Coastal common dolphins tend to have longer beaks and more subdued colours than offshore ones, and in 1994 that difference was formalised: Delphinus delphis for the short-beaked form, Delphinus capensis for the long-beaked. The split was widely adopted in field guides and management documents.
Genetic sampling then complicated it. Long-beaked populations in the eastern Pacific, the eastern Atlantic and elsewhere turned out not to form a single lineage. Instead, similar body forms had evolved repeatedly where dolphins specialised on coastal prey. In 2016 the Society for Marine Mammalogy's taxonomy committee dropped Delphinus capensis altogether and returned every long-beaked population to Delphinus delphis; the long-beaked Indo-Pacific form is retained only as a subspecies, Delphinus delphis tropicalis.
The episode is a useful reminder that consistent physical differences are not proof of separate ancestry. It also left a paper trail: sources written between roughly 1994 and 2016 use a two-species arrangement that no longer reflects the accepted treatment.