Lagenorhynchus is agenus ofoceanic dolphins in the infraorderCetacea, presently containing six extant species.[3] However, there is consistent molecular evidence that the genus ispolyphyletic[4] and several of the species are likely to be moved to other genera. In addition, the extinct speciesLagenorhynchus harmatuki is also classified in this genus.[5]
The nameLagenorhynchus derives from theGreeklagenos meaning "bottle" andrhynchus meaning "beak". Indeed, the "bottle-nose" is a characteristic of this genus. However, the dolphins popularly calledbottlenose dolphins belong in the genusTursiops.
The remaining four species in the genusLagenorhynchus—thePacific white-sided dolphin,Peale's dolphin,hourglass dolphin and thedusky dolphin—are consistently placed within theLissodelphininaesubfamily, in studies of molecular phylogeny,[8][4] together with theright whale dolphin and the four species of the genusCephalorhynchus (includingHector's dolphin). Some authors have suggested these four species be placed in the resurrected genusSagmatias.[6][4] However, other molecular studies place the hourglass and Peale's dolphins, phylogenetically, within the genusCephalorhynchus and do not agree with inclusion in a new genus (together with Pacific white-sided dolphin and dusky dolphin).[8]
This phylogeny is supported by acoustic and morphological data; both the hourglass and Peale's dolphins share, with the other species ofCephalorhynchus, a distinctive type ofecholocation signal known as a narrow-band/high-frequency signal.[9][10] This signal is also used by porpoises (Phocoenidae) and the pygmy sperm whales (Kogiidae), but is not found among other dolphins. According toSchevill & Watkins 1971, Peale's dolphin, and the otherCephalorhynchus species, are the only dolphins that do not "whistle"; presumably, this would be the case forhourglass dolphins, as well. Peale's dolphin also shares with severalCephalorhynchus species the possession of a distinct white marking behind the pectoral (“armpit”) fin.[citation needed]
Themelon-headed whale was first classified as member of the genusLagenorhynchus, but was later moved to its own genus,Peponocephala.[11]
^Nishiwaki, M. and K.S. Norris (1966). "A new genus,Peponocephala, for the odontocete cetacean species (Electra electra)".The Scientific Reports of the Whales Research Institute.20:95–100.
