font settings

Font Size: Large | Normal | Small
Font Face: Verdana | Geneva | Georgia

Otariidae

(Family)

Overview

[ Back to top ]

The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the Walrus (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 and Atlantic oceans. They are conspicuously absent in the north Atlantic.

The name otariid comes from the Greek otarion meaning "little ear",1] referring to the small but visible external ear flaps (pinnae) which can be used to distinguish them from the phocids.

Evolution and taxonomy

[ Back to top ]

Along with the Phocidae and O dobenidae, the two other members of Pinnipedia, Ot?riidae are descended from a common ancestor most closely related to modern bears.[2] There remains debate 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. 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.[3] Recent analyses of the genetic evidence suggests that the Callorhinus ursinus is in fact more closely related to several sea lion species.[4] Furthermore, many of the Otariinae appear to be more phylogenetically 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 (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.[5][6] 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. 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

[ Back to top ]
California Sea Lions

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 for eared seals is: Upper: 3.1.4.1-3, lower: 2.1.4.1. 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.

Male otariids range in size from the 70 kg (150 lbs) Galapagos Fur Seal, 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.[7]

Behavior

[ Back to top ]

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, 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 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.

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 and some females are capable of dives up to 400 m (1300 ft).

Species

[ Back to top ]
" 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. 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

[ Back to top ]
California Sea Lions

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 for eared seals is: Upper: 3.1.4.1-3, lower: 2.1.4.1. 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.

Male otariids range in size from the 70 kg (150 lbs) Galapagos Fur Seal, 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.[7]

Behavior

[ Back to top ]

All otariids breed on land during well-defined breeding seasons. Exc ept 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, 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 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.

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 and some females are capable of dives up to 400 m (1300 ft).

Species

[ Back to top ]

Notes

[ Back to top ]
  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. ^ 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. PMID 7877495. http://mbe.oxfordjournals.org/cgi/reprint/12/1/28. 
  3. ^ J.E. King (1983). Seals of the World (2nd ed.). New York: Cornell University Press. ISBN 978-0702216947. 
  4. ^ 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. doi:10.1006/mpev.2001.1012. PMID 11697921. 
  5. ^ Brunner, S. (2003). "Fur seals and sea lions (Otariidae): identification of species and taxonomic review". Systematics and Biodiversity 1 (3): 339?439. doi:10.1017/S147720000300121X. http://journals.cambridge.org/action/displayAbstract?aid=198243. 
  6. ^ "Otariidae". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=180615. Retrieved November 2007. 
  7. ^ Weckerly, FW (1998). "Sexual-size dimorphism: influence of mass and mating systems in the most dimorphic mammals.". Journal of Mammalogy 79 (1): 33?42. doi:10.2307/1382840. JSTOR 1382840. 

Taxonomy

[ Back to top ]

The Family Otariidae is a member of the Superfamily Phocoidea. Here is the complete "parentage" of Otariidae:

The Family Otariidae is further organized into finer groupings including:

Genera

[ Back to top ]

Arctocephalus

The genus Arctocephalus consists of eight of the nine species of fur seal. For details see the fur seal article, or the individual species articles. [more]

Callorhinus

[more]

Eumetopias

The Steller sea lion (Eumetopias jubatus) also known as the northern sea lion, is a threatened species of sea lion in the northern Pacific. It is the sole member of the genus Eumetopias and the largest of the eared seals (Otariidae). Among pinnipeds, it is inferior in size only to the walrus and the two elephant seals. The species is named for the naturalist Georg Wilhelm Steller, who first described them in 1741. The Steller sea lion has attracted considerable attention in recent decades due to significant, unexplained declines in their numbers over a large portion of their range in Alaska. [more]

Eumetopius

Hydrarctos

Neophoca

The Australian sea lion (Neophoca cinerea) 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. It is monotypic in the genus Neophoca. [more]

Otaria

The South American sea lion (Otaria flavescens, formerly Otaria byronia), 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. Its scientific name was subject to controversy, with some taxonomists referring to it as Otaria flavescens and others referring to it as Otaria byronia. The former eventually won out. Locally, it is known by several names though the most common ones are lobo marino (sea wolf) and le?n marino (sea lion). [more]

Phocarctos

The New Zealand sea lion (Phocarctos hookeri) also known as Hooker's sea lion or whakahao in Maori 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 Islands. It is monotypic of its genus. [more]

Pithanotaria

Pteronarctos

[more]

Thalassoleon

Zalophus

Zalophus is a genus of the family Otariidae (sea lions and fur seals) of order Carnivora. It includes three species of which one became recently extinct: [more]

At least 10 species and subspecies belong to the Genus Zalophus.

More info about the Genus Zalophus may be found here.

Footnotes

[ Back to top ]
  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. ^ 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. PMID 7877495. http://mbe.oxfordjournals.org/cgi/reprint/12/1/28. 
  3. ^ J.E. King (1983). Seals of the World (2nd ed.). New York: Cornell University Press. ISBN 978-0702216947. 
  4. ^ 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. doi:10.1006/mpev.2001.1012. PMID 11697921. 
  5. ^ Brunner, S. (2003). "Fur seals and sea lions (Otariidae): identification of species and taxonomic review". Systematics and Biodiversity 1 (3): 339?439. doi:10.1017/S147720000300121X. http://journals.cambridge.org/action/displayAbstract?aid=198243. 
  6. ^ "Otariidae". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=180615. Retrieved November 2007. 
  7. ^ Weckerly, FW (1998). "Sexual-size dimorphism: influence of mass and mating systems in the most dimorphic mammals.". Journal of Mammalogy 79 (1): 33?42. doi:10.2307/1382840. JSTOR 1382840. 

Further Reading

[ Back to top ]

External links

[ Back to top ]

Sources

[ Back to top ]
Last Revised: August 24, 2012
2012/08/24 13:38:44