Editing Polar bear (section)

==Characteristics==
{{Multiple image
| align             = left
| direction         = vertical
| width             = 
| image1            = Description iconographique comparée du squelette et du système dentaire des mammifères récents et fossiles (Ursus maritimus skeleton).jpg
| caption1          = Polar bear skeleton
| image2            = Ursus maritimus 02 MWNH 420.JPG
| caption2          = Bear skull
}}
The polar bear is the largest living species of bear and land [[carnivore]], though some brown bear subspecies like the [[Kodiak bear]] can rival it in size.{{sfn|Derocher|2012|p=10}}{{sfn|Ellis|2009|p=74}} Males are generally {{cvt|200|–|250|cm|ft}} long with a weight of {{cvt|300|–|800|kg}}. Females are smaller at {{cvt|180|–|200|cm|ft}} with a weight of {{cvt|150|–|300|kg}}.<ref name="DeMaster1981">{{cite journal |last1=DeMaster |first1=Douglas P. |last2=Stirling |first2=Ian |date=8 May 1981 |title= ''Ursus maritimus''|jstor=3503828 |journal=Mammalian Species |pages=1–7 |doi=10.2307/3503828 |oclc=46381503 |issue=145 |doi-access=free }}</ref> [[Sexual dimorphism]] in the species is particularly high compared with most other mammals.{{sfn|Ellis|2009|p=75}} Male polar bears also have proportionally larger heads than females.{{sfn|Ellis|2009|p=80}} The weight of polar bears fluctuates during the year, as they can bulk up on fat and increase their mass by 50 percent.{{sfn|Derocher|2012|p=10}} A fattened, pregnant female can weigh as much as {{cvt|500|kg}}.{{sfn|Stirling|2011|p=38}} Adults may stand {{cvt|130|–|160|cm|ft}} tall at the shoulder. The tail is {{cvt|76|–|126|mm}} long.<ref name="DeMaster1981"/> The largest polar bear on record, reportedly weighing {{cvt|1002|kg}}, was a male shot at [[Kotzebue Sound]] in northwestern Alaska in 1960.<ref name="Wood">{{cite book |last=Wood |first=G. L. |year=1983 |title=The Guinness Book of Animal Records |page=[https://archive.org/details/guinnessbookofan00wood/page/27/mode/2up?q=polar+bear 28] |isbn=978-0-85112-235-9 |url=https://archive.org/details/guinnessbookofan00wood/page/27/mode/2up?q=polar+bear |publisher=Guinness Superlatives }}</ref>

Compared with the brown bear, this species has a more slender build, with a narrower, flatter and smaller skull, a longer neck, and a lower shoulder hump.{{sfn|Derocher|2012|p=10}}<ref name=Slater2010/> The snout profile is curved, resembling a "[[Roman nose]]".{{sfn|Derocher|2012|p=10}} They have 34–42 teeth including 12 [[incisor]]s, 4 [[Canine tooth|canines]], 8–16 [[premolar]]s and 10 [[Molar (tooth)|molar]]s. The teeth are adapted for a more carnivorous diet than that of the brown bear, having longer, sharper and more spaced out canines, and smaller, more pointed [[cheek teeth]] (premolars and molars).{{sfn|Ellis|2009|p=75}}{{sfn|Derocher|2012|p=17}}<ref name=Slater2010>{{cite journal|last1=Slater|first1=G. J.|last2=Figueirido|first2=B.|last3=Louis|first3=L.|last4=Yang|first4=P.|last5=Van Valkenburgh|first5=B.|year=2010|title=Biomechanical consequences of rapid evolution in the polar bear lineage|journal=PLOS ONE|volume=5|issue=11|page=e13870|doi=10.1371/journal.pone.0013870 |pmid=21079768 |pmc=2974639 |bibcode=2010PLoSO...513870S |doi-access=free }}</ref> The species has a large space or [[diastema]] between the canines and cheek teeth, which may allow it to better bite into prey.{{sfn|Derocher|2012|p=17}}<ref name=Figueirido>{{cite journal|last1=Figueirido|first1=B.|last2=Palmqvist|first2=P.|last3=Pérez-Claros|first3=J. A.|year=2009|title=Ecomorphological correlates of craniodental variation in bears and paleobiological implications for extinct taxa: an approach based on geometric morphometrics|journal=Journal of Zoology|volume=277|issue=1|pages=70–80|doi=10.1111/j.1469-7998.2008.00511.x}}</ref> Since it normally preys on animals much smaller than it, the polar bear does not have a particularly strong bite.<ref name=Figueirido/> Polar bears have large paws, with the front paws being broader than the back. The feet are hairier than in other bear species, providing warmth and friction when stepping on snow and sea ice.{{sfn|Derocher|2012|p=22}} The claws are small but sharp and hooked and are used both to snatch prey and climb onto ice.{{sfn|Derocher|2012|p=21}}{{sfn|Ellis|2009|p=79}}
[[File:Polar Bear AdF.jpg|thumb|right|Polar bear jumping on floating ice at [[Svalbard]]]]
The coat consists of dense [[underfur]] around {{convert|5|cm|abbr=on}} long and [[guard hair]]s around {{convert|15|cm|abbr=on}} long.<ref name="DeMaster1981"/> Males have long hairs on their forelegs, which is thought to signal their [[Fitness (biology)|fitness]] to females.<ref name="Dimorph">{{cite journal|last1=Derocher|first1=Andrew E.|first2=Magnus |last2=Andersen|first3=Øystein |last3=Wiig|year=2005|title=Sexual dimorphism of polar bears|jstor=4094434|journal=Journal of Mammalogy|volume=86|issue=5|pages=895–901|doi=10.1644/1545-1542(2005)86[895:SDOPB]2.0.CO;2|doi-access=free }}</ref> The outer surface of the hairs has a scaly appearance, and the guard hairs are hollow, which allows the animals to trap heat and float in the water.{{sfn|Derocher|2012|pp=7–8}} The transparent guard hairs [[forward scatter]] [[ultraviolet]] light between the underfur and the skin, leading to a cycle of absorption and re-emission, keeping them warm.<ref name=Khattab/> The fur appears white because of the [[backscatter]] of [[Ray (optics)#Interaction with surfaces|incident light]] and the absence of pigment.<ref name=Khattab>{{cite journal|last1=Khattab|first1=M. Q.|last2=Tributsch|first2=H.|year=2015|title=Fibre-optical light scattering technology in polar bear hair: A re-evaluation and new results|journal=Journal of Advanced Biotechnology and Bioengineering|volume=3|issue=2|pages=38–51|doi=10.12970/2311-1755.2015.03.02.2}}</ref>{{sfn|Derocher|2012|p=7}} Polar bears gain a yellowish colouration as they are exposed more to the sun. This is reversed after they [[moulting|moult]]. It can also be grayish or brownish.<ref name="DeMaster1981"/> Their light fur provides [[camouflage]] in their snowy environment. After emerging from the water, the bear can easily shake itself dry since the hairs are resistant to tangling when wet.{{sfn|Ellis|2009|pp=65, 72}} Oil secretions prevent the hair from freezing.<ref>{{cite journal|last1=Carolan|first1=J|last2=Jakubec|first2=M|last3=Xaiver|first3=N. F.|last4=Motala|first4=A. P.|last5=Bifulco|first5=E|last6=Aars|first6=J|last7=Anderson|first7=M|last8=Schmidt|first8=A. L.|last9=Cabré|first9=M. B.|last10=Singh|first10=V|last11=Colavita|first11=P. E.|last12=Selfors|first12=E. W.|last13=Sacchi|first13=M|last14=O'Reilly|first14=S|last15=Halskau|first15=Ø|last16=Tiwari|first16=M. K.|last17=Hobbs|first17=R. G.|last18=Holst|first18=B|year=2025|title=Anti-icing properties of polar bear fur|journal=Science Advances|volume=11|issue=5|pages=eads7321|doi=10.1126/sciadv.ads7321|pmid=39879302|pmc=11777201|bibcode=2025SciA...11S7321C}}</ref> The skin, including the nose and lips, is black and absorbs heat.<ref name="DeMaster1981"/><ref name=Khattab/> Polar bears have a {{cvt|5|–|10|cm}} thick layer of fat underneath the skin,<ref name="DeMaster1981"/> which provides both warmth and energy.{{sfn|Derocher|2012|p=12}} Polar bears maintain their core body temperature at about {{cvt|36.9|C}}.<ref>{{cite journal|last=Best|first=R. C.|year=1982|title=Thermoregulation in resting and active polar bears|journal=Journal of Comparative Physiology A|volume=146|pages=63–73|doi=10.1007/BF00688718|s2cid=36351845 }}</ref> Overheating is countered by a layer of highly vascularized [[striated muscle tissue]] and finely controlled blood vessels. Bears also cool off by entering the water.<ref name=Khattab/><ref>{{cite journal|last1=Tributsch|first1=H.|last2=Goslowsky|first2=H.|last3=Küppers|first3=U.|last4=Wetzel|first4=H.|year=1990|title=Light collection and solar sensing through the polar bear pelt|journal=Solar Energy Materials|volume=21|issue=2–3|pages=219–236|doi=10.1016/0165-1633(90)90056-7}}</ref>

The eyes of a polar bear are close to the top of the head, which may allow them to stay out of the water when the animal is swimming at the surface. They are relatively small, which may be an adaption against blowing snow and [[Photokeratitis|snow blindness]]. Polar bears are [[Dichromacy|dichromats]], and lack the [[cone cell]]s for seeing medium, mainly green, wavelengths. They have many [[rod cell]]s, which allow them to see at night. The ears are small, allowing them to retain heat and not get [[frost bite|frostbitten]].{{sfn|Derocher|2012|pp=14, 16, 18–19}} They can hear best at frequencies of 11.2–22.5&nbsp;kHz, a wider frequency range than expected given that their prey mostly makes low-frequency sounds.<ref>{{cite journal|last1=Nachtigall|first1=P. E.|last2=Supin|first2=A. Y.|last3=Amundin|first3=M.|last4=Röken|first4=B.|last5=Møller|first5=T.|last6=Mooney|first6=T. A.|last7=Taylor|first7=K. A.|last8=Yuen|first8=M.|year=2007|title=Polar bear ''Ursus maritimus'' hearing measured with auditory evoked potentials|journal=Journal of Experimental Biology|volume=210|issue=7|pages=1116–1122|doi=10.1242/jeb.02734|pmid=17371910 |s2cid=18046149 |doi-access=free|bibcode=2007JExpB.210.1116N }}</ref> The [[nasal concha]] creates a large surface area, so more warm air can move through the nasal passages.{{sfn|Derocher|2012|p=14}} Their [[olfactory system]] is also large and adapted for smelling prey over vast distances.<ref>{{cite journal|last1=Green|first1=P. A.|last2=Van Valkenburgh|first2=B.|last3=Pang|first3=B.|last4=Bird|first4=B.|last5=Rowe|first5=T.|last6=Curtis|first6=A.|year=2012|title=Respiratory and olfactory turbinal size in canid and arctoid carnivorans|journal=Journal of Anatomy|volume=221|issue=6|pages=609–621|doi=10.1111/j.1469-7580.2012.01570.x|pmid=23035637 |pmc=3512284 }}</ref> The animal has [[reniculate kidney]]s which filter out the salt in their food.{{sfn|Derocher|2012|p=26}}