|
''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 ''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 the genus ''Lagenorhynchus'', as traditionally conceived, is not a natural (monophyletic) group. 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. actually recovered the hourglass and Peale's dolphins as nested phylogenetically among the species of ''Cephalorhynchus'', and they suggest these two species be transferred to that genus. Some acoustic and morphological data support for this arrangement. 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), 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. According to an analysis by , 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. ==Notes== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lagenorhynchus」の詳細全文を読む スポンサード リンク
|