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 returned most long-beaked populations to Delphinus delphis, retaining a separate Indo-Pacific species.
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.