Dusky Dolphin: Lagenorhynchus obscurus

Abstract

The stocky dusky dolphin from the Southern Hemisphere and the Pacific whitesided dolphin, Lagenorhynchus obliquidens , from the northern Pacific Ocean are considered phylogenetically closely related species despite the absence of a fossil record. Some researchers suggested that L. obliquidens could almost equally well be regarded as a subspecies of the dusky dolphin. The smallish dusky dolphin can be recognized by its short beak and the bluish black to dark gray of the dorsal field contrasting with the white belly, as well as the light gray of the thoracic patch and two-pronged flank patch. The dark lips and eye patch also stand out. The falcate dorsal fin is two-toned with a dark leading edge. Unlike in L. obliquidens , the linear dorsal flank blaze does not extend farther anteriorly than about mid-body. Heavily pigmented specimens are found off Peru and Argentina. The holotype of Delphinus fitzroy caught off Argentina from Darwin's ship, Beagle, was such a melanistic form. Various cases of anomalous, piebald pigmentation are probably equivalent to so-called partial albinism.