Mammals are warm blooded vertebrates that have hair, breathe air, live birth, and are cared for by and receive milk from the mother. The marine mammals are classified within several. These include: order Cetacea; order Carnivora, suborder Pinnipedia; order Carnivora; and Sirenia.

Cetaceans are the whales, dolphins, and porpoises. There are about 80 different species, all of which have a completely aquatic way of life. This order is comprised of two main groups—baleen and toothed.

Baleen is a series of flexible keratin plates that hang from the upper jaw of a whale. Baleen whales feed on plankton and small animals. To feed, the whale opens its jaw and water enters its mouth. The whale then pushes the water out through the baleen and the krill and plankton get trapped in the baleen. The whale then uses its tongue to wipe off and eat the plankton. Examples of baleen whales include the blue whale, finback whale, humpback whale, and right whale.

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Toothed whales, including dolphins & porpoises have peglike teeth for catching larger animals such as fish, squid, and seals. Toothed whales are smaller than baleen whales. The sperm whale is the largest toothed whale; the narwhal is the smallest toothed whale.

Dolphins have a long beak and conical teeth. Porpoises have no beak and spatulate teeth, but researchers are now referring to both as porpoises. Killer whales are large dolphins that eat prey on squid to porpoises. Contrary to their popular name, killer whales are gentle and affectionate.

The suborder Pinnipedia includes “feather-footed” marine mammals such as seals, sea lions, and walruses. These animals are not completely aquatic; they come ashore each year to mate and bear young. The major difference between sea lions and seals is that sea lions have external ear flaps and seals do not. The walrus inhabits the Arctic and sub-Arctic marine environments. Walruses have tusks which they use to dig up mollusks, haul-out on ice, and for dominance (among males). They feed mostly on benthic mollusks and other invertebrates, which they locate with their sensitive whiskers. Like all carnivores, seals, sea lions, and walruses have sharp teeth they use for eating.

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The order Carnivora includes the sea otter. The sea otter is the smallest of all marine mammals and the most aquatic member of the weasel family. Sea otters live in kelp beds along the coast from Alaska to California. They feed on sea urchins and abalone, which they open by smashing against a rock held against their stomachs while floating on its back. They have no blubber, but have very thick fur.

Sirenians, specifically the manatee, inhabit warm coastal waters. Manatees, or sea cows, feed on vegetation in the shallow rivers and coastal waters of Florida, Caribbean, and the Amazon River. They use their upper prehensile lip to grasp vegetation while moving slowly through the water. Manatees are endangered. There are fewer than 1000 manatees left in Florida waters. The name Sirenians refers to mermaids, as sailors once took these slow moving mammals to be mermaids.

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Marine have several adaptations which allow them to live in the world oceans. Their bodies are streamlined, which allow them to swim quickly and efficiently in the water. Their modified arms or flippers are used for stabilization and steering. The blubber under their skin is used for insulation and energy.

Marine mammals also demonstrate a diving response called shunting. The blood that contains food and oxygen is isolated from the rest of the body and restricted to the vital organs. The heart rate also slows down as blood is shunted because there is less blood circulating around the body. This slowing helps to conserve the animal’s energy and oxygen.

Diving mammals also have another oxygen-binding protein, called myoglobin, located in the muscles. Together, the hemoglobin and myoglobin increase the oxygen-carrying capacity of the body. In addition, elastic tissue in the lungs and chest permits greater lung expansion during inhalation, and enables more complete and rapid inhalations and exhalations between dives.