Eared seal

Eared seals, which belong to the family Otariidae, are one of the three main groups of pinnipeds, alongside true seals (phocids) and walruses (odobenids). This family includes 15 living species spread across seven genera, plus one species that went extinct in the 1950s. They are commonly called sea lions or fur seals. These animals lead a semiaquatic life: they feed and travel in the water, but come ashore or onto ice to breed and rest. Their range covers subpolar, temperate, and equatorial waters of the Pacific, Southern, southern Indian, and southern Atlantic Oceans, though they are notably missing from the North Atlantic.

The terms "otariid" and "otary" come from the Ancient Greek word ὠτάριον (ōtárion), meaning "little ear," a reference to the small, visible external ear flaps (pinnae) that set them apart from phocids.

**Evolution and taxonomy**

Both morphological and molecular evidence point to a single evolutionary origin for pinnipeds, with a common ancestor shared with the Musteloidea group. An older hypothesis suggested otariids descended from an ancestor closely related to modern bears. It is still debated whether phocids split off from otariids before or after the walrus lineage did.

Otariids first appeared in the Miocene epoch, about 15 to 17 million years ago, in the North Pacific. They then diversified rapidly into the Southern Hemisphere, where most species live today. The oldest known fossil otariid is *Eotaria crypta* from southern California. The genus *Callorhinus* (the northern fur seal) has the oldest fossil record among living otariids, dating back to the middle Pliocene, and likely evolved from the extinct fur seal genus *Thalassoleon*.

Traditionally, otariids were divided into two subfamilies: fur seals (Arctocephalinae) and sea lions (Otariinae). The main difference was that fur seals have a thick underfur layer. Under this system, fur seals included two genera: *Callorhinus* (with one species, the northern fur seal, *C. ursinus*) in the North Pacific, and eight Southern Hemisphere species under *Arctocephalus*. Sea lions comprised five species across five genera. However, molecular studies do not support this traditional split. For instance, *Callorhinus* is usually placed as an early branch off the otariid family tree, not as a close relative of the southern fur seals (*Arctocephalus*). Also, many sea lion species appear to be more genetically distinct than once thought; the Japanese sea lion (*Zalophus japonicus*), for example, is now considered a separate species rather than a subspecies of the California sea lion (*Zalophus californius*). Because of this evidence, the subfamily division has been dropped entirely, and the family Otariidae is now organized into seven genera with 16 species and two subspecies.

Still, the terms "fur seal" and "sea lion" remain useful for describing groups based on physical and behavioral similarities. Compared to sea lions, fur seals are generally smaller, show greater size differences between males and females, eat smaller prey, and take longer foraging trips. Their fur also differs: sea lions have coarse, short guard hairs, while fur seals have a dense underfur.

**Anatomy**

Otariids have much larger front flippers and stronger chest muscles than true seals (phocids). They can also rotate their hind limbs forward to walk on all fours, making them far more agile on land. They are generally considered less adapted to a fully aquatic life than phocids, since they breed mainly on land and haul out more often. In the water, however, they can reach higher speeds and are more maneuverable. They swim by using their flippers rather than the side-to-side body movements typical of phocids and walruses.

Other distinguishing features include a more dog-like head, sharp, well-developed canine teeth, and the visible external ear flaps. Their postcanine teeth are usually simple and conical. The dental formula for eared seals is 3.1.4.1-32.1.4.1. Sea lions are covered with coarse guard hairs, while fur seals have a thick underfur that historically made them targets for commercial hunting.

Male otariids range in size from the 70 kg (150 lb) Galápagos fur seal, the smallest of the family, to the over 1,000 kg (2,200 lb) Steller sea lion. Mature males weigh two to six times as much as females and have proportionally larger heads, necks, and chests, making them the most sexually dimorphic of all mammals.

**Behavior**

All otariids breed on land during clearly defined breeding seasons. With the exception of the Australian sea lion, which has an unusual 17.5-month breeding cycle, they form strictly annual gatherings on beaches or rocky surfaces, often on islands. Every species is polygynous—successful males mate with multiple females. In most species, males arrive at breeding sites first, where they establish and defend territories through vocalizations, visual displays, and occasional fights. Females usually come ashore a day or so before giving birth. Although otariids are social animals, no permanent hierarchies or statuses are set within the colonies. How much control males have over females or territories varies by species. For example, northern fur seals and South American sea lions tend to herd specific females into harems, sometimes injuring them, while Steller sea lions and New Zealand sea lions control spatial territories but generally do not interfere with female movement. Female New Zealand sea lions are the only otariids that travel up to 2 km (1.2 mi) into forests.