“True seals” (family Phocidae): Harbor seals and gray seals are both species of “true seals;” they have no external ear flap and swim by paddling with their webbed hind flippers. When on land, true seals cannot turn their back flippers underneath their pelvis, so they “hump” along on their bellies (one seal researcher’s team decided the best term for this motion was “scrunching”). The largest of the true seals is the Southern elephant seal, a species in which the males can read 20 feet in length and 8,800 pounds. The smallest of the true seals is the Baikal seal, similar to a harbor seal, which is 4.5 feet long and just 200 pounds. True seals are found in all the oceans of the world except the Indian Ocean.

“Eared seals” (family Otariidae): Sea lions and fur seals are “eared seals.” They have a small external flap by their ears and swim primarily by paddling their large foreflippers. On land, they can turn their hind flippers under their pelvis and “walk.” Eared seals are less dramatic in their size range than the true seals, though the differences are still significant. In the Steller’s sea lion, the largest of the group, males are 10 feet long and up to 2,200 pounds (females are less than half that). At 5 feet long and 150 pounds (for males), the Galapagos fur seal is the smallest member of this family. There are no eared seals in the North Atlantic, though they are plentiful elsewhere, including in the North Pacific.

Walrus (the sole member of the family Odobenidae ): There are three subspecies of walrus. Walrus have elements in common with both true and eared seals. Like eared seals, they can “walk,” and like true seals they have no external ear flaps. Of course, their most distinguishing characteristic is their tusks! Both males and females have tusks, although they are larger in the males. Walrus are also unique in that they have very little fur. Scientists are in disagreement today about whether walruses are more closely related to Phocids or Otariids. Walrus are only found in the northern hemisphere.