Sea lions can walk on all fours, and true seals cannot
Look for the ears. Sea lions and fur seals have small visible ear flaps, and they can swing their hind flippers forward to walk on land. Males can outweigh females sixfold, making this family, the eared seals, the most size-unequal between sexes of any mammals on Earth.
Eared seals, or otariids, make up one of the three pinniped families, alongside true seals and the walrus. There are 15 living species in seven genera; another died out in the 1950s. The name comes from the Greek for little ear. They feed and travel at sea but breed and rest on land or ice, across the Pacific and Southern Oceans and the southern Indian and Atlantic Oceans.
Their build explains their style. Big fore-flippers and chest muscles power them through the water with bursts of speed and sharp turns, rather than the full-body undulation used by true seals. The same limbs let them clamber about on shore far more easily. They also have dog-like heads and well-developed canine teeth. Compared with true seals they are considered somewhat less committed to ocean life, since they breed on land and haul out more often.
The family arose in the North Pacific some 15 to 17 million years ago and spread south, where most species now live; the oldest known fossil, Eotaria crypta, comes from southern California. Biologists long divided the group into fur seals, with dense underfur, and sea lions, with coarse guard hairs. Molecular studies do not support that split, though the labels remain handy: fur seals tend to be smaller, more dimorphic and to make longer offshore trips for smaller prey. That luxurious underfur is also why fur seals were hunted commercially.
Males range from about 70 kilograms in the Galápagos fur seal to more than 1,000 in the Steller sea lion. Every species breeds on land in set seasons, and all are polygynous: males usually arrive first and hold territories with calls, displays and occasional fights, while females come ashore a day or so before giving birth. The Australian sea lion is the odd one out, with a breeding cycle of 17.5 months. All are carnivores, eating fish, squid and krill.
Source: Eared seal
