{{About|the squirrel family (Sciuridae) as a whole}}<!-- High visibility page; likely move vandal target -->

{{Taxobox

| name = Squirrels

| fossil_range = {{fossil range|Late Eocene|Recent|Late [[Eocene]]—Recent}}

| image = Sciuridae.jpg

| image_width = 240px

| image_caption = Various members of the Sciuridae family

| regnum = [[Animal]]ia

| phylum = [[Chordate|Chordata]]

| classis = [[Mammal]]ia

| ordo = [[Rodent]]ia

| subordo = [[Sciuromorpha]]

| familia = '''Sciuridae'''

| familia_authority = [[Johann Fischer von Waldheim|Fischer de Waldheim]], 1817

| subdivision_ranks = [[Subfamilies]] and [[tribe (biology)|tribe]]s

| subdivision =

*Subfamily [[Ratufinae]]

*Subfamily [[Sciurillinae]]

*Subfamily [[Sciurinae]]

**Tribe [[Sciurini]]

**Tribe [[Pteromyini]]

*Subfamily [[Callosciurinae]]

**Tribe [[Callosciurini]]

**Tribe [[Funambulini]]

*Subfamily [[Xerinae]]

**Tribe [[Xerini]]

**Tribe [[Protoxerini]]

**Tribe [[Marmotini]]

and see text

}}

'''Squirrels''' belong to a large [[family (biology)|family]] of small or medium-sized [[rodent]]s called the '''Sciuridae'''. The family includes [[tree squirrel]]s, [[ground squirrel]]s, [[chipmunk]]s, [[marmot]]s (including [[groundhog|woodchuck]]s), [[flying squirrel]]s, and [[prairie dog]]s. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been [[introduced species|introduced]] to Australia. Squirrels are first attested in the [[Eocene]], about forty million years ago, and are most closely related to the [[mountain beaver]] and to the [[dormouse|dormice]] among living species.

== Etymology ==

The word ''squirrel'', first attested in 1327, comes via [[Anglo-Norman language|Anglo-Norman]] ''esquirel'' from the [[Old French]] ''escurel'', the reflex of a [[Latin language|Latin]] word ''sciurus''. This Latin word was itself borrowed from [[Ancient Greek language|Ancient Greek]] word σκίουρος, ''skiouros'', which means shadow-tailed, referring to the bushy appendage possessed by many of its members.<ref>{{cite encyclopedia | encyclopedia =[[The Oxford English Dictionary]] | title = squirrel, ''n.'' | url = http://dictionary.oed.com/cgi/entry/50235460 | accessdate = 8 November 2010 | edition = 2nd. | year = 1989 | publisher = Oxford University Press}}</ref><ref>Whitaker & Elman (1980): 370</ref>

The native [[Old English language|Old English]] word, ''ācweorna'', survived only into [[Middle English language|Middle English]] (as ''aquerna'') before being replaced.<ref name="etymonline">{{cite web | url=http://www.etymonline.com/index.php?term=squirrel | title=Squirrel | work=Online Etymology Dictionary | accessdate=2008-02-07}}</ref> The Old English word is of [[Common Germanic]] origin, with [[cognate]]s such as [[German language|German]] ''Eichhorn'' and [[Norwegian language|Norwegian]] ''ekorn''.

== Characteristics ==

[[File:Ratufa skull.JPG|thumb|left|Skull of an [[Oriental giant squirrel]] (genus ''Ratufa''). Note the classic [[sciuromorphous]] shape of the anterior [[zygomatic arch|zygomatic]] region.]]

Squirrels are generally small animals, ranging in size from the [[African pygmy squirrel]], at {{convert|7|-|10|cm|abbr=on}} in length, and just {{convert|10|g|abbr=on}} in weight, to the [[Alpine marmot]], which is {{convert|53|-|73|cm|abbr=on}} long, and weighs from {{convert|5|to|8|kg|abbr=on}}. Squirrels typically have slender bodies with bushy tails and large eyes. Their [[fur]] is generally soft and silky, although much thicker in some species than others. The color of squirrels is highly variable between&nbsp;– and often even within&nbsp;– species.<ref>[http://www.wildlifeonline.me.uk/squirrels.html Tree Squirrels], ''Wildlife Online'', 23 November 2010.</ref>

The hindlimbs are generally longer than the forelimbs, and they have four or five toes on each foot. Their paws on their forefeet include a [[thumb]], although this is often poorly developed. The feet also have a soft pad on the underside.<ref name=EoM>Milton (1984)</ref>

Squirrels live in almost every habitat from tropical [[rainforest]] to semiarid [[desert]], avoiding only the high polar regions and the driest of deserts. They are predominantly [[herbivore|herbivorous]], subsisting on seeds and nuts, but many will eat insects, and even small vertebrates.{{citation needed|date=November 2010}}

As their large eyes indicate, squirrels generally have an excellent sense of [[Visual perception|vision]], which is especially important for tree-dwelling species. They also have very versatile and sturdy [[claws]] for grasping and [[tree climbing|climbing]].<ref>[http://animals.howstuffworks.com/mammals/squirrel-info.htm "Squirrel" - HowStuffWorks]</ref> Many also have a good sense of [[somatosensory system|touch]], with [[vibrissa]]e on their heads and limbs.<ref name=EoM/>

The teeth of sciurids follow the typical rodent pattern, with large gnawing [[incisor]]s that grow throughout life, and grinding cheek teeth set back behind a wide gap, or [[diastema (dentistry)|diastema]]. The typical [[dentition|dental formula]] for sciurids is {{DentalFormula|upper=1.0.1.3|lower=1.0.1.3}}

== Behavior ==

[[File:blacksquirrelrev.jpg|thumb|250px|right|Several species of squirrels have [[melanism|melanistic]] phases. In large parts of United States and Canada, the most common variety seen in urban areas is the melanistic form of the [[Eastern Gray Squirrel]].]]

[[File:Squirrel Eating a peanut.jpg|thumb|250px|right|Squirrel eating a peanut]]

Squirrels breed once or twice a year, and give birth to a varying number of young after three to six weeks, depending on species. The young are born naked, toothless, helpless, and blind. In most species of squirrel, only the female looks after the young, which are [[weaning|weaned]] at around six to ten weeks of age and become sexually mature at the end of their first year. Ground dwelling species are generally social animals, often living in well-developed colonies, but the tree-dwelling species are more solitary.<ref name=EoM/>

Ground and tree squirrels are typically [[Diurnality|diurnal]], while flying squirrels tend to be [[Nocturnality|nocturnal]]—except for lactating flying squirrels and their offspring which have a period of diurnality during the summer.<ref>{{cite journal | last=Törmälä | first=Timo | coauthors=Vuorinen, Hannu; Hokkanen, Heikki | year=1980 | title=Timing of circadian activity in the flying squirrel in central Finland | journal=Acta Theriologica | volume=25 | issue=32–42 | pages=461–474 | url=http://acta.zbs.bialowieza.pl/contents/?art=1980-025-32-42-0461 | accessdate=11 July 2007}}</ref>

=== Feeding ===

[[File:Indian Palm Squirrel Bangalore 2009.jpg|thumb|250px| The [[Indian Palm Squirrel]] is the most common type of squirrel found in India.]]

Unlike [[rabbit]]s or [[deer]], squirrels cannot feed upon [[cellulose]] and must rely on foods rich in [[protein]], [[carbohydrates]], and [[fat]]. In temperate regions, early spring is the hardest time of year for squirrels, because buried nuts begin to sprout and are no longer available for the squirrel to eat, and new food sources have not become available yet. During these times squirrels rely heavily on the buds of trees. Squirrels' diet consists primarily of a wide variety of plant food, including [[nut (fruit)|nut]]s, [[seed]]s, [[conifer cone]]s, [[fruit]]s, [[fungus|fungi]] and green [[vegetation]]. However some squirrels also consume meat, especially when faced with hunger.<ref>[http://www.squirrels.org/faq.html Squirrel Place] - squirrels.org - Retrieved 14 December 2010.</ref> Squirrels have been known to eat [[insect]]s, eggs, small [[bird]]s, young [[snake]]s and smaller [[rodent]]s. Indeed, some tropical species have shifted almost entirely to a diet of insects.<ref>Richard W. Thorington, Katie Ferrell - [http://books.google.com/books?id=Y7cuEWCWpLMC&pg=PA75&lpg=PA75&dq=some+tropical+squirrels+eat+almost+only+insects&source=bl&ots=8Mq7YGqzSL&sig=xszWl76FS4tJHB5oULDExUapN3A&hl=en&ei=BB4HTeuoCIep8AbG5_SFCg&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCEQ6AEwAg#v=onepage&q&f=false ''Squirrels: the animal answer guide''], JHU Press, 2006, ISBN 0801884020, 9780801884023, p. 75.</ref>

Predatory behavior by various species of ground squirrels, particularly the [[thirteen-lined ground squirrel]], has been noted.<ref>{{cite journal | last=Friggens | first=M. | coauthors= | title=Carnivory on Desert Cottontails by Texas Antelope Ground Squirrels | url=http://jstor.org/stable/3672818 | journal=The Southwestern Naturalist | volume=47 | issue=1 | pages=132–133 | year=2002 | doi=10.2307/3672818}}</ref> For example, Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young chicken.<ref>{{cite journal | last=Bailey | first=B. | title=Meat-eating propensities of some rodents of Minnesota | journal=Journal of Mammalogy | volume=4 | issue= | page=129 | month= | year=1923 | url= | accessdate=}}</ref> Wistrand reported seeing this same species eating a freshly killed snake.<ref>{{cite journal | last=Wistrand | first=E.H. | coauthors= | title=Predation on a Snake by ''Spermophilus tridecemlineatus'' | url=http://jstor.org/stable/2424389 | journal=American Midland Naturalist | volume=88 | issue=2 | pages=511–512 | year=1972 | doi=10.2307/2424389}}</ref> Whitaker examined the stomachs of 139 thirteen-lined ground squirrels, and found bird flesh in four of the specimens and the remains of a short-tailed [[shrew]] in one;<ref>{{cite journal | last=Whitaker | first=J.O. | title=Food and external parasites of ''Spermophilus tridecemlineatus'' in Vigo County, Indiana | url=http://jstor.org/stable/1379067 | journal=Journal of Mammalogy | volume=53 | issue=3 | pages=644–648 | year=1972 | doi=10.2307/1379067}}</ref> Bradley, examining [[white-tailed antelope squirrel]]s' stomachs, found at least 10% of his 609 specimens' stomachs contained some type of vertebrate, mostly [[lizard]]s and rodents.<ref>{{cite journal | last=Bradley | first=W. G. | coauthors= | title=Food habits of the antelope ground squirrel in southern Nevada | url=http://jstor.org/stable/1377723 | journal=Journal of Mammalogy | volume=49 | issue=1 | pages=14–21 | doi=10.2307/1377723 | year=1968}}</ref> Morgart (1985) observed a white-tailed antelope squirrel capturing and eating a [[Perognathus|silky pocket mouse]].<ref>{{cite journal | last=Morgart | first=J. R. | coauthors= | title=Carnivorous behavior by a white-tailed antelope ground squirrel ''Ammospermophilus leucurus'' | url=http://jstor.org/stable/3670745 | journal=The Southwestern Naturalist | volume=30 | issue=2 | pages=304–305 | doi=10.2307/3670745 | month=May | year=1985}}</ref>

== Taxonomy ==

[[File:Giant-squirrel.jpg|thumb|right|[[Grizzled Giant Squirrel]] (''Ratufa macroura'') of the [[Ratufinae]]]]

[[File:Jill Flying 1.jpg|thumb|right|[[Southern Flying Squirrel]] (''Glaucomys volans'') of the [[Pteromyini]]]]

[[File:Schoenhoernchen Callosciurus prevosti.jpg|thumb|right|[[Prevost's Squirrel]] (''Callosciurus prevosti'') of the [[Callosciurini]]]]

[[File:Xerus rutilus.jpg|thumb|right|[[Unstriped Ground Squirrel]] (''Xerus rutilus'') of the [[Xerini]]]]

[[File:Marmot in France.jpg|thumb|right|[[Alpine Marmot]] (''Marmota marmota'') of the [[Marmotini]]]]

[[File:Baby Squirrel Sleeping.jpg|thumb|right|A baby squirrel sleeping.]]

The living squirrels are divided into five [[subfamilies]], with about 50 [[genera]] and nearly 280 [[species]]. The oldest squirrel fossil, ''[[Hesperopetes]]'', dates back to the [[Chadronian]] (Late [[Eocene]], about 40–35 [[million years ago]]), and is similar to modern flying squirrels.<ref>{{cite journal|doi=10.1671/0272-4634(2007)27[693:ANGOSR]2.0.CO;2|last=Emry|first=R. J.|last2=Korth|first2= W.W. |year=2007|title= A new genus of squirrel (Rodentia, Sciuridae) from the mid-Cenozoic of North America|journal= Journal of Vertebrate Paleontology |volume=27|issue=3|pages=693&ndash;698}}</ref>

During the latest Eocene to the [[Miocene]], there were a variety of squirrels which cannot be assigned with certainty to any living lineage. At least some of these probably were variants of the oldest, [[basal (evolution)|basal]] "[[proto-|proto]]-squirrels" (in the sense that they lacked the full range of living squirrels' [[autapomorphy|autapomorphies]]). The distribution and diversity of such ancient and ancestral forms suggests that the squirrels as a group might have originated in North America.<ref name = tolweb>Steppan & Hamm (2006)</ref>

Apart from these sometimes little-known fossil forms, the [[phylogeny]] of the living squirrels is fairly straightforward. There are three main lineages, one comprising the [[Ratufinae]] (Oriental giant squirrels). These contain a mere handful of living species in tropical [[Asia]]. The [[Neotropical Pygmy Squirrel]] of tropical [[South America]] is the sole living member of the Sciurillinae. The third lineage is by far the largest and contains all other subfamilies; it has a near-cosmopolitan distribution. This further supports the hypothesis that the common ancestor of all squirrels living and fossil lived in North America, as these three most ancient lineages seem to have [[evolutionary radiation|radiated]] from there&nbsp;– if squirrels had originated in Eurasia for example, one would expect quite ancient lineages in [[Africa]], but African squirrels seem to be of more recent origin.<ref name = tolweb />

The main group of squirrels also can be split up in three, which yields the remaining subfamilies. The [[Sciurinae]] contains the [[flying squirrel]]s (Pteromyini) and the [[Sciurini]], which among others contains the American tree squirrels; the former have often been considered a separate subfamily but are now seen as a [[tribe (biology)|tribe]] of the Sciurinae. The [[pine squirrel]]s (''Tamiasciurus'') on the other hand are usually included with the main tree squirrel lineage, but appear to be about as distinct as the flying squirrels; hence they are sometimes considered a distinct tribe, Tamiasciurini.<ref>Steppan ''et al.'' (2004), Steppan & Hamm (2006)</ref>

Be that as it may, the three-way split of the main squirrel lineage is rather neat from a [[biogeographical]] and [[ecological]] perspective. Two of the three subfamilies are of about equal size, containing between nearly 70 to some 80 species each; the third is about twice as large. The Sciurinae contains arboreal (tree-living) squirrels, mainly of the Americas and to a lesser extent Eurasia. The [[Callosciurinae]] on the other hand is most diverse in tropical Asia and contains squirrels which are also arboreal, but have a markedly different [[Morphology (biology)|habitus]] and appear more "elegant", an effect enhanced by their often very colorful fur. The [[Xerinae]]&nbsp;– the largest subfamily&nbsp;– are made up from the mainly terrestrial (ground-living) forms and include the large [[marmot]]s and the popular [[prairie dog]]s among others, as well as the tree squirrels of Africa; they tend to be more gregarious than other squirrels which do not usually live together in close-knit groups.<ref name = tolweb />

*[[Basal (evolution)|Basal]] and ''[[incertae sedis]]'' Sciuridae (all [[fossil]])

**''[[Hesperopetes]]''

**''[[Kherem]]''

**''[[Lagrivea]]''

**''[[Oligosciurus]]''

**''[[Plesiosciurus]]''

**''[[Prospermophilus]]''

**''[[Sciurion]]''

**''[[Similisciurus]]''

**''[[Sinotamias]]''

**''[[Vulcanisciurus]]''

*Subfamily [[Cedromurinae]] (fossil)

*Subfamily [[Ratufinae]] – Oriental giant squirels (1 genus, 4 species)

*Subfamily [[Sciurillinae]] – Neotropical Pygmy Squirrel ([[monotypic]])

*Subfamily [[Sciurinae]]

**Tribe [[Sciurini]] – tree squirrels (5 genera, c.38 species)

**Tribe [[Pteromyini]] – true flying squirrels (15 genera, c.45 species)

*Subfamily [[Callosciurinae]] – Asian ornate squirrels

**Tribe [[Callosciurini]] (13 genera, nearly 60 species)

**Tribe [[Funambulini]] palm squirrels (1 genus, 5 species)

*Subfamily [[Xerinae]] – terrestrial squirrels

**Tribe [[Xerini]] – spiny squirrels (3 genera, 6 species)

**Tribe [[Protoxerini]] (6 genera, c.50 species)

**Tribe [[Marmotini]] – ground squirrels, marmots, chipmunks, prairie dogs, etc. (6 genera, c.90 species)

== References ==

{{reflist|colwidth=30em}}

== Literature cited ==

* Milton, Katherine (1984): [Family Sciuridae]. ''In:'' Macdonald, D. (ed.): ''The Encyclopedia of Mammals'': 612–623. Facts on File, New York. ISBN 0-87196-871-1

* Steppan, Scott J. & Hamm, Shawn M. (2006): [[Tree of Life Web Project]] – [http://tolweb.org/Sciuridae/16456/2006.05.13 Sciuridae (Squirrels)]. Version of 13 May 2006. Retrieved 10 December 2007.

* Steppan, Scott J.; Storz, B.L. & Hoffmann, R.S. (2004): [http://bio.fsu.edu/~steppan/Steppan_et_al_Sciuridae.pdf "Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1" (pdf)]. ''[[Molecular Phylogenetics and Evolution|Mol. Phyl. Evol.]]'' '''30'''(3): 703–719. {{doi|10.1016/S1055-7903(03)00204-5}}

* Thorington, R.W. & Hoffmann, R.S. (2005): Family Sciuridae. ''In: Mammal Species of the World – A Taxonomic and Geographic Reference'': 754–818. Johns Hopkins University Press, Baltimore.

* Whitaker, John O. Jr. & Elman, Robert (1980): ''The Audubon Society Field Guide to North American Mammals'' (2nd ed.). [[Alfred Knopf]], New York. ISBN 0-394-50762-2

== External links ==

{{Commons|Sciuridae}}

{{wikispecies|Sciuridae}}

{{wiktionary|squirrel}}

* [http://tolweb.org/Sciuridae/16456 Tree of Life: Sciuridae]

* [http://northernbushcraft.com/animalTracks/squirrel/notes.htm Squirrel Tracks]: How to identify squirrel tracks in the wild

* [http://animals.nationalgeographic.com/animals/mammals/squirrel.html National Geographic link on Squirrels]

*[http://www.webcitation.org/query?url=http://www.geocities.com/yosemite/rapids/4362/sqrlenc.html&date=2009-10-26+00:29:13 Andrew's Squirrel Encyclopaedia]

*[http://www.squirrels.org/names.html List of names of squirrel taxa]

{{Rodents}}

{{S. Ratufinae-Sciurillinae nav}}

{{S. Callosciurinae nav}}

{{S. Sciurinae1 nav}}

{{S. Sciurinae2 nav}}

{{S. Xerinae nav}}

{{Marmotini nav}}

[[Category:Rodents]]

[[Category:Squirrels| ]]

[[af:Eekhoring]]

[[ang:Ācƿeorna]]

[[ar:سنجابيات]]

[[an:Sciuridae]]

[[roa-rup:Ververa]]

[[ast:Esguilu]]

[[az:Sincablar]]

[[bn:কাঠবিড়ালী]]

[[zh-min-nan:Phòng-chhí]]

[[be:Вавёркавыя]]

[[be-x-old:Вавёркавыя]]

[[bo:ནགས་བྱི།]]

[[br:Sciuridae]]

[[bg:Катерицови]]

[[ca:Esciúrid]]

[[cs:Veverkovití]]

[[cy:Gwiwer]]

[[da:Egern]]

[[de:Hörnchen]]

[[nv:Hazéí]]

[[et:Oravlased]]

[[el:Σκίουρος]]

[[myv:Ур]]

[[es:Sciuridae]]

[[eo:Sciuredoj]]

[[eu:Esziurido]]

[[fa:سنجاب]]

[[fr:Sciuridae]]

[[ga:Iora]]

[[gv:Fiorag]]

[[gl:Esquío]]

[[ko:다람쥐과]]

[[hi:गिलहरी]]

[[hr:Vjeverice]]

[[io:Skurelo]]

[[id:Bajing]]

[[os:Æхсæрсæттæг]]

[[it:Sciuridae]]

[[he:סנאיים]]

[[kn:ಅಳಿಲು]]

[[kbd:КӀэпхъ]]

[[ka:ციყვისებრნი]]

[[kk:Тиіндер]]

[[kv:Ур]]

[[ku:Sihorîk]]

[[la:Sciurus]]

[[lv:Vāveres]]

[[lb:Kaweechelcher]]

[[lt:Voveriniai]]

[[hu:Mókusfélék]]

[[mk:Верверици]]

[[ml:അണ്ണാൻ]]

[[mr:खार]]

[[ms:Tupai]]

[[my:ရှဉ့်]]

[[nl:Eekhoorns]]

[[nds-nl:Kateker]]

[[ja:リス]]

[[ce:Тарсал]]

[[no:Ekornfamilien]]

[[nn:Ekornfamilien]]

[[nrm:Jaqùet]]

[[oc:Sciuridae]]

[[mhr:Ур]]

[[pnb:گالڑ]]

[[pap:Djaca di caña]]

[[pl:Wiewiórkowate]]

[[pt:Esquilo]]

[[ro:Veveriță]]

[[ru:Беличьи]]

[[sah:Тииҥниҥилэр кэргэннэрэ]]

[[sq:Ketri]]

[[sl:Prave veverice]]

[[srn:Ekosi]]

[[sr:Веверица]]

[[su:Bajing]]

[[fi:Oravat]]

[[sv:Ekorrar]]

[[tl:Iskwirel]]

[[ta:அணில்]]

[[te:ఉడుత]]

[[th:กระรอก]]

[[chy:No'kéeho]]

[[tr:Sincap]]

[[uk:Вивіркові]]

[[vi:Họ Sóc]]

[[zh:松鼠]]