An eared seal, otariid, or otary is any member of the

marine mammal Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...

family Otariidae, one of three groupings of pinnipeds. They comprise 15

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

in seven

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

(another species became extinct in the 1950s) and are commonly known either as sea lions or

fur seal Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than Earless seal, true seals, and share with them external ears (Pinna (anatomy ...

s, distinct from true seals (phocids) and the walrus ( odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

and Southern Oceans, the southern Indian, and

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

Oceans. They are conspicuously absent in the north Atlantic. The words "otariid" and "otary" come from the Greek ' meaning "little ear", referring to the small but visible external ear flaps ( pinnae), which distinguishes them from the phocids. Otaria fg02

Evolution and taxonomy

Morphological and molecular evidence supports a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

origin of pinnipeds, sharing a common ancestor with

Musteloidea Musteloidea is a superfamily (taxonomy), superfamily of carnivoran mammals united by shared characteristics of the skull and teeth. Musteloids are the sister group of pinnipeds, the group which includes seals. Musteloidea comprises the following ...

, though an earlier hypothesis suggested that Otаriidae are descended from a

common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonl ...

most closely related to modern

bear Bears are carnivoran mammals of the family (biology), family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats ...

s. Debate remains as to whether the phocids diverged from the otariids before or after the walrus. Otariids arose in the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

(15–17 million years ago) in the North Pacific, diversifying rapidly into the Southern Hemisphere, where most species now live. The earliest known fossil otariid is '' Eotaria crypta'' from southern California, while the genus ''Callorhinus'' ( northern fur seal) has the oldest fossil record of any living otariid, extending to the middle Pliocene. It probably arose from the extinct fur seal genus '' Thalassoleon''. Traditionally, otariids had been subdivided into the fur seal (Arctocephalinae) and sea lion (Otariinae) subfamilies, with the major distinction between them being the presence of a thick underfur layer in the former. Under this categorization, the fur seals comprised two genera: ''Callorhinus'' in the North Pacific with a single representative, the northern fur seal (''C. ursinus''), and eight species in the Southern Hemisphere under the genus ''Arctocephalus''; while the sea lions comprise five species under five genera. Recent analyses of the genetic evidence suggests that ''Callorhinus ursinus'' is in fact more closely related to several sea lion species. Furthermore, many of the Otariinae appear to be more

phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

distinct than previously assumed; for example, the Japanese sea lion (''Zalophus japonicus'') is now considered a separate species, rather than a subspecies of the

California sea lion The California sea lion (''Zalophus californianus'') is a coastal eared seal native to western North America. It is one of six species of sea lions. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of Califo ...

(''Zalophus californius''). In light of this evidence, the subfamily separation has been removed entirely and the family Otariidae has been organized into seven genera with 16 species and two subspecies. Nonetheless, because of morphological and behavioral similarities among the "fur seals" and "sea lions", these remain useful categories when discussing differences between groups of species. Compared to sea lions, fur seals are generally smaller, exhibit greater

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

, eat smaller prey and go on longer foraging trips; and, of course, there is the contrast between the coarse short sea lion hair and the fur seal's fur.

Anatomy and appearance

Otariids have proportionately much larger foreflippers and pectoral muscles than phocids, and have the ability to turn their hind limbs forward and walk on all fours, making them far more maneuverable on land. They are generally considered to be less adapted to an aquatic lifestyle, since they breed primarily on land and haul out more frequently than true seals. However, they can attain higher bursts of speed and have greater maneuverability in the water. Their swimming power derives from the use of flippers more so than the sinuous whole-body movements typical of phocids and walruses. Otariids are further distinguished by a more dog-like head, sharp, well-developed canines, and the aforementioned visible external pinnae. Their postcanine teeth are generally simple and conical in shape. The dental formula for eared seals is: . Sea lions are covered with coarse guard hairs, while fur seals have a thick underfur, which has historically made them the objects of commercial exploitation. Male otariids range in size from the Galápagos fur seal, smallest of all otariids, to the over 1,000-kg (2,200-lb) Steller sea lion. Mature male otariids weigh two to six times as much as females, with proportionately larger heads, necks, and chests, making them the most

sexually dimorphic Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

of all mammals.

Behavior

All otariids breed on land during well-defined breeding seasons. Except for the

Australian sea lion The Australian sea lion (''Neophoca cinerea''), also known as the Australian sea-lion or Australian sealion, is a species of sea lion that is the only endemic pinniped in Australia. It is currently Monotypic taxon, monotypic in the genus ''Neopho ...

, which has an atypical 17.5 month breeding cycle, they form strictly annual aggregations on beaches or rocky substrates, often on islands. All species are polygynous; i.e. successful males breed with several females. In most species, males arrive at breeding sites first and establish and maintain territories through vocal and visual displays and occasional fighting. Females typically arrive on shore a day or so before giving birth. While considered social animals, no permanent hierarchies or statuses are established on the colonies. The extent to which males control females or territories varies between species. Thus, the northern fur seal and the South American sea lion tend to herd specific

harem A harem is a domestic space that is reserved for the women of the house in a Muslim family. A harem may house a man's wife or wives, their pre-pubescent male children, unmarried daughters, female domestic Domestic worker, servants, and other un ...

-associated females, occasionally injuring them, while the Steller sea lion and the New Zealand sea lion control spatial territories, but do not generally interfere with the movement of the females. Female New Zealand sea lions are the only otariids that move up to into forests to protect their pups during the breeding season. Otariids are carnivorous, feeding on

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

and

krill Krill ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...

. Sea lions tend to feed closer to shore in

upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted sur ...

zones, feeding on larger fish, while the smaller fur seals tend to take longer, offshore foraging trips and can subsist on large numbers of smaller prey items. They are visual feeders. Some females are capable of dives of up to .

Species

Family Otariidae * Subfamily Arctocephalinae (fur seals) ** Genus '' Arctocephalus'' ***

Brown fur seal The brown fur seal (''Arctocephalus pusillus''), also known as the Cape fur seal, and Afro-Australian fur seal, is a species of fur seal. Description The brown fur seal is the largest and most robust member of the fur seals. It has a large an ...

, ''A. pusillus'' ****South African fur seal, ''A. pusillus pusillus'' ****Australian fur seal, ''A. pusillus doriferus'' *** Antarctic fur seal, ''A. gazella'' *** Guadalupe fur seal, ''A. townsendi'' *** Juan Fernández fur seal, ''A. philippii'' *** Galápagos fur seal, ''A. galapagoensis'' *** New Zealand fur seal (or southern fur seal), ''A. forsteri'' *** Subantarctic fur seal, ''A. tropicalis'' *** South American fur seal, ''A. australis'' **Genus '' Callorhinus'' *** Northern fur seal, ''C. ursinus'' * Subfamily Otariinae (sea lions) ** Genus '' Eumetopias'' *** Steller sea lion, ''E. jubatus'' ** Genus '' Neophoca'' ***

, ''N. cinerea'' ** Genus '' Otaria'' *** South American sea lion, ''O. flavescens'' ** Genus '' Phocarctos'' *** New Zealand sea lion (or Hooker's sea lion), ''P. hookeri'' ** Genus ''

Zalophus ''Zalophus'' is a genus of the family Otariidae (sea lions and fur seals) of the order Carnivora. Description The seals of the genus ''Zalophus'' present a striking sexual dimorphism, since the adult males have a pronounced sagittal crest, and ...

'' ***

, ''Z. californianus'' *** † Japanese sea lion, ''Z. japonicus'' –

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

(1970s)''Zalophus californianus japonicus'' (CR)
Red Data Book, Japan Integrated Biodiversity Information System, Ministry of the Environment (Japan). "The Japanese sea lion (''Zalophus californianus japonicus'') was common in the past around the coast of the Japanese Archipelago, but declined rapidly after the 1930s from overhunting and increased competition with commercial fisheries. The last record in Japan was a juvenile, captured in 1974 off the coast of Rebun Island, northern Hokkaido." *** Galápagos sea lion, ''Z. wollebaeki'' Although the two subfamilies of otariids, the Otariinae (sea lions) and Arctocephalinae (fur seals), are still widely used, recent molecular studies have demonstrated that they may be invalid. Instead, they suggest three

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s within the family; one consisting of the northern sea lions (''Eumetopias'' and ''Zalophus''), one of the northern fur seal (''Callorhinus'') and its extinct relatives, and the third of all the remaining Southern Hemisphere species.

References

External links