The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits offshore Antarctic and sub-Antarctic waters. This is one of very few species to be considered completely Antarctic, as it lives in Arctic waters and no where else. It is commonly seen from ships crossing the Drake Passage, but has a circumpolar distribution.

Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the Globicephalinae. Delphinidae is a family within the superfamily Delphinoidea, which also includes the porpoises (Phocoenidae) and the Monodontidae. River dolphins are relatives of the Delphinoidea.