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Seals and walruses comprise a group of 33 aquatic mammal species with flippers known as pinnipeds, which is Latin for "feather-footed." Biologists group pinnipeds into three families: true seals, or phocids; sea lions and fur seals, known as otarids; and walruses, or odobenids. The walrus, of which there is only one species, found around the North Pole, has features that liken it to its true seal relatives, but it also shares traits with otarids.
With the exception of the Baikal seal, which is endemic to a freshwater lake of the same name in Russia, pinnipeds are marine creatures found around the poles and in temperate regions. Elephant seals and walruses, which can weigh up to 8,800 and 3,700 pounds, respectively, are the largest pinnipeds. All pinnipeds have streamlined bodies, sometimes likened to torpedoes, which give them better mobility in water than on land. Walruses and the overwhelming majority of seals are social animals that gather in huge numbers during breeding seasons.
Both seals and walruses have an acute sense of hearing, particularly at sea. True seals are sometimes called earless seals because they lack external ear organs, as do walruses. Otarids, on the other hand, are easily distinguished by the presence of ear flaps.
A true seal's front flippers are much smaller than those of other pinnipeds. Sea lions, fur seals and walruses can bring their hind flippers forward, under their bodies, which enables them to move on all fours on land. True seals lack this capability and must drag themselves with their front claws or flop around on their bellies. In water, true seals propel themselves by swaying their hind flippers in a fish-like manner, while walruses and otarids swim using their forelimbs.
The walrus' distinctive feature is a pair of ivory tusks, a trait unique among pinnipeds. Both male and female walruses have tusks, which are overgrown canine teeth that can be as long as 3 feet. They use their tusks in self-defense -- against predators and, in the case of males, rival walruses -- and also employ them as ice-picks to lift themselves out of the water.
All pinnipeds are carnivores. True seals, fur seals and sea lions feed mostly on fish and crustaceans. The exception is the leopard seal, a true seal that resembles the feline whose name it bears, not only in the spots on its coat, but also in its reputation as a predator; found in the waters of Antarctica, leopard seals are the only pinnipeds that eat other warm-blooded animals, such as penguins, and even other seals. The diet of walruses, on the other hand, consists mostly of shellfish, like clams and mussels, which they suck up off the ocean floor.
- The Marine Mammal Center: Pinnipeds
- Britannica Online Encyclopedia: Seal
- Britannica Online Encyclopedia: Pinniped
- Seal Conservation Society: Species Information - The Pinnipeds
- National Geographic: Walrus
- Defenders of Wildlife: Walrus
- National Geographic: Leopard Seals
- San Diego Zoo Animal Bytes: Sea Lion
- Seal Conservation Society: Baikal Seal
- National Geographic: Elephant Seals
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