For a long time there was compelling
phylogenetic molecular evidence that the genus
Lagenorhynchus is
polyphyletic, in that it contained several species that are not closely related. found that
white-beaked and
Atlantic white-sided dolphins are phylogenetically isolated within the
Delphinidae, where they are believed to be rather
basal members of the family, along with the
orca (subfamily
Orcininae). This was confirmed in 2025 by Galatius, et al. As a result, in 2025 most of the species previously placed in
Lagenorhynchus were moved to other genera, leaving it as a monotypic genus containing only the white-beaked dolphin. Other species previously included in
Lagenorhynchus were moved to: This signal is also used by porpoises (
Phocoenidae) and the pygmy sperm whales (
Kogiidae), but is not found among other dolphins. According to , Peale's dolphin, and the other
Cephalorhynchus species, are the only dolphins that do not "whistle"; presumably, this would be the case for
hourglass dolphins, as well. Peale's dolphin also shares with several
Cephalorhynchus species the possession of a distinct white marking behind the pectoral (“armpit”) fin. The
melon-headed whale was first classified as member of the genus
Lagenorhynchus, but was later moved to its own genus,
Peponocephala. ==Notes==