marine mammal material marine mammal A mammal that is primarily ocean-dwelling or depends on the ocean for its food. Mammals originally evolved on land, but later marine mammals evolved to live back in the ocean. There are five groups of marine mammals: (1) Order Sirenia: the manatee, dugong, and sea cow. (2) Order Carnivora, family Ursidae: the polar bear. (3) Order Carnivora, infrafamily Pinnipedia: the seal, sea lion, and walrus. (4) Order Carnivora, family Mustelidae: the Sea Otter and Marine Otter. (5) Order Cetacea: the whale, dolphin, and porpoise. WIKIPEDIA:Marine_mammal cetacea mammal requires discussion