Fur seals, or Arctocephalinae make up one of the two distinct groups of marine mammals called "seals". Fur seals are usually smaller than sea lions and have a coat of dense fur intermixed with guard hairs. The guard hairs are molted once a year. They gather in large herds at mating time, when the males will aggressively defend their territories and harems. The fur seals possess bare rear flippers with small claws. They display sexual dimorphism, as the males are often more than five times heavier than the females.
Both the fur seals and the true seals are members of the Pinnipedia, which is usually regarded as a suborder of the order Carnivora but sometimes as an independent order. However, the fur seals, like their close relatives the sea lions, retain some ability to walk on land as their hind limbs can be brought forward under the body to bear the animal's weight, and retain small but visible external ears.
The fur seals plus the sea lions as a group, make up the family Otariidae, and are called eared seals or walking seals to distinguish them from the earless true seals of the family Phocidae. The fur seals alone make up the Arctocephalinae subfamily.