Aneared seal,otariid, orotary, is any member of themarine mammal familyOtariidae, one of three groupings ofpinnipeds. They comprise 15extantspecies in sevengenera (another species became extinct in the 1950s) and are commonly known either assea lions orfur seals, distinct fromtrue seals (phocids) and thewalrus (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 thePacific andSouthern Oceans, the southernIndian, andAtlantic Oceans. They are conspicuously absent in the north Atlantic.
The words "otariid" and "otary" come from theAncient Greek ὠτάριον (ōtárion), meaning "little ear",[2] referring to the small but visible external ear flaps (pinnae), which distinguishes them from thephocids.
Morphological and molecular evidence supports amonophyletic origin of pinnipeds, sharing a common ancestor withMusteloidea,[3][4] though an earlier hypothesis suggested that Otаriidae are descended from acommon ancestor most closely related to modernbears.[5] Debate remains as to whether the phocids diverged from the otariids before or after the walrus.
Otariids arose in theMiocene (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 isEotaria crypta from southern California,[1] while the genusCallorhinus (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 genusThalassoleon.
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 genusArctocephalus; while the sea lions comprise five species under five genera.[6] Recent analyses of thegenetic evidence suggests thatCallorhinus ursinus is in fact more closely related to several sea lion species.[7] Furthermore, many of the Otariinae appear to be morephylogenetically distinct than previously assumed; for example, theJapanese sea lion (Zalophus japonicus) is now considered a separate species, rather than a subspecies of theCalifornia sea lion (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.[8][9]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 greatersexual dimorphism, 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.
Cladogram showing relationships among the otarids, combining several phylogenetic analyses. The fur seal branch has not been resolved.[10][clarification needed]
The ear flaps (pinnae) of Otariids are small yet evident
Otariids have proportionately much larger fore-flippers 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.[citation needed] 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.[citation needed]
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. Thedental 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, which has historically made them the objects of commercialexploitation.[citation needed]
Male otariids range in size from the 70 kg (150 lb)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 mostsexually dimorphic of all mammals.[11]
All otariids breed on land during well-defined breeding seasons. Except for theAustralian sea lion, which has an atypical 17.5 month breeding cycle, they form strictly annual aggregations on beaches or rocky substrates, often on islands. All species arepolygynous; 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 theSouth American sea lion tend to herd specificharem-associated females, occasionally injuring them, while the Steller sea lion and theNew 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 2 km (1.2 mi) into forests to protect their pups during the breeding season.[12][13][14][15]
Otariids are carnivorous, feeding onfish,squid andkrill. Sea lions tend to feed closer to shore inupwelling 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 400 m (1,300 ft).
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 as traditionally defined.[18][19] Instead, they suggest threeclades within the family; one consisting of the northern sea lions (Eumetopias andZalophus), one of the northern fur seal (Callorhinus) and its extinct relatives, and the third of all the remaining Southern Hemisphere species.[20]
^Lento, G.M.; Hickson, R.E.; Chambers, G.K.; Penny, D. (1 January 1995). "Use of spectral analysis to test hypotheses on the origin of pinnipeds".Molecular Biology and Evolution.12 (1):28–52.doi:10.1093/oxfordjournals.molbev.a040189.PMID7877495.
^Wynen, L; Goldsworthy, SD; Insley, SJ; Adams, M; Bickham, JW; Francis, J; Gallo, JP; Hoelzel, AR; et al. (2001). "Phylogenetic relationships within the eared seals (Otariidae: Carnivora): implications for the historical biogeography of the family".Mol. Phylogenet. Evol.21 (2):270–284.Bibcode:2001MolPE..21..270W.doi:10.1006/mpev.2001.1012.PMID11697921.
^(in Japanese)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 ofRebun Island, northern Hokkaido."
^Yonezawa, T.; et al. (2009). "The monophyletic origin of sea lions and fur seals (Carnivora; Otariidae) in the Southern Hemisphere".Gene.441 (1–2):89–99.doi:10.1016/j.gene.2009.01.022.PMID19254754.
^Berta, A.; Churchill, M. (2012). "Pinniped Taxonomy: evidence for species and subspecies".Mammal Review.42 (3):207–234.doi:10.1111/j.1365-2907.2011.00193.x.
