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Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Megaclassis: Osteichthyes
Cladus: Sarcopterygii
Cladus: Rhipidistia
Cladus: Tetrapodomorpha
Cladus: Eotetrapodiformes
Cladus: Elpistostegalia
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Cladus: Synapsida
Cladus: Eupelycosauria
Cladus: Sphenacodontia
Cladus: Sphenacodontoidea
Cladus: Therapsida
Cladus: Theriodontia
Subordo: Cynodontia
Infraordo: Eucynodontia
Cladus: Probainognathia
Cladus: Prozostrodontia
Cladus: Mammaliaformes
Classis: Mammalia
Subclassis: Trechnotheria
Infraclassis: Zatheria
Supercohors: Theria
Cohors: Eutheria
Infraclassis: Placentalia
Cladus: Boreoeutheria
Superordo: Euarchontoglires
Ordo: Rodentia
Subordo: Sciuromorpha

Familia: Sciuridae
Subfamiliae (5): NannosciurinaeRatufinaeSciurinaeSciurillinaeXerinae


Sciuridae Fischer von Waldheim, 1817: 408

Sciuridae in Mammal Species of the World.
Wilson, Don E. & Reeder, DeeAnn M. (Editors) 2005. Mammal Species of the World – A Taxonomic and Geographic Reference. Third edition. ISBN 0-8018-8221-4.

Vernacular names
Akan: Opro
беларуская: Вавёркавыя
বাংলা: কাঠবিড়ালী
català: Esciúrid
Tsetsêhestâhese: No'kéeho
čeština: Veverkovití
English: Squirrel
Esperanto: Sciuro
español: Ardilla
suomi: Orava
français: Ecureuil
Gaeilge: Iora
հայերեն: Սկյուռներ
한국어: 다람쥐과
ဘာသာ မန်: ပြိပ်၊ ယန်၊ သၞ။
မြန်မာဘာသာ: ရှဉ့်
Diné bizaad: Hazéí
polski: Wiewiórkowate
slovenščina: Veverica
ไทย: กระรอก
Türkçe: Sincapgiller
中文: 松鼠科

Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrels. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were introduced by humans to Australia.[1] The earliest known fossilized squirrels date from the Eocene epoch, and among other living rodent families, the squirrels are most closely related to the mountain beaver and to the dormice.

The word squirrel, first attested in 1327, comes from the Anglo-Norman esquirel which is from the Old French escurel, the reflex of a Latin word sciurus, which was taken from the Ancient Greek word σκίουρος (skiouros; from σκία-ουρος) 'shadow-tailed', referring to the long bushy tail which many of its members have.[2][3]

The native Old English word for the squirrel, ācweorna, survived only into Middle English (as aquerne) before being replaced.[4] The Old English word is of Common Germanic origin, cognates of which are still used in other Germanic languages, including the German Eichhörnchen (diminutive of Eichhorn, which is not as frequently used), the Norwegian ikorn/ekorn, the Dutch eekhoorn, the Swedish ekorre and the Danish egern.

A group of squirrels is called a "dray"[5] or a "scurry".[6]
Reaching out for food on a garden bird feeder, this squirrel can rotate its hind feet, allowing it to descend a tree head-first.
Skull of an Oriental giant squirrel (genus Ratufa)—note the classic sciuromorphous shape of the anterior zygomatic region.

Squirrels are generally small animals, ranging in size from the African pygmy squirrel and least pygmy squirrel at 10–14 cm (3.9–5.5 in) in total length and just 12–26 g (0.42–0.92 oz) in weight,[7][8] to the Bhutan giant flying squirrel at up to 1.27 m (4 ft 2 in) in total length,[9] and several marmot species, which can weigh 8 kg (18 lb) or more.[10][11] Squirrels typically have slender bodies with very long very bushy tails and large eyes. In general, their fur is soft and silky, though much thicker in some species than others. The coat color of squirrels is highly variable between—and often even within—species.[12]

In most squirrel species, the hind limbs are longer than the fore limbs, while all species have either four or five toes on each foot. The feet, which include an often poorly developed thumb, have soft pads on the undersides[13] and versatile, sturdy claws for grasping and climbing.[14] Tree squirrels, unlike most mammals, can descend a tree head-first. They do so by rotating their ankles 180 degrees, enabling the hind feet to point backward and thus grip the tree bark from the opposite direction.[15]

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 herbivorous, subsisting on seeds and nuts, but many will eat insects and even small vertebrates.[16]

As their large eyes indicate, squirrels have an excellent sense of vision, which is especially important for the tree-dwelling species. Many also have a good sense of touch, with vibrissae on their limbs as well as their heads.[13]

The teeth of sciurids follow the typical rodent pattern, with large incisors (for gnawing) that grow throughout life, and cheek teeth (for grinding) that are set back behind a wide gap, or diastema. The typical dental formula for sciurids is[17]

Many juvenile squirrels die in the first year of life. Adult squirrels can have a lifespan of 5 to 10 years in the wild. Some can survive 10 to 20 years in captivity.[18] Premature death may occur when a nest falls from the tree, in which case the mother may abandon her young if their body temperature is not correct. Many such baby squirrels have been rescued and fostered by a professional wildlife rehabilitator until they could be safely returned to the wild,[19] although the density of squirrel populations in many places and the constant care required by premature squirrels means that few rehabilitators are willing to spend their time doing this and such animals are routinely euthanized instead.

Stated purposes of squirrels' tails, to benefit the squirrel, include:[20]

To keep rain, wind, or cold off itself.
To cool off when hot, by pumping more blood through its tail.
As a counterbalance when jumping about in trees.
As a parachute when jumping.
To signal with.

The hairs from squirrel tails are prized in fly fishing when tying fishing flies. A special quality of squirrel tail hair is that it is all guard hairs, not undercoat.

When the squirrel sits upright, its tail folded up its back may stop predators looking from behind from seeing the characteristic shape of a small mammal.

Young squirrels

Squirrels mate either once or twice a year and, following a gestation period of three to six weeks, give birth to a number of offspring that varies by species. The young are altricial, being born naked, toothless, and blind. In most species of squirrel, the female alone looks after the young, which are weaned at six to ten weeks and become sexually mature by the end of their first year. In general, the ground-dwelling squirrel species are social, often living in well-developed colonies, while the tree-dwelling species are more solitary.[13]

Ground squirrels and tree squirrels are usually either diurnal or crepuscular,[21] while the flying squirrels tend to be nocturnal—except for lactating flying squirrels and their young, which have a period of diurnality during the summer.[22]
Squirrel eating a fruit in Manyara National Park, Tanzania
Red squirrel in the Seurasaari island in Helsinki, Finland. The tame red squirrels on that island have become accustomed to humans thanks to their long-term feeding.[23]

Because squirrels cannot digest cellulose, they must rely on foods rich in protein, carbohydrates, and fats. In temperate regions, early spring is the hardest time of year for squirrels because the nuts they buried are beginning to sprout (and thus are no longer available to eat), while many of the usual food sources are not yet available. During these times, squirrels rely heavily on tree buds. Squirrels, being primarily herbivores, eat a wide variety of plants, as well as nuts, seeds, conifer cones, fruits, fungi, and green vegetation. Some squirrels, however, also consume meat, especially when faced with hunger.[16][24] Squirrels have been known to eat small birds, young snakes, and smaller rodents, as well as bird eggs and insects. Some tropical squirrel species have shifted almost entirely to a diet of insects.[25]

Squirrels, like pigeons and other fauna, are synanthropes, in that they benefit and thrive from their interaction in human environments. This gradual process of successful interaction is called synurbanization, wherein squirrels lose their inherent fear of humans in an urban environment.[26] When squirrels were almost completely eradicated during the Industrial Revolution in New York, they were later re-introduced to "entertain and remind" humans of nature. The squirrel blended into the urban environment so efficiently that when synanthropic behavior stops (i.e. people do not leave trash outside during particularly cold winters), they can become aggressive in their search for food.

Aggression and predatory behavior has been observed in various species of ground squirrels, in particular the thirteen-lined ground squirrel.[27] For example, Bernard Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young chicken.[28] Wistrand reported seeing this same species eating a freshly killed snake.[29] There has also been at least one report of squirrels preying on atypical animals, such as an incident in 2005 where a pack of black squirrels killed and ate a large stray dog in Lazo, Russia.[30] Squirrel attacks on humans are exceedingly rare, but do occur.[31][32]

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;[33] Bradley, examining the stomachs of white-tailed antelope squirrels, found at least 10% of his 609 specimens' stomachs contained some type of vertebrate, mostly lizards and rodents.[34] Morgart observed a white-tailed antelope squirrel capturing and eating a silky pocket mouse.[35]
Squirrel (Sciurus niger) outside the Cleveland Museum of Art
A squirrel (Callosciurus erythraeus thaiwanensis) in Japan
Three-coloured Prevost's Squirrel (Callosciurus prevostii) in Zagreb Zoo, Croatia

The living squirrels are divided into five subfamilies, with about 58 genera and some 285 species.[36] 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.[37]

A variety of fossil squirrels, from the latest Eocene to the Miocene, have not been assigned with certainty to any living lineage. At least some of these probably were variants of the oldest basal "protosquirrels" (in the sense that they lacked the full range of living squirrels' autapomorphies). The distribution and diversity of such ancient and ancestral forms suggest the squirrels as a group may have originated in North America.[38]

Apart from these sometimes little-known fossil forms, the phylogeny of the living squirrels is fairly straightforward. The three main lineages are the Ratufinae (Oriental giant squirrels), Sciurillinae and all other subfamilies. The Ratufinae 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, by far the largest, 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 radiated from there; 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.[38]

The main group of squirrels can be split into five subfamilies. The Callosciurinae, 60 species mostly found in South East Asia; the Ratufinae 4 cat-sized species found in south and southeast Asia; the Sciurinae contains the flying squirrels (Pteromyini) and the tree squirrels, 83 species found world wide;[39] Sciurillinae a single South American species; and Xerinae includes three tribes of mostly terrestrial squirrels, including the Marmotini (marmots, chipmunks, prairie dogs, and other Holarctic ground squirrels), Xerini (African and some Eurasian ground squirrels), and Protoxerini (African tree squirrels).
Taxonomy list

Basal and incertae sedis Sciuridae (all fossil)
Subfamily Cedromurinae (fossil)
Subfamily Ratufinae – Oriental giant squirrels (1 genus, 4 species)
Subfamily Sciurillinae – neotropical pygmy squirrel (monotypic)
Subfamily Sciurinae
Tribe Sciurini – tree squirrels (5 genera, about 38 species)
Tribe Pteromyini – true flying squirrels (15 genera, about 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, about 50 species)
Tribe Marmotini – ground squirrels, marmots, chipmunks, prairie dogs, etc. (6 genera, about 90 species)


Squirrels are a cause for concern because they often cause electrical disruptions. It has been hypothesized that the threat to the internet, infrastructure and services posed by squirrels may exceed that posed by cyber-attacks.[40]
See also

American red squirrel
Animal track
Black squirrel
Eastern gray squirrel
Fox squirrel
List of animal names#squirrel
Red squirrel
Squirrel relationship with humans
Variant Creutzfeldt–Jakob disease (Kuru) from eating squirrel brains.[41][42]
Western gray squirrel


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Merja Laavola: Eläinten elintasosairaudet näkyvät Seurasaaressa. Vartti Etelä-Helsinki, Sanoma Kaupunkilehdet, 2010. (in Finnish)
"Russian squirrel pack 'kills dog'". 1 December 2005. Retrieved 13 July 2018.
Richard W. Thorington, Katie Ferrell – Squirrels: the animal answer guide, JHU Press, 2006, ISBN 0-8018-8402-0, ISBN 978-0-8018-8402-3, p. 75.
Peiman, Kathryn (June 2016). "Sublethal consequences of urban life for wild vertebrates". Environmental Reviews. 24 (4): 416–425. doi:10.1139/er-2016-0029. hdl:1807/74036.
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Rettner, Rachael (15 October 2018). "Man Dies from Extremely Rare Disease After Eating Squirrel Brains". LiveScience. Retrieved 9 April 2022.

Further reading

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. and Hamm, Shawn M. (2006): Tree of Life Web Project – "Sciuridae (Squirrels)". Version of 13 May 2006. Retrieved 10 December 2007.
Steppan, S. J.; Storz, B. L.; Hoffmann, R. S. (2004). "Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1". Molecular Phylogenetics and Evolution. 30 (3): 703–719. doi:10.1016/S1055-7903(03)00204-5. PMID 15012949.
Thorington, R.W. and 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. and Elman, Robert (1980): The Audubon Society Field Guide to North American Mammals (2nd ed.). Alfred Knopf, New York. ISBN 0-394-50762-2

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