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Marine mammals are mammals that have adapted to life in the ocean. Marine mammals have all the characteristics of mammals, yet they are distinctive in their appearance and survival strategies. Learning to identify marine mammals is made easier by learning their scientific classification or taxonomy.

Order Carnivora includes five families of marine mammals:

Three of the families within the order are called “pinnipeds” which means “flipper-footed”. Pinnipeds regularly come out on land to rest, breed, and give birth and are comprised of the following three families:

Family Otariidae: sea lions and fur seals have visible external ears and can walk on all four flippers by rotating their rear flippers forward under their body. They are more mobile on land than true seals and are often seen in zoos and aquariums. Their swimming power comes from their large front flippers. In California, this family includes the California sea lions, Steller sea lions, northern fur seals, and Guadalupe fur seals.

Family Phocidae: true seals have no external ears and crawl on land because their front flippers are small and their hind flippers cannot rotate forward. Their swimming power comes from their large, fan-like rear flippers. In California, this family includes Pacific harbor seals and northern elephant seals.

Family Odobenidae: walruses are distinctive for their two long tusks. Walruses inhabit the Arctic seas and ice floes. They have no external ears, but can rotate their hind flippers and walk on land. They are set apart from other pinnipeds not only by their tusks, but also by the presence of two large air pouches, or sacs, extending from each side the pharynx (in the neck). These pouches can be inflated to hold the head above water when sleeping or used as resonance chambers to enhance underwater sound.

The other marine mammals in Order Carnivora are sea otters and polar bears.  They can be referred to as "fissipeds," meaning paw or pad-footed.

Family Mustelidae:  sea otters are the only marine member of the mustelid family, which includes land mammals such as river otters, weasels, and badgers.  Sea otters are the smallest marine mammals.  They do not inhabit the open ocean, but instead live among coastal kelp beds, where they dive and hunt for a variety of shellfish and marine invertebrates.  With their exceptionally thick, dark fur, longer tail, lack of true flippers, and their ability to use a rock as a feeding tool, sea otters are easily distinguished from other marine mammals.  Sea otters are found off the central coast of California and in Washington, British Columbia, Canada, Alaska, and Russia.

Family Ursidae: Polar bears are designated as marine mammals because they depend on the ocean for a majority of their food. Thus, they are protected under marine mammal protection laws. Polar bears range throughout the Arctic regions, including parts of Alaska and Canada.

Order Cetacea includes the whales, dolphins, and porpoises: 

All species are completely aquatic, and they cannot survive on land. They have two front flippers, and their tails are uniquely shaped into two horizontal extensions, called flukes, which provide tremendous swimming power.  There are two suborders of cetaceans:

Suborder Odontoceti:  toothed whales are highly variable in body shape and size and include dolphins, porpoises, narwhal, beluga, beaked, and sperm whales.  Toothed whales have variable numbers of teeth, or may have no functional teeth at all, and breathe through a single blowhole.

Suborder Mysticeti:  baleen whales include blue, gray, humpback, and bowhead whales. Instead of teeth, baleen whales have rows of strong, closely spaced baleen plates along both sides of their upper jaws.  These plates filter out and trap small fish and plankton, which the whale then swallows. Baleen whales breathe though a pair of blowholes.

Order Sirenia includes the dugongs and manatees. 

All species live in warm or tropical waters and feed on plants.  In the U.S., manatees are found in areas of coastal Florida.  Another species of sirenian, called the Steller sea cow, once inhabited Arctic waters, but was hunted to extinction by 1768 within 27 years of its discovery.

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