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Eared seal

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Title: Eared seal  
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Subject: Marine mammal, Carnivora, California sea lion, Sea lion, Pinniped
Collection: Burdigalian First Appearances, Eared Seals, Pinnipeds
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Eared seal

Eared seals
Temporal range: 12–0Ma
Є
O
S
D
C
P
T
J
K
Pg
N
Late Miocene to Recent
An Australian sea lion
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Suborder: Caniformia
Superfamily: Pinnipedia
Family: Otariidae
Gray, 1825
Genera

Arctocephalus
Callorhinus
Eumetopias
Neophoca
Otaria
Phocarctos
Zalophus

Ear flaps of Otaria flavescens

An eared seal or otariid or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera (another species became extinct in the 1950s) and are commonly known either as sea lions or fur seals, 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 and Southern Oceans and the southern Indian and Atlantic Oceans. They are conspicuously absent in the north Atlantic.

The words 'otariid' and 'otary' come from the Greek otarion meaning "little ear",[1] referring to the small but visible external ear flaps (pinnae), which distinguishes them from the phocids.

Contents

  • Evolution and taxonomy 1
  • Anatomy and appearance 2
  • Behavior 3
  • Species 4
  • References 5
  • Further reading 6
  • External links 7

Evolution and taxonomy



Phocidae (true seals)


Otariidae





Antarctic fur seal



Guadalupe fur seal


Juan Fernández fur seal





Galápagos fur seal


southern fur seal





Australian sea lion


New Zealand sea lion




subantarctic fur seal


brown fur seal


South American sea lion







California sea lion


Galápagos sea lion



Japanese sea lion



Steller sea lion




northern fur seal


Odobenidae  walrus



Cladogram showing the eared seals, Otariidae, and their relationships with other pinnipeds, combining several phylogenetic analyses.[2]

Along with the Phocidae and Odobenidae, the two other members of Pinnipedia, Otаriidae are descended from a common ancestor most closely related to modern bears.[3] Debate remains as to whether the phocids diverged from the otariids before or after the walrus.

Otariids arose in the late Miocene (10-12 million years ago) in the North Pacific, diversifying rapidly into the Southern Hemisphere, where most species now live. The genus Callorhinus (northern fur seal) has the oldest fossil record of any extant otariid, extending to the middle Pliocene, and probably arose from the extinct fur seal 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.[4] Recent analyses of the

  • Eared Seals on Answers.com
  • Otariids on MarineBio.org

External links

  • 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.

Further reading

  1. ^ "Otary, n., etymology of" The Oxford English Dictionary. 2nd ed. 1989. OED Online. Oxford University Press. http://dictionary.oed.com/ Accessed November 2007
  2. ^ Berta, A.; Churchill, M. (2012). "Pinniped taxonomy: Review of currently recognized species and subspecies, and evidence used for their description". Mammal Review 42 (3): 207–34.  
  3. ^ 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.  
  4. ^ J.E. King (1983). Seals of the World (2nd ed.). New York: Cornell University Press.  
  5. ^ 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. Phylog. Evol. 21 (2): 270–284.  
  6. ^ Brunner, S. (2003). "Fur seals and sea lions (Otariidae): identification of species and taxonomic review". Systematics and Biodiversity 1 (3): 339–439.  
  7. ^ "Otariidae".  
  8. ^ Weckerly, FW (1998). "Sexual-size dimorphism: influence of mass and mating systems in the most dimorphic mammals.". Journal of Mammalogy 79 (1): 33–42.  
  9. ^ 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.  
  10. ^ Arnason, U., et al. (2006). "Pinniped phylogeny and a new hypothesis for their origin and dispersal". Molecular Phylogenetics and Evolution 41 (2): 345–354.  
  11. ^ Berta, A. & Churchill, M. (2012). "Pinniped Taxonomy: evidence for species and subspecies". Mammal Review 42 (3): 207–234.  

References

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.[9][10] Instead, they suggest three clades 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.[11]

Family Otariidae

Species

Otariids are carnivorous, feeding on fish, squid and krill. Sea lions tend to feed closer to shore in upwelling 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).

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

Behavior

Male otariids range in size from the 70-kg (150-lb) Galápagos fur seal, smallest of all pinnipeds, 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 of all mammals.[8]

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: 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 commercial exploitation.

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.

Eared seal off the Namibian coast.

Anatomy and appearance

, 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. sexual dimorphism 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 [7][6]

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