Dolphins are a widely distributed and diverse group of
fully aquatic marine mammals. They are an
informal grouping within the order Cetacea,
excluding whales and porpoises, so to zoologists the grouping is paraphyletic. The dolphins comprise the extant families Delphinidae, Platanistidae, Iniidae, and Pontoporiidae. There are
40 extant species of dolphins. Dolphins, alongside other cetaceans. Source
