The word "pinniped" means fin- or flipper-footed and refers to the marine mammals that have front and rear flippers. This group includes seals, sea lions and walruses -- animals that live in the ocean but are able to come on land for long periods of time.
Millions of years ago, the ancestors of pinnipeds lived on land. These were probably weasel- or bear-like animals that spent more and more time in the ocean and eventually adapted to this marine environment.
Pinnipeds are separated into three groups: earless seals, eared seals and walruses.
Sometimes referred to as earless seals or true seals, marine mammals in the phocid family can be easily identified by looking at their ears and flippers. They have ear holes but no external ear flaps.
They also have small front flippers and move on land by flopping along on their bellies, a movement called "galumphing." At sea, true seals move their rear flippers back and forth like a fish tail to propel themselves through the water.
Sea lions and fur seals are part of the otariid family and are sometimes referred to as eared seals. You can recognize these animals by their flippers and ears.
Unlike true seals, otariids have external ear flaps. Their front flippers are large, and on land they are able to bring all four flippers underneath their bodies and walk on them. In the water, they swim using their front flippers like oars.
Fur seals, in spite of having the word “seal” in their name, are actually closely related to sea lions. They have longer flippers than sea lions, along with a luxuriant coat of fur that was so prized by hunters that it brought them to the brink of extinction in the 19th century.
Walruses are in a family of their own called the odobenids. Both males and females have tusks and vacuum-like mouths for sucking up shellfish from the ocean floor. They have air sacs in their neck that can inflate to allow them to float as if they are wearing life preservers.
Walruses are one of the largest pinnipeds, with males reaching over 3,000 pounds. They live in the North Atlantic and Pacific oceans, in the arctic region. Walruses are protected under U.S. and Canadian laws, but limited hunting by the Inuit people is allowed.