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At first glance, especially to the untrained eye, it is hard to see any difference between seals and sea lions. Although these two animals look similar, however, there are big differences in their physical composition, social organization and even in their familial classification.
Despite their appearance, the two animals are not very closely related to one another. Seals are from the family Phocidae, while sea lions are from the family Otariidae. Sea lions are more closely related to walruses, even though it is far easier to differentiate the two by simply looking at them.
One of the biggest physical differences between sea lions and seals are their ears. In fact, as members of the order Pinniped, to which they both belong, they are termed either true seals or eared seals. Sea lions, the eared seals, have external ear flaps located on either side of their head covering the actual opening of the ear. Seals, on the other hand, do not have ear flaps. They have tiny holes on either side of their head through which they hear, but that are barely visible without close inspection.
Another major difference is in their flippers. Sea lions have large front flippers that help balance their heavy bodies. They also have back flippers that they can easily rotate when they are on land. These enable them to walk somewhat gracefully. Seals have far smaller front flippers that do not offer leverage or balance. Their rear flippers do not rotate, rendering them unable to walk gracefully on land at all. Rather, when they are out of the water, seals have to slither along in an extremely awkward manner.
The last and most significant difference between these animals is their social organization. Sea lions are gregarious and prefer to live in large groups usually of the same sex. Males and females tend to enjoy each other’s company most during mating season, beginning in early June. Seals are not as social, although females tend to gather in groups during mating season to protect themselves from competitive males looking to mate.