Eared seal

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",[2] referring to the small but visible external ear flaps (pinnae), which distinguishes them from the phocids.

Eared seals
Temporal range: Miocene-Holocene,[1] 17.1–0 Ma
Neophoca cinerea
An Australian sea lion (Neophoca cinerea)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Superfamily: Otarioidea
Family: Otariidae
Gray, 1825
Type species
Otaria flavescens
(Shaw, 1800)
Genera

Arctocephalus
Callorhinus
Eotaria
Eumetopias
Neophoca
Otaria
Phocarctos
Pithanotaria
Proterozetes
Thalassoleon
Zalophus

Otaria fg02
Ear flaps of Otaria flavescens

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.[3]

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.[4] Debate remains as to whether the phocids diverged from the otariids before or after the walrus.

Otariids arose in the Miocene (15-17 million years ago) in the North Pacific, diversifying rapidly into the Southern Hemisphere, where most species now live. The earliest known fossil osariid is Eotaria crypta from southern California,[1] 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.[5] Recent analyses of the genetic evidence suggests that Callorhinus ursinus is in fact more closely related to several sea lion species.[6] 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 family Otariidae has been organized into seven genera with 16 species and two subspecies.[7][8] 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, 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

Ohrenrobbe vor der Küste Namibias
Eared seal off the Namibian coast.

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: 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.

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.[9]

Behavior

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.

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).

Species

Family Otariidae

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.[12][13] 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.[14]

References

  1. ^ a b Boessenecker, R. W.; Churchill, M. (2015). "The oldest known fur seal". Biology Letters. 11 (2): 20140835. doi:10.1098/rsbl.2014.0835. PMC 4360102. PMID 25672999.
  2. ^ "Otary, n., etymology of" The Oxford English Dictionary. 2nd ed. 1989. OED Online. Oxford University Press. http://dictionary.oed.com/ Accessed November 2007
  3. ^ 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. doi:10.1111/j.1365-2907.2011.00193.x.
  4. ^ 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. PMID 7877495.
  5. ^ J.E. King (1983). Seals of the World (2nd ed.). New York: Cornell University Press. ISBN 978-0-7022-1694-7.
  6. ^ 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. doi:10.1006/mpev.2001.1012. PMID 11697921.
  7. ^ 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.
  8. ^ "Otariidae". Integrated Taxonomic Information System. Retrieved November 2007. Check date values in: |accessdate= (help)
  9. ^ 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.
  10. ^ Aurioles, D. & Trillmich, F. (IUCN SSC Pinniped Specialist Group) (2008). "Zalophus japonicus". IUCN Red List of Threatened Species. Version 2008. International Union for Conservation of Nature. Retrieved 7 January 2009.
  11. ^ (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 of Rebun Island, northern Hokkaido."
  12. ^ 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. PMID 19254754.
  13. ^ Arnason, U.; et al. (2006). "Pinniped phylogeny and a new hypothesis for their origin and dispersal". Molecular Phylogenetics and Evolution. 41 (2): 345–354. doi:10.1016/j.ympev.2006.05.022. PMID 16815048.
  14. ^ 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.

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.

External links

2017 in mammal paleontology

This article records new taxa of fossil mammals of every kind that have been described during the year 2017, as well as other significant discoveries and events related to paleontology of mammals that occurred in the year 2017.

Bouvet Island

Bouvet Island (Norwegian: Bouvetøya) is an uninhabited subantarctic high island and dependency of Norway located in the South Atlantic Ocean at 54°25′S 3°22′E, thus locating it north of and outside the Antarctic Treaty System. It lies at the southern end of the Mid-Atlantic Ridge and is the most remote island in the world, approximately 1,700 kilometres (1,100 mi) north of the Princess Astrid Coast of Queen Maud Land, Antarctica and 2,600 kilometres (1,600 mi) south-southwest of the coast of South Africa.

The island has an area of 49 square kilometres (19 sq mi), of which 93 percent is covered by a glacier. The centre of the island is an ice-filled crater of an inactive volcano. Some skerries and one smaller island, Larsøya, lie along the coast. Nyrøysa, created by a rock slide in the late 1950s, is the only easy place to land and is the location of a weather station.

The island was first spotted on 1 January 1739 by Frenchman Jean-Baptiste Charles Bouvet de Lozier, on a French exploration mission in the South Atlantic with the ships Aigle and Marie. They did not make a landfall, and he mislabeled the coordinates for the island and the island was not sighted again until 1808, when the British whaler captain James Lindsay named it Lindsay Island. The first claim of landing, although disputed, was by American sailor Benjamin Morrell. In 1825, the island was claimed for the British Crown by George Norris, who named it Liverpool Island. He also reported Thompson Island as nearby, although this was later shown to be a phantom island. The first Norvegia expedition landed on the island in 1927 and claimed it for Norway. At this time the island was named Bouvet Island, or "Bouvetøya" in Norwegian. After a dispute with the United Kingdom, it was declared a Norwegian dependency in 1930. It became a nature reserve in 1971.

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 lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic; males are larger than females, and have a thicker neck, and protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by orcas and white sharks.

California sea lions have a polygynous breeding pattern. From May to August, males establish territories and try to attract females with which to mate. Females are free to move in between territories, and are not coerced by males. Mothers nurse their pups in between foraging trips. Sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside their breeding season, sea lions spend much of their time at sea, but they come to shore to molt.

Sea lions are particularly intelligent, can be trained to perform various tasks and display limited fear of humans if accustomed to them. Because of this, California sea lions are a popular choice for public display in zoos, circuses and oceanariums, and are trained by the United States Navy for certain military operations. The International Union for Conservation of Nature (IUCN) lists the species as Least Concern due to its abundance. To protect fish, the US states of Oregon and Washington engage in annual kill quotas of sea lions.

Earless seal

The earless seals, phocids or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae . They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

Northern fur seal

The northern fur seal (Callorhinus ursinus) 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 (Arctocephalinae) and the only living species in the genus Callorhinus. A single fossil species, Callorhinus gilmorei, is known from the Pliocene of Japan and western North America.

Wildlife of China

China's vast and diverse landscape is home to a profound variety and abundance of wildlife. As of one of 17 megadiverse countries in the world, China has, according to one measure, some 7,516 species of vertebrates including 4,936 fish, 1,269 bird, 562 mammal, 403 reptile and 346 amphibian species. In terms of the number of species, China ranks third in the world in mammals, eighth in birds, seventh in reptiles and seventh in amphibians. In each category, China is the most biodiverse country outside of the tropics.Many species of animals are endemic to China, including the country's most famous wildlife species, the giant panda. In all, about one-sixth of mammal species and two-thirds of amphibian species in China are endemic to the country.Wildlife in China share habitat with and bear acute pressure from the world's largest population of humans. At least 840 animal species are threatened, vulnerable or in danger of local extinction in China, due mainly to human activity such as habitat destruction, pollution and poaching for food, fur and ingredients for traditional Chinese medicine. Endangered wildlife is protected by law, and as of 2005, the country has over 2,349 nature reserves, covering a total area of 149.95 million hectares (578,960 square miles), about 15 percent of China's total land area.

Extant Carnivora species

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