Seal , carnivorous marine mammal that has fins as feet. The various forms, known also as fur seals, hair seals, elephant seals, sea lions, and leopard seals, are widely distributed throughout the marine regions of the frigid and temperate zones; only the monk seals are tropical. Representatives of three families of seals exist: the eared seals, walrus, and the true seals. All three families represent a reversion to aquatic habitat from ancestral land dwellers; they have become almost perfectly adapted to life in the water and resort to shores or ice floes only to breed and to rear their young. Seals eat fish, shellfish, and other marine animals .