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
Hourglass Dolphin
The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits Antarctic and sub-Antarctic waters....
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
Dusky Dolphin
The dusky dolphin 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, but current scientific consensus is that they are distinct species...
and Pacific white-sided
Pacific White-sided Dolphin
The Pacific White-sided Dolphin is a very active dolphin found in the cool to temperate waters of the North Pacific Ocean.-Taxonomy:...
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.