R & C | MAMMALOGY

Heyning, J.E. and W.F. Perrin 1994. Evidence for two species common dolphins (genus Delphinus) from the eastern North Pacific. Contributions in Science. No. 442, 35 pp. Natural History Museum of Los Angeles County.

Abstract:

Two forms of common dolphins occur sympatrically in the Southern California Bight: a long-beaked form and a short-beaked form. We re-examined the two forms based on 320 specimens, including only adults in morphometric analyses. Color pattern separates the two forms completely, as do total length and all measures of rostral length, both absolute and relative. Numerous additional features, such as vertebral count and tooth counts, show modal differences. Many of the differences in color pattern between the two forms seem to hold for other ocean basins, with some variation. Other workers have also found short- and long-beaked forms in these other regions. The levels of differences we see in this region of sympatry are equal to or greater than those for some other full species of small oceanic dolphins. Our data strongly suggest there is no gene flow between the two forms in this region of sympatry. Thus, we conclude that these two forms of common dolphins represent two distinct species. We review the nomenclature for Delphinus and provide re-descriptions of the two species. The short-beaked form is referable to Delphinus delphis Linnaeus. The long-beaked form in the eastern Pacific is the nominal species Delphinus bairdii Dall, 1873 for which we designate a neotype, although we note that this species is a junior synonym of Delphinus capensis Gray, 1828. Further work should resolve the degree of geographical variation for these two species and whether the nominal D. tropicalis is a valid species.