For many years, the common dolphin was considered to be a single highly variable species that occupied tropical and warm temperate waters around the world. However, morphological (Heyning and Perrin 1994) and genetic (Rosel et al. 1994) research on common dolphins from the eastern Pacific documented the presence of two reproductively isolated species, the long and short beaked common dolphins. Besides the implied differences in beak length between the two species, there are also distinct differences in their cranial morphology and in their external color pattern. Similar differences exist in common dolphins in other oceans, including an Indian Ocean form that has an even longer beak than the nominal long-beaked species (Jefferson and Van Waerebeek 2002). Building upon the earlier work from the eastern Pacific, current research is attempting to determine the relationship of long and short beaked common dolphins from different parts of the world.
Chivers, S. J., R. G. LeDuc, and K. M. Robertson. 2003. A feasibility study to evaluate using molecular genetic data to study population structure of eastern North Pacific Delphinus delphis. NOAA, NMFS, Southwest Fisheries Science Center Administrative Report LJ-03-12. 14pp.
Heyning, J. E., and W. F. Perrin 1994. Evidence for two species of common dolphins (genus Delphinus) from the eastern North Pacific. Natural History Museum of Los Angeles County Contributions in Science 442:1-35.
Jefferson, T. A. and Van Waerebeek, K. 2002. The taxonomic status of the nominal dolphin species Delphinus tropicalis van Bree, 1971. Marine Mammal Science 18:787-818.
Rosel, P. E., A. E. Dizon, and J. E. Heyning. 1994. Genetic analysis of sympatric morphotypes of common dolphins (genus Delphinus). Marine Biology 119:159-167.