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Northern fur seal
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==Description== Northern fur seals have extreme [[sexual dimorphism]], with males being 30β40% longer and more than 4.5 times heavier than adult females.<ref name="iucn status 19 November 2021" /> The head is foreshortened in both sexes because of the very short, down-curved muzzle, and small nose, which extends slightly beyond the mouth in females and moderately in males. The [[pelage]] is thick and luxuriant, with a dense underfur in a creamy color. The underfur is obscured by the longer guard hairs, although it is partially visible when the animals are wet. Features of both fore and hind flippers are unique and diagnostic of the species. Fur is absent on the top of the fore flippers and an abrupt "clean line" is seen across the wrist where the fur ends.<ref name=Audubon>{{RefAudubonMarineMammals}}</ref> The hind flippers are proportionately the longest in any otariid because of extremely long, [[cartilaginous]] extensions on all of the toes.<ref name=Audubon/> Small claws are on digits 2β4, well back from the flap-like end of each digit. The ear [[pinna (anatomy)|pinna]]e are long and conspicuous, and naked of dark fur at the tips in older animals. The mystacial [[vibrissa]]e can be very long, and regularly extend beyond the ears. Adults have all white vibrissae, juveniles and subadults have a mixture of white and black vibrissae, including some that have dark bases and white ends, and pups and yearlings have all black vibrissae. The eyes are proportionately large and conspicuous, especially on females, subadults, and juveniles.<ref>{{Cite web |title=Learn More About Northern Fur Seals |url=https://www.marinemammalcenter.org/animal-care/learn-about-marine-mammals/pinnipeds/northern-fur-seal |access-date=2021-05-07 |website=The Marine Mammal Center }}</ref> [[File:Seal and salmon fisheries and general resources of Alaska (1898) (14786615243).jpg|thumb|1898 depiction of ''callorhinus'' in [[Cumberland Sound]]]] Adult males are stocky in build, and have enlarged (thick and wide) necks. A mane of coarse, longer guard hairs extends from the lower neck to the shoulders.<ref name=Audubon/> and covers the nape, neck, chest, and upper back. While the skulls of adult males are large and robust for their overall size, their heads appear short because of the combination of a short muzzle, and the backs of the head behind the ear pinnae being obscured by the enlarged necks. Adult males have abrupt foreheads formed by the elevation of the crown from development of the [[sagittal]] crests, and thicker fur of the mane on the top of their heads.<ref>{{Cite web |title=Northern Fur Seal (Callorhinus ursinus) Species Profile |url=https://www.adfg.alaska.gov/index.cfm?adfg=northernfurseal.main |access-date=2021-05-07 |website=State of Alaska Β· Department of Fish and Game}}</ref> [[Canine teeth]] are much longer and have a greater diameter in adult males than those found on adult females, and this relationship holds to a lesser extent at all ages. [[Image:Pups 01.jpg|thumb|left|Fur seal pups, including one rare albino]] Adult females, subadults, and juveniles are moderate in build. Distinguishing the sexes is difficult until about age five. The body is modest in size and the neck, chest, and shoulders are sized in proportion with the torso. Adult females and subadults have more complex and variable coloration than adult males. They are dark silver-gray to charcoal above. The flanks, chest, sides, and underside of the neck, often forming a chevron pattern in this area, are cream to tan with rusty tones. Variable cream to rust-colored areas are on the sides and top of the muzzle, chin, and as a "brush stroke" running backwards under the eye. In contrast, adult males are medium gray to black, or reddish to dark brown all over. Their manes can have variable amounts of silver-gray or yellowish tinting on the guard hairs. Pups are blackish at birth, with variable oval areas of buff on the sides, in the axillary area, and on the chin and sides of the muzzle. After three to four months, pups molt to the color of adult females and subadults. Males can be as large as {{cvt|2.1|m}} and {{cvt|270|kg}}. Females can be up to {{cvt|1.5|m}} and weigh {{cvt|50|kg}} or more. Newborns weigh {{cvt|5.4|β|6|kg}}, and are {{cvt|60|β|65|cm}} long. [[Image:Callorhinus ursinus (northern fur seal) skull 5 (33777293428).jpg|thumb|The skull]] The teeth are [[haplodont]], i.e. sharp, conical and mostly single-rooted, as is common with carnivorous marine mammals adapted to tearing fish flesh. As with most caniforms, the upper canines are prominent. The [[dental formula]] of the adult is {{DentalFormula|upper=3.1.4.2|lower=2.1.4.1}}<ref>{{cite journal | last1=Chiasson| first1=B.| date=August 1957 | title= The Dentition of the Alaskan Fur Seal | journal=Journal of Mammalogy | volume=38 | issue=3 | pages=310β319 | doi=10.2307/1376230 | jstor=1376230}}</ref> [[File:Fur seal face.jpg|thumb|Close up of face and ears]] Like other otariids, northern fur seals are built for efficient terrestrial locomotion. Their hind limbs are in a plantigrade stance and are able to rotate under the body for quadrupedal locomotion and support.<ref>{{Cite book |doi = 10.1016/B978-0-12-373553-9.00154-1|chapter = Locomotion, Terrestrial|title = Encyclopedia of Marine Mammals|pages = 672β673|year = 2009|last1 = DemΓ©rΓ©|first1 = Thomas A. |last2 = Yonas|first2 = Joshua H.|isbn = 9780123735539}}</ref> When swimming, there are two different types of movement: locomotion and diving. These seals swim primarily with forelimb propulsion due to their physiology. They have flexible joints between vertebrae for better maneuverability in the water as well as "greater muscular leverage" for pectoral strokes.<ref>{{Cite journal|last=Pierce|first=S.E.|date=June 2011|title=Comparative axial morphology in pinnipeds and its correlation with aquatic locomotory behaviour|journal=Journal of Anatomy|volume=219|issue=4|pages=502β514|doi=10.1111/j.1469-7580.2011.01406.x|pmid=21668895|pmc=3196755}}</ref> Stroke patterns are different for different dive types and locomotion, and stroke rates vary for individuals since there is a relationship between maximum stroke rate and body size.<ref>{{Cite journal|last=Insley|first=S.J.|date=January 2008|title=Acoustic determination of activity and flipper stroke rate in foraging northern fur seal females|url=https://www.int-res.com/articles/esr2008/4/n004p147.pdf|journal= Endangered Species Research|volume=4|pages=147β155|doi=10.3354/esr00050|doi-access=free}}</ref>
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