Can anyone please define sea mammals?
A marine mammal is 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: Order Sirenia: the manatee, dugong, and sea cow Order Carnivora, family Ursidae: the polar bear Order Carnivora, infrafamily Pinnipedia: the seal, sea lion, and walrus Order Carnivora, family Mustelidae: the Sea Otter and Marine Otter Order Cetacea: the whale, dolphin, and porpoise Since different groups of marine mammals originate from different ancestors, this is a case of convergent evolution. Since mammals originally evolved on land, their spines are optimized for running, allowing for up-and-down but only little sideways motion. Therefore, marine mammals typically swim by moving their spine up and down. By contrast, fish normally swim by moving their spine sideways. For this reason, fish mostly have vertical caudal (tail) fins, while marine mammals
