family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

tree squirrel Tree squirrels are the members of the squirrel Family (biology), family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a ...

ground squirrel Ground squirrels are rodents of the squirrel family (Sciuridae) that generally live on the ground or in burrows, rather than in trees like the tree squirrels. The term is most often used for the medium-sized ground squirrels, as the larger ones ar ...

chipmunk Chipmunks are small, striped rodents of subtribe Tamiina. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks are classified as four genera: '' ...

prairie dog Prairie dogs (genus ''Cynomys'') are herbivorous burrowing Marmotini, ground squirrels native to the grasslands of North America. There are five recognized species of prairie dog: black-tailed prairie dog, black-tailed, white-tailed prairie dog ...

flying squirrel Flying squirrels (scientifically known as Pteromyini or Petauristini) are a tribe (biology), tribe of 50 species of squirrels in the family (biology), family Squirrel, Sciuridae. Despite their name, they are not in fact capable of full flight i ...

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

mountain beaver The mountain beaver (''Aplodontia rufa'')Other names include boomer, mountain boomer, ground bear, giant mole, gehalis, sewellel, suwellel, showhurll, showtl, and showte, as well as a number of other Native American terms. "Mountain beaver" is a ...

dormice A dormouse is a rodent of the family (biology), family Gliridae (this family is also variously called Myoxidae or Muscardinidae by different taxonomists). Dormice are nocturnal animals found in Africa, Asia, and Europe. They are named for their ...

Old French Old French (, , ; ) was the language spoken in most of the northern half of France approximately between the late 8th

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word , which was taken from the Ancient Greek word (; from ) 'shadow-tailed', referring to the long bushy tail which many of its members have. ''Sciurus'' is also the name of one of its genuses. The native Old English language, Old English word for the squirrel, , only survived into Middle English language, Middle English (as ) before being replaced. The Old English word is of

Common Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic bra ...

origin,

cognate In historical linguistics, cognates or lexical cognates are sets of words that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical effects on both the s ...

s of which are still used in other

Germanic languages The Germanic languages are a branch of the Indo-European languages, Indo-European language family spoken natively by a population of about 515 million people mainly in Europe, North America, Oceania, and Southern Africa. The most widely spoke ...

, including the

German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...

(diminutive of , which is not as frequently used); the Norwegian /; the

Dutch Dutch or Nederlands commonly refers to: * Something of, from, or related to the Netherlands ** Dutch people as an ethnic group () ** Dutch nationality law, history and regulations of Dutch citizenship () ** Dutch language () * In specific terms, i ...

; the Swedish and the Danish . A group of squirrels is called a "dray" or a "scurry".

Characteristics

Squirrels are generally small animals, ranging in size from the African pygmy squirrel and least pygmy squirrel at in total length and just in weight, to the

Bhutan giant flying squirrel The Bhutan giant flying squirrel (''Petaurista nobilis''), also known as the Gray's giant flying squirrel or noble giant flying squirrel, is a species of rodent in the family Sciuridae. This species lives in Himalayan forests and it is one of th ...

at up to in total length, and several

marmot Marmots are large ground squirrels in the genus ''Marmota'', with 15 species living in Asia, Europe, and North America. These herbivores are active during the summer, when they can often be found in groups, but are not seen during the winter, w ...

species, which can weigh or more. Squirrels typically have slender bodies with long, bushy tails and large eyes. In general, their

fur A fur is a soft, thick growth of hair that covers the skin of almost all mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an ...

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. In most squirrel species, the hind limbs are longer than the forelimbs, while all species have either four or five toes on each foot. The feet, which include an often poorly developed

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

, have soft pads on the undersidesMilton (1984) and versatile, sturdy

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or Arthro ...

s for grasping and

climbing Climbing is the activity of using one's hands, feet, or other parts of the body to ascend a steep topographical object that can range from the world's tallest mountains (e.g. the eight thousanders) to small boulders. Climbing is done for locom ...

.

Tree squirrels Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a single natural, or ...

, unlike most mammals, can descend a tree headfirst. 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.

Head

As their large eyes indicate, squirrels have excellent

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

, which is especially important for the tree-dwelling species. Many also have a good sense of

touch The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bo ...

, with

vibrissae Whiskers, also known as vibrissae (; vibrissa; ) are a type of stiff, functional hair used by most therian mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser as t ...

on their limbs as well as their heads. The teeth of sciurids follow the typical rodent pattern, with large

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s (for gnawing) that grow throughout life, and cheek teeth (for grinding) that are set back behind a wide gap, or

diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...

. The typical

dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

for sciurids is .

Tail

The purposes of squirrels' tails, to benefit the squirrel, include: * 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 A parachute is a device designed to slow an object's descent through an atmosphere by creating Drag (physics), drag or aerodynamic Lift (force), lift. It is primarily used to safely support people exiting aircraft at height, but also serves va ...

when jumping. * To signal with. The hairs from squirrel tails are prized in

fly fishing Fly fishing is an angling technique that uses an ultra-lightweight lure called an artificial fly, which typically mimics small invertebrates such as flying and aquatic insects to attract and catch fish. Because the mass of the fly lure is in ...

when tying fishing flies. Squirrel hair is very fine, making it better for tying fishing flies. 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.

Lifetime

Squirrels live in almost every habitat, from tropical

rainforest Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...

to semiarid

desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...

, avoiding only the high

polar Polar may refer to: Geography * Geographical pole, either of the two points on Earth where its axis of rotation intersects its surface ** Polar climate, the climate common in polar regions ** Polar regions of Earth, locations within the polar circ ...

regions and the driest of deserts. They are predominantly

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

, subsisting on seeds and nuts, but many will eat

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

and even small vertebrates.Squirrel Place
. squirrels.org. Retrieved 14 December 2010. 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. 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, 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 Animal euthanasia (euthanasia from ; "good death") is the act of killing an animal humanely, most commonly with injectable drugs. Reasons for euthanasia include incurable (and especially painful) conditions or diseases, lack of resources to con ...

instead. File:Squirrel enjoying in the sun.jpg, Squirrel in sunlight File:Squirrel in Chandigarh.jpg, Squirrel in

Chandigarh Chandigarh is a city and union territory in northern India, serving as the shared capital of the states of Punjab and Haryana. Situated near the foothills of the Shivalik range of Himalayas, it borders Haryana to the east and Punjab in the ...

File:Squirrel near Chandigarh.jpg, Squirrel near Chandigarh File:Squirrel on mango tree.jpg, Squirrel on

mango tree ''Mangifera indica'', commonly known as mango, is an evergreen species of flowering plant in the family Anacardiaceae. It is a large fruit tree, capable of growing to a height and width of . There are two distinct genetic populations in modern ma ...

Behavior

Squirrels mate either once or twice a year and, following a

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregn ...

period of three to six weeks, give birth to a number of offspring that varies by species. The young are

altricial Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. Altricial ...

, being born naked, toothless, and blind. In most species of squirrel, the female alone looks after the young, which are

weaned Weaning is the process of gradually introducing an infant human or other mammal to what will be its adult diet while withdrawing the supply of its mother's milk. In the UK, weaning primarily refers to the introduction of solid foods at 6 mont ...

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. Ground squirrels and tree squirrels are usually either diurnal or

crepuscular In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal (active during dawn), vespertine (biology), vespertine/vespertinal (active during dusk), or both. This is distinguished from diurnalit ...

, while the flying squirrels tend to be

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

—except for lactating flying squirrels and their young, which have a period of diurnality during the summer. During hot periods, squirrels have been documented to sploot, or lay their stomachs down on cool surfaces. Squirrels, like other rodents, employ species-specific strategies to store food, buffering against periods of scarcity. In temperate regions, squirrels commonly cache nuts beneath leaf litter, inside hollow trees, or underground. However, in subtropical and humid environments, traditional caching can lead to mold growth, decomposition, or premature germination. To counteract these challenges, some squirrels, particularly in subtropical zones, hang nuts or mushrooms on tree branches. This behavior, believed to minimize fungal infections and reduce the risk of food loss, also inadvertently aids certain trees, like

Cyclobalanopsis ''Quercus'' subgenus ''Cerris'' is one of the two subgenera into which the genus ''Quercus'' was divided in a 2017 classification (the other being subgenus ''Quercus''). It contains about 140 species divided among three sections. It may be calle ...

, in expanding their range, with forgotten or dislodged nuts sprouting in new locations, influencing forest ecology. Two species of flying squirrel, the

particolored flying squirrel The particolored flying squirrel (''Hylopetes alboniger'') is a species of rodent in the family Sciuridae. It is found in Bangladesh, Bhutan, Cambodia, China, India, Laos, Myanmar, Nepal, Thailand, and Vietnam. Its natural habitat is subtropical ...

and Hainan flying squirrel aid such cacheing by carving grooves into the nuts to fix the nuts tightly between small intersecting twigs, akin to the mortise-tenon joint in carpentry.

Feeding

Because squirrels cannot digest

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

, they must rely on foods rich in

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

,

carbohydrates A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ma ...

, and

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

s. In

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

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 A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

, eat a wide variety of plants, as well as

nuts Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed * Nut (food), a dry and edible fruit or seed, including but not limited to true nuts * Nut (hardware), fastener used with a bolt Nut, NUT or Nuts may also refer to: A ...

,

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s,

conifer cone A conifer cone, or in formal botanical usage a strobilus, : strobili, is a seed-bearing organ on gymnosperm plants, especially in conifers and cycads. They are usually woody and variously conic, cylindrical, ovoid, to globular, and have sc ...

s,

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

s,

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

, and green

vegetation Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...

. Some squirrels, however, also consume meat, especially when faced with hunger. Squirrels have been known to eat small

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s, young

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

s, and smaller rodents, as well as

bird egg Bird eggs are laid by the females and range in quantity from one (as in condors) to up to seventeen (the grey partridge). Avian clutch size, Clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been ...

s and

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s. Some

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

squirrel species have shifted almost entirely to a diet of insects. Squirrels, like

pigeons Columbidae is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with small heads, relatively short necks and slender bills that in some species feature fleshy ceres. ...

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 Urban means "related to a city". In that sense, the term may refer to: * Urban area, geographical area distinct from rural areas * Urban culture, the culture of towns and cities Urban may also refer to: General * Urban (name), a list of people ...

environment. When squirrels were almost completely eradicated during the

Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...

in

New York New York most commonly refers to: * New York (state), a state in the northeastern United States * New York City, the most populous city in the United States, located in the state of New York New York may also refer to: Places United Kingdom * ...

, 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 The thirteen-lined ground squirrel (''Ictidomys tridecemlineatus''), also known as the striped gopher, leopard ground squirrel, and squinny (formerly known as the leopard-spermophile in the age of John James Audubon, Audubon), is a species of hib ...

. For example, Bernard Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young

chicken The chicken (''Gallus gallus domesticus'') is a domesticated subspecies of the red junglefowl (''Gallus gallus''), originally native to Southeast Asia. It was first domesticated around 8,000 years ago and is now one of the most common and w ...

. Wistrand reported seeing this same species eating a freshly killed

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

. 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 The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...

in Lazo, Russia. Squirrel attacks on humans are exceedingly rare, but do occur. 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 Shrews ( family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to dif ...

in one; Bradley, examining the stomachs of

white-tailed antelope squirrel The white-tailed antelope squirrel (''Ammospermophilus leucurus'') is a diurnal species of ground squirrel, scientifically classified in the order Rodentia and family Sciuridae, found in arid regions of the southwestern United States and the Ba ...

s, found at least 10% of his 609 specimens' stomachs contained some type of vertebrate, mostly

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

s and rodents. Morgart observed a white-tailed antelope squirrel capturing and eating a silky pocket mouse.

Taxonomy

The living squirrels are divided into five

subfamilies In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zool ...

, with about 58

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

and some 285

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. The oldest squirrel fossil, ''Hesperopetes'', dates back to the

Chadronian The Chadronian is a North American Land Mammal Age typically set from around 37,000,000 to 33,700,000 years BP, a period of . The Chadronian is preceded by the Duchesnean and followed by the Orellan NALMA stages. Relative to global geological c ...

(late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

, about 40–35

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

) and is similar to modern flying squirrels. A variety of fossil squirrels, from the latest

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

to the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

, 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 In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

). The distribution and diversity of such ancient and ancestral forms suggest the squirrels as a group may have originated in North America.Steppan & Hamm (2006) Apart from these sometimes little-known fossil forms, the

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

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 Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

. The neotropical pygmy squirrel of tropical

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

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 Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

, for example, one would expect quite ancient lineages in

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

, but African squirrels seem to be of more recent origin. The main group of squirrels can be split into five subfamilies: the

Callosciurinae The Callosciurinae are an Asiatic subfamily of squirrels containing over 60 species (mostly found in South East Asia) named after the genus '' Callosciurus'', which means "beautiful squirrels". Classification *Family SciuridaeThorington, R. W. ...

, 60 species mostly found in

South East Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

; the Ratufinae, 4 cat-sized species found in

south South is one of the cardinal directions or compass points. The direction is the opposite of north and is perpendicular to both west and east. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic ''*sunþa ...

and

southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

; the

Sciurinae Sciurinae () is a subfamily of squirrels (in the family Sciuridae), uniting the flying squirrels with certain related tree squirrels. Older sources place the flying squirrels in a separate subfamily (Pteromyinae) and unite all remaining sciurids i ...

, which contains the

flying squirrel Flying squirrels (scientifically known as Pteromyini or Petauristini) are a tribe (biology), tribe of 50 species of squirrels in the family (biology), family Squirrel, Sciuridae. Despite their name, they are not in fact capable of full flight i ...

s (Pteromyini) and the

tree squirrels Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a single natural, or ...

, 83 species found worldwide;

Sciurillinae The Neotropical pygmy squirrel (''Sciurillus pusillus'') is a South American species of tree squirrel, being the only living species in the genus ''Sciurillus'' and the subfamily Sciurillinae. Genetic analysis has shown it to be the sister group ...

, a single

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

n species; and

Xerinae The Xerinae comprise a subfamily of squirrels, many of which are highly terrestrial. It includes the tribes Marmotini (marmots, chipmunks, prairie dogs, and other Holarctic ground squirrels), Xerini (African and some Eurasian ground squirrels), ...

, which includes three

tribes The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

of mostly terrestrial squirrels, including the Marmotini (

marmot Marmots are large ground squirrels in the genus ''Marmota'', with 15 species living in Asia, Europe, and North America. These herbivores are active during the summer, when they can often be found in groups, but are not seen during the winter, w ...

s,

chipmunk Chipmunks are small, striped rodents of subtribe Tamiina. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks are classified as four genera: '' ...

s,

prairie dog Prairie dogs (genus ''Cynomys'') are herbivorous burrowing Marmotini, ground squirrels native to the grasslands of North America. There are five recognized species of prairie dog: black-tailed prairie dog, black-tailed, white-tailed prairie dog ...

s, and other

Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical reg ...

ground squirrels),

Xerini Xerini is a tribe of ground squirrels occurring in Africa and Asia. With the tribes Marmotini (Holarctic ground squirrels) and Protoxerini (African tree squirrels), they form the subfamily Xerinae. There are five living genera—'' Xerus'', the ...

(African and some Eurasian ground squirrels), and

Protoxerini The Protoxerini comprise a tribe of squirrels found in Africa. The 30 species in six genera are:Thorington, R. W. and R. S. Hoffmann. 2005. Family Sciuridae. Pp 754–818 in Mammal Species of the World A Taxonomic and Geographic Reference. Johns ...

(African tree squirrels).

Taxonomy list

* Basal and ''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' Sciuridae (all

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

) ** '' Hesperopetes'' ** '' Kherem'' ** '' Lagrivea'' ** '' Oligosciurus'' ** '' Plesiosciurus'' ** '' Prospermophilus'' ** '' Sciurion'' ** '' Similisciurus'' ** '' Sinotamias'' ** '' Vulcanisciurus'' * Subfamily Cedromurinae (fossil) * Subfamily Ratufinae – Oriental giant squirrels (1 genus, 4 species) * Subfamily

Sciurillinae The Neotropical pygmy squirrel (''Sciurillus pusillus'') is a South American species of tree squirrel, being the only living species in the genus ''Sciurillus'' and the subfamily Sciurillinae. Genetic analysis has shown it to be the sister group ...

– neotropical pygmy squirrel (

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

) * Subfamily

Sciurinae Sciurinae () is a subfamily of squirrels (in the family Sciuridae), uniting the flying squirrels with certain related tree squirrels. Older sources place the flying squirrels in a separate subfamily (Pteromyinae) and unite all remaining sciurids i ...

** Tribe

Sciurini Sciurini () is a tribe that includes about forty species of squirrels,Thorington and Hoffmann, 2005, p. 754 mostly from the Americas. It includes five living genera—the American dwarf squirrels, '' Microsciurus''; the Bornean '' Rheithrosc ...

– tree squirrels (5 genera, about 38 species) ** Tribe Pteromyini – true flying squirrels (15 genera, about 45 species) * Subfamily

Callosciurinae The Callosciurinae are an Asiatic subfamily of squirrels containing over 60 species (mostly found in South East Asia) named after the genus '' Callosciurus'', which means "beautiful squirrels". Classification *Family SciuridaeThorington, R. W. ...

– Asian ornate squirrels ** Tribe

Callosciurini Callosciurini is a tribe of tree squirrels mainly found in southern Asia. Species Source: * Genus '' Callosciurus'' **''Callosciurus adamsi'' ( ear-spot squirrel) **''Callosciurus albescens'' ( Kloss's squirrel) **''Callosciurus baluensis'' ( K ...

(13 genera, nearly 60 species) ** Tribe Funambulini palm squirrels (1 genus, 5 species) * Subfamily

Xerinae The Xerinae comprise a subfamily of squirrels, many of which are highly terrestrial. It includes the tribes Marmotini (marmots, chipmunks, prairie dogs, and other Holarctic ground squirrels), Xerini (African and some Eurasian ground squirrels), ...

– terrestrial squirrels ** Tribe

Xerini Xerini is a tribe of ground squirrels occurring in Africa and Asia. With the tribes Marmotini (Holarctic ground squirrels) and Protoxerini (African tree squirrels), they form the subfamily Xerinae. There are five living genera—'' Xerus'', the ...

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

Protoxerini The Protoxerini comprise a tribe of squirrels found in Africa. The 30 species in six genera are:Thorington, R. W. and R. S. Hoffmann. 2005. Family Sciuridae. Pp 754–818 in Mammal Species of the World A Taxonomic and Geographic Reference. Johns ...

(6 genera, about 50 species) ** Tribe Marmotini – ground squirrels, marmots, chipmunks, prairie dogs, etc. (6 genera, about 90 species)

Relationship with humans

References

Sources

*

External links

*
Tree of Life: Sciuridae

How to identify squirrel tracks in the wild

{{Authority control Sciuromorpha Articles containing video clips Extant Eocene first appearances Rodents by common name Taxa named by Gotthelf Fischer von Waldheim

Etymology

Characteristics

Head

Tail

Lifetime

Behavior

Feeding

Taxonomy

Taxonomy list

Relationship with humans

See also

References

Sources

Further reading

External links