Seals are semiaquatic marine mammals. They have four flippers, so are in a category of animals known as pinnipedia which means 'fin-footed'. The pinnipeds group contains 3 families: phocidae, the earless or true seal (eg. common seal), otaridae,eared seals (eg. fur seals and sea lions) and odobenidae (walrus). 

Pinnipeds, commonly known as seals are a widely distributed and diverse clade of carnivorous, fin footed, semiaquatic marine mammals. They comprise the extant families Odobenidae (whose only living member is the walrus), Otariidae (the eared seals: sea lions and fur seals), and Phocidae (the earless seals, or true seals). There are 33 extant species of pinnipeds, and more than 50 extinct species have been described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage (descended from one ancestral line). Pinnipeds belong to the order Carnivora and their closest living relatives are bears and musteloids (weasels, raccoons, skunks, and red pandas), having diverged about 50 million years ago.