Eared Seal
Encyclopedia
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
in seven genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
commonly known either as sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...
s or fur seal
Fur seal
Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...
s, distinct from true seals (phocids) and the Walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...
(odobenids). Otariids are adapted to a semi-aquatic 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 and Southern oceans and the southern Indian
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Atlantic oceans. They are conspicuously absent in the north Atlantic.
The name otariid comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
otarion meaning "little ear", referring to the small but visible external ear flaps (pinnae) which can be used to distinguish them from the phocids.
Evolution and taxonomy
Along with the Phocidae and OdobenidaeOdobenidae
Odobenidae is a family of Pinnipeds. The only living species is walrus.In the past, however, the group was much more diverse, and includes more than ten fossil genera.- Taxonomy :All genera, except Odobenus, are extinct.*Prototaria...
, the two other members of Pinnipedia, Otаriidae are descended from a common ancestor
Enaliarctos
Enaliarctos is an extinct genus of pinniped.Prior to the discovery of Puijila, the five species in the genus Enaliarctos represented the oldest known pinniped fossils, having been recovered from late Oligocene and early Miocene strata of California and Oregon.It had a short tail and developed...
most closely related to modern bear
Bear
Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern...
s. There remains debate as to whether the phocids diverged from the otariids before or after the Walrus.
Otariids arose in the late Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
(10-12 million years ago) in the North Pacific, diversifying rapidly into the Southern Hemisphere where most species now live. Callorhinus (Northern Fur Seal
Northern Fur Seal
The Northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...
) has the oldest fossil record of any extant Otariid, extending to the middle Pliocene, and probably arose from the extinct fur seal Thalassoleon
Thalassoleon
Thalassoleon is an extinct genus of large fur seal. Thalassoleon inhabited the Northern Pacific ocean in latest Miocene and early Pliocene time. Fossils of T. mexicanus are known from Baja California and southern California. T. macnallyae is known from central California, and T. inouei is known...
.
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
Molecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
suggests that the Callorhinus ursinus is in fact more closely related to several sea lion species. Furthermore, many of the Otariinae appear to be more phylogenetically distinct than previously assumed; for example, the Japanese Sea Lion
Japanese Sea Lion
The Japanese Sea Lion is thought to have become extinct in the 1970s. Prior to 2003 it was considered to be a subspecies of California Sea Lion as Zalophus californianus japonicus. However, it was subsequently reclassified as a separate species. Some taxonomists still consider it as a subspecies...
(Zalophus japonicus) is now considered a separate species, rather than a subspecies of the California Sea Lion
California Sea Lion
The California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...
(Zalophus californius). In light of this evidence, the subfamily separation has been removed entirely and the Otariidae family has been organized into seven genera with 16 species and two subspecies.
Nonetheless, because of morphological and behavioral similarity among the "fur seals" and "sea lions", these remain useful categories when discussing differences between groups of species: all fur seals have certain features in common: the fur, generally smaller sizes, farther and longer foraging trips, smaller and more abundant prey items and greater sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. And all sea lions have certain features in common, in particular their coarse, short fur, greater bulk and larger prey than fur seals. For these reasons, the distinction remains useful
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 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
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
for eared seals is: . Sea lions are covered with coarse guard hairs, while fur seals have a thick underfur, which have historically made them the objects of commercial exploitation
Seal hunting
Seal hunting, or sealing, is the personal or commercial hunting of seals. The hunt is currently practiced in five countries: Canada, where most of the world's seal hunting takes place, Namibia, the Danish region of Greenland, Norway and Russia...
.
Male otariids range in size from the 70 kg (150 lbs) Galapagos Fur Seal
Galapagos Fur Seal
The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.- Description :...
, smallest of all pinnipeds, to the over 1000 kg (2200 lbs) Steller Sea Lion. Mature male otariids weigh two to six times more than females with proportionately larger heads, necks, and chests, making them the most sexually dimorphic of all mammals.
Behavior
All otariids breed on land during well-defined breeding seasons. Except for the Australian Sea LionAustralian Sea Lion
The Australian Sea Lion , also known as the Australian Sea-lion or Australian Sealion, is a species of sea lion that breeds only on the south and west coasts of Australia...
, 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, there are no permanent hierarchies or statuses 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
South American Sea Lion
The South American sea lion , also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the Chilean, Peruvian, Uruguayan, Argentine and Southern Brazilian coasts. It is the only member of the genus Otaria...
tend to herd specific harem-associated females, occasionally injuring them, while the Steller Sea Lion and the New Zealand Sea Lion
New Zealand Sea Lion
The New Zealand Sea Lion also known as Hooker's Sea Lion or Whakahao in Māori is a species of sea lion that breeds around the coast of New Zealand's South Island and Stewart Island/Rakiura to some extent, and to a greater extent around the New Zealand Sub-Antarctic Islands, especially the Auckland...
control spatial territories but do not generally interfere with the movement of the females.
Otariids are carnivorous, feeding on fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
. Sea lions tend to feed closer to shore in upwelling
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
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 and some females are capable of dives up to 400 m (1300 ft).
Species
- SUBORDER PINNIPEDIA
- Family Otariidae
- Subfamily Arctocephalinae
- Genus Arctocephalus
- Antarctic Fur SealAntarctic Fur SealThe Antarctic fur seal is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. As its name suggests, the Antarctic fur seal is distributed in Antarctic waters. Around 95% of the world population breeds at the Island of South Georgia...
, A. gazella - Guadalupe Fur SealGuadalupe Fur SealThe Guadalupe fur seal is one of six members of the fur seal genus Arctocephalus. Sealers reduced the population to just a few dozen by the late 19th century, but the species had recovered to 10,000 in number by the late 1990s...
, A. townsendi - Juan Fernandez Fur SealJuan Fernandez Fur SealThe Juan Fernández Fur Seal is a fur seal that breeds on the Juan Fernández Islands off the coast of Chile. It is the second smallest of the otariid seal . Discovered by navigator Juan Fernández in the sixteenth century, the seals became a target for sealers in the Maritime Fur Trade era...
, A. philippii - Galapagos Fur SealGalapagos Fur SealThe Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.- Description :...
, A. galapagoensis - Brown Fur Seal, A. pusillus
- South African Fur Seal, A. pusillus pusillus
- Australian Fur Seal, A. pusillus doriferus
- New Zealand Fur SealNew Zealand Fur SealThe Australian fur seal , or New Zealand fur seal or southern fur seal, is a species of fur seal found around the south coast of Australia, the coast of the South Island of New Zealand, and some of the small islands to the south and east of there...
or Southern Fur Seal, A. forsteri - Subantarctic Fur SealSubantarctic Fur SealThe subantarctic fur seal is a fur seal found in the southern parts of the Indian and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate tropicalis specific name.- Description :The subantarctic fur seal is...
, A. tropicalis - South American Fur SealSouth American Fur SealThe South American Fur Seal is a species of fur seal that breeds on the coasts of Chile and Argentina. The total population is around 250,000....
, A. australis
- Antarctic Fur Seal
- Genus Callorhinus
- Northern Fur SealNorthern Fur SealThe Northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...
, C. ursinus
- Northern Fur Seal
- Genus Arctocephalus
- Subfamily Otariinae
- Genus Eumetopias
- Steller Sea Lion, E. jubatus
- Genus Neophoca
- Australian Sea LionAustralian Sea LionThe Australian Sea Lion , also known as the Australian Sea-lion or Australian Sealion, is a species of sea lion that breeds only on the south and west coasts of Australia...
, N. cinerea
- Australian Sea Lion
- Genus Otaria
- South American Sea LionSouth American Sea LionThe South American sea lion , also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the Chilean, Peruvian, Uruguayan, Argentine and Southern Brazilian coasts. It is the only member of the genus Otaria...
, O. flavescens
- South American Sea Lion
- Genus Phocarctos
- New Zealand Sea LionNew Zealand Sea LionThe New Zealand Sea Lion also known as Hooker's Sea Lion or Whakahao in Māori is a species of sea lion that breeds around the coast of New Zealand's South Island and Stewart Island/Rakiura to some extent, and to a greater extent around the New Zealand Sub-Antarctic Islands, especially the Auckland...
or Hooker's Sea Lion, P. hookeri
- New Zealand Sea Lion
- Genus Zalophus
- California Sea LionCalifornia Sea LionThe California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...
, Z. californianus - †Japanese Sea LionJapanese Sea LionThe Japanese Sea Lion is thought to have become extinct in the 1970s. Prior to 2003 it was considered to be a subspecies of California Sea Lion as Zalophus californianus japonicus. However, it was subsequently reclassified as a separate species. Some taxonomists still consider it as a subspecies...
, Z. japonicus - extinct (1950s) - Galapagos Sea LionGalápagos Sea LionThe Galápagos sea lion , a species of sea lion, exclusively breeds on the Galápagos Islands and – in smaller numbers – on Isla de la Plata . Being fairly social, and one of the most numerous species in the Galápagos archipelago, they are often spotted sun-bathing on sandy shores or rock groups or...
, Z. wollebaeki
- California Sea Lion
- Genus Eumetopias
- Subfamily Arctocephalinae
- Family Phocidae: true seals
- Family OdobenidaeOdobenidaeOdobenidae is a family of Pinnipeds. The only living species is walrus.In the past, however, the group was much more diverse, and includes more than ten fossil genera.- Taxonomy :All genera, except Odobenus, are extinct.*Prototaria...
: Walrus
Further reading
- Berta, A., and L. Sumich (1999) Marine Mammals: Evolutionary Biology. San Diego: Academic Press.
- Gentry, R. L (1998) Behavior and Ecology of the Northern Fur Seal. Princeton: Princeton University Press.
- Perrin, W. F., B. Würsig, and J. G. M. Thewissen (2002) Encyclopedia of Marine Mammals. San Diego: Academic Press.
- Riedman, M. (1990) The Pinnipeds: Seals, Sea Lions and Walruses. Berkeley: University of California Press.