Editing Bear (section)

==Physical characteristics==
===Size===
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The bear family includes the most massive extant terrestrial members of the order Carnivora.{{efn|Treating [[pinniped]]s<ref name="Illiger1811">{{Cite book|last=Illiger|first=J. K. W.|title=Prodromus Systematis Mammalium et Avium|year=1811|publisher=Sumptibus C.&nbsp;Salfeld|pages=138–39|url=https://archive.org/stream/caroliilligerida00illi#page/138/mode/2up|language=la}}</ref> as [[marine mammal]]s.}} The polar bear is considered to be the largest extant species,<ref>{{Harvnb|Ward|Kynaston|1995|p=61}}</ref> with adult males weighing {{cvt|350|-|700|kg}} and measuring {{cvt|2.4|-|3|m}} in total length.<ref>{{cite book|ref=Hemstock|title=The Polar Bear|last=Hemstock|first=Annie|year=1999|publisher=Capstone Press|location=Manakato, MN|isbn=978-0-7368-0031-0|page=[https://archive.org/details/polarbear0000hems/page/4 4]|url=https://archive.org/details/polarbear0000hems/page/4 }}</ref> The smallest species is the sun bear, which ranges {{cvt|25|–|65|kg}} in weight and {{cvt|100|–|140|cm}} in length.<ref>{{cite journal|last1=Fitzgerald|first1=C. S.|last2=Krausman|first2=P. S.|year=2002|title=Helarctos malayanus|journal=Mammalian Species|issue=696|pages=1–5|doi=10.1644/1545-1410(2002)696<0001:HM>2.0.CO;2|s2cid=198969265 }}</ref> Prehistoric [[Arctodus|North]] and [[South American short-faced bear]]s were the largest species known to have lived. The latter estimated to have weighed {{cvt|1,600|kg}} and stood {{cvt|3.4|m}} tall.<ref name="Dell'Amore2011">{{citation|last=Dell'Amore|first=C.|date=February 3, 2011|url=http://news.nationalgeographic.com/news/2011/02/110203-biggest-bear-largest-giant-short-faced-animals-science/|title=Biggest Bear Ever Found|archive-url=https://web.archive.org/web/20171017130448/http://news.nationalgeographic.com/news/2011/02/110203-biggest-bear-largest-giant-short-faced-animals-science/|archive-date=2017-10-17|publisher=[[National Geographic Society|National Geographic]] News}}</ref><ref name="Soibelzon2">{{Cite journal|last1=Soibelzon|first1=L. H.|last2=Schubert|first2=B. W.|title=The Largest Known Bear, ''Arctotherium angustidens'', from the Early Pleistocene Pampean Region of Argentina: With a Discussion of Size and Diet Trends in Bears|journal=[[Journal of Paleontology]]|volume=85|issue=1|pages=69–75|date=January 2011|url=http://jpaleontol.geoscienceworld.org/cgi/content/abstract/85/1/69|doi=10.1666/10-037.1|s2cid=129585554|access-date=2011-06-01|archive-url=https://web.archive.org/web/20110310053427/http://jpaleontol.geoscienceworld.org/cgi/content/abstract/85/1/69|archive-date=2011-03-10|url-status=live|hdl=11336/104215|hdl-access=free}}</ref> Body weight varies throughout the year in bears of temperate and arctic climates, as they build up fat reserves in the summer and autumn and lose weight during the winter.<ref name="Marshall Cavendish"/>

===Morphology===
[[File:Bear foot.jpg|thumb|left|upright=1.2|Unlike most other [[carnivora]]ns, bears have [[plantigrade]] feet. Drawing by [[Richard Owen]], 1866.]]

Bears are generally bulky and robust animals with short tails. They are [[sexual dimorphism|sexually dimorphic]] with regard to size, with males typically being larger.<ref name=Derocheretal86>{{cite journal |last=Derocher |first=Andrew E. |author2=Andersen, Magnus |author3=Wiig, Øystein |title=Sexual dimorphism of polar bears |journal=Journal of Mammalogy |year=2005 |volume=86 |issue=5 |pages=895–901 |doi=10.1644/1545-1542(2005)86[895:SDOPB]2.0.CO;2 |doi-access=free }}</ref><ref name=Hunt98>{{Cite book |author=Hunt, R. M. Jr. |year=1998 |chapter=Ursidae |editor1=Janis, Christine M. |editor2=Scott, Kathleen M. |editor3=Jacobs, Louis L. |title=Evolution of Tertiary Mammals of North America, volume 1: Terrestrial carnivores, ungulates, and ungulatelike mammals |location=Cambridge, England |publisher=Cambridge University Press |pages=174–195 |isbn=978-0-521-35519-3}}</ref> Larger species tend to show increased levels of sexual dimorphism in comparison to smaller species.<ref name=Hunt98/> Relying as they do on strength rather than speed, bears have relatively short limbs with thick bones to support their bulk. The [[Scapula|shoulder blades]] and the [[pelvis]] are correspondingly massive. The limbs are much straighter than those of the [[big cat]]s as there is no need for them to flex in the same way due to the differences in their gait. The strong forelimbs are used to catch prey, excavate dens, dig out burrowing animals, turn over rocks and logs to locate prey, and club large creatures.<ref name="Marshall Cavendish"/>

[[File:Black bear large.jpg|thumb|upright|Despite being [[quadruped]]s, bears can stand and sit as humans do, as demonstrated by this [[American black bear]].]]
Unlike most other land carnivorans, bears are [[plantigrade]]. They distribute their weight toward the hind feet, which makes them look lumbering when they walk. They are capable of bursts of speed but soon tire, and as a result mostly rely on ambush rather than the chase. Bears can stand on their hind feet and sit up straight with remarkable balance. Their front paws are flexible enough to grasp fruit and leaves. Bears' non-retractable claws are used for digging, climbing, tearing, and catching prey. The claws on the front feet are larger than those on the back and may be a hindrance when climbing trees; black bears are the most arboreal of the bears, and have the shortest claws. Pandas are unique in having a bony extension on the wrist of the front feet which acts as a thumb, and is used for gripping [[bamboo]] shoots as the animals feed.<ref name="Marshall Cavendish"/>

Most mammals have [[Agouti (coloration)|agouti]] hair, with each individual hair shaft having bands of color corresponding to two different types of [[melanin]] pigment. Bears however have a single type of melanin and the hairs have a single color throughout their length, apart from the tip which is sometimes a different shade. The coat consists of long guard hairs, which form a protective shaggy covering, and short dense hairs which form an insulating layer trapping air close to the skin. The shaggy coat helps maintain body heat during winter hibernation and is shed in the spring leaving a shorter summer coat. Polar bears have hollow, translucent guard hairs which gain heat from the sun and conduct it to the dark-colored skin below. They have a thick layer of blubber for extra insulation, and the soles of their feet have a dense pad of fur.<ref name="Marshall Cavendish"/> While bears tend to be uniform in color, some species may have markings on the chest or face and the giant panda has a bold black-and-white pelage.<ref name="Ward124"/>

Bears have small rounded ears so as to minimize heat loss, but neither their hearing or sight are particularly acute. Unlike many other carnivorans they have [[color vision]], perhaps to help them distinguish ripe nuts and fruits. They are unique among carnivorans in not having touch-sensitive [[whiskers]] on the muzzle; however, they have an excellent [[olfaction|sense of smell]], better than that of the dog, or possibly any other mammal. They use smell for signalling to each other (either to warn off rivals or detect mates) and for finding food. Smell is the principal sense used by bears to locate most of their food, and they have excellent memories which helps them to relocate places where they have found food before.<ref name="Marshall Cavendish"/>

[[File:Ursus arctos 01 MWNH 145 (cropped).JPG|thumb|left|Brown bear skull]]

The [[skull]]s of bears are massive, providing anchorage for the powerful [[Masseter muscle|masseter]] and [[temporal muscle|temporal]] jaw muscles. The [[canine tooth|canine teeth]] are large but mostly used for display, and the [[molar (tooth)|molar]] teeth flat and crushing. Unlike most other members of the Carnivora, bears have relatively undeveloped [[carnassial]] teeth, and their teeth are adapted for a diet that includes a significant amount of vegetable matter.<ref name="Marshall Cavendish">{{cite book |author=Anon |title=Mammal Anatomy: An Illustrated Guide |url=https://books.google.com/books?id=mTPI_d9fyLAC&pg=PA104 |year=2010 |publisher=Marshall Cavendish |isbn=978-0-7614-7882-9 |pages=104–123}}</ref> Considerable variation occurs in [[dentition|dental formula]] even within a given species. This may indicate bears are still in the process of evolving from a mainly meat-eating diet to a predominantly herbivorous one. Polar bears appear to have secondarily re-evolved carnassial-like cheek teeth, as their diets have switched back towards carnivory.<ref name=EoM>{{cite book |editor=Macdonald, D. |author=Bunnell, Fred |year=1984 |title=The Encyclopedia of Mammals |publisher=Facts on File |page=[https://archive.org/details/encyclopediaofma00mals_0/page/87 87] |isbn=978-0-87196-871-5 |url=https://archive.org/details/encyclopediaofma00mals_0/page/87 }}</ref> Sloth bears lack lower central incisors and use their protrusible lips for sucking up the termites on which they feed.<ref name="Marshall Cavendish"/> The general dental formula for living bears is: {{DentalFormula|upper=3.1.2–4.2|lower=3.1.2–4.3}}.<ref name="Marshall Cavendish"/> The structure of the [[larynx]] of bears appears to be the most [[Basal (phylogenetics)|basal]] of the caniforms.<ref name="Ward117"/> They possess air pouches connected to the [[pharynx]] which may [[vocal resonance|amplify]] their vocalizations.<ref>{{cite journal |author1=Weissengruber, G. E. |author2=Forstenpointner, G. |author3=Kübber-Heiss, A. |author4=Riedelberger, K. |author5=Schwammer, H. |author6=Ganzberger, K. |year=2001 |title=Occurrence and structure of epipharyngeal pouches in bears (Ursidae) |journal=Journal of Anatomy |volume=198 |issue=3 |pages=309–14 |pmid=11322723 |pmc=1468220   |doi=10.1046/j.1469-7580.2001.19830309.x }}</ref>

Bears have a fairly simple digestive system typical for carnivorans, with a single stomach, short undifferentiated intestines and no [[cecum]].<ref>{{cite book |author1=Schwartz, C. C. |author2=Miller, S. D. |author3=Haroldson, M. A. |contribution=Grizzly Bear |title=Wild Mammals of North America; biology, management, and conservation |publisher=Johns Hopkins University Press |editor1=Feldhamer, G.|editor2=Thompson, B.|editor3=Chapman, J. |page=562 |isbn=978-0-8018-7416-1|url=https://books.google.com/books?id=-xQalfqP7BcC|date=2003-11-19 }}</ref><ref name="nps"/> Even the herbivorous giant panda still has the digestive system of a carnivore, as well as carnivore-specific genes. Its ability to digest [[cellulose]] is ascribed to the microbes in its gut.<ref>{{cite journal | author=Ruiqiang Li | title=The sequence and de novo assembly of the giant panda genome | journal=Nature | volume=463 | issue=21 | pages=311–317 | year=2010 | pmid=20010809 | pmc=3951497 | doi=10.1038/nature08696 | bibcode=2010Natur.463..311L |last2=Fan | first2=Wei | last3=Tian | first3=Geng | last4=Zhu | first4=Hongmei | last5=He | first5=Lin | last6=Cai | first6=Jing | last7=Huang | first7=Quanfei | last8=Cai | first8=Qingle | last9=Li | first9=Bo | last10=Bai | first10=Yinqi | last11=Zhang | first11=Zhihe | last12=Zhang | first12=Yaping | last13=Wang | first13=Wen | last14=Li | first14=Jun | last15=Wei | first15=Fuwen | last16=Li | first16=Heng | last17=Jian | first17=Min | last18=Li | first18=Jianwen | last19=Zhang | first19=Zhaolei | last20=Nielsen | first20=Rasmus | last21=Li | first21=Dawei | last22=Gu | first22=Wanjun | last23=Yang | first23=Zhentao | last24=Xuan | first24=Zhaoling | last25=Ryder | first25=Oliver A. | last26=Leung | first26=Frederick Chi-Ching | last27=Zhou | first27=Yan | last28=Cao | first28=Jianjun | last29=Sun | first29=Xiao | last30=Fu | first30=Yonggui | display-authors=29 }}</ref> Bears must spend much of their time feeding in order to gain enough nutrition from foliage. The panda, in particular, spends 12–15 hours a day feeding.<ref name="Ward83"/>