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Sciuridae

(Family)

Overview

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The sciurids or are a large family of rodents. The word Sciuridae means "shade-tail," and refers to the bushy appendage possessed by many of its members1]. It includes tree squirrels, ground squirrels, chipmunks, the marmots (which include woodchucks), and the true flying squirrels. The African scaly-tailed flying squirrels, which belong to the family Anomaluridae, are not sciurids. Sciurids are found in all continents except Australia and Antarctica.

Characteristics

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Skull of an Oriental giant squirrel (genus Ratufa). Note the classic sciuromorphous shape of the anterior zygomatic region.

Sciurids are generally small animals, ranging in size from the African Pygmy Squirrel, at 7–10 cm (2.8–3.9 in) in length, and just 10 g (0.35 oz) in weight, to the Alpine Marmot, which is 53–73 cm (21–29 in) long, and weighs from 5 to 8 kg (11 to 18 lb). Sciurids 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 sciurids is highly variable between - and often even within - species.

The hindlimbs of sciurids 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 of sciurids also have a soft pad on the underside.[2]

Sciurids 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. Indeed, some tropical species have shifted almost entirely to a diet of insects. The teeth of sciurids follow the typical rodent pattern, with large gnawing incisors that grow throughout life, and grinding cheek teeth set back behind a wide gap, or diastema. The typical dental formula for sciurids is:

As their large eyes indicate, sciurids generally have an excellent sense of vision, which is especially important for tree-dwelling species. Many also have a good sense of touch, with vibrissae on their heads and limbs.[2]

Sciurids 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, blind, and helpless. In almost all species, only the female looks after the young, which are 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-[2]

Evolution and Systematics

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Grizzled Giant Squirrel (Ratufa macroura) of the Ratufinae
Southern Flying Squirrel (Glaucomys volans) of the Pteromyini
Prevost's Squirrel (Callosciurus prevosti) of the Callosciurini
Unstriped Ground Squirrel (Xerus rutilus) of the Xerini
Alpine Marmot (Marmota marmota) of the Marmotini

The living squirrels are divided into 5 subfamilies, with about 50 genera and nearly 280 species. Though the oldest squirrel fossil, Douglassciurus, dates back to the Priabonian (Late Eocene, around 37.5 - 35 million years ago), this animal was apparently a nearly-modern tree squirrel, albeit with a primitive skull, and it is in fact usually placed in the Sciurinae. Thus, the squirrel lineage may well have originated quite some time earlier.[3]

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 "proto-squirrels" (in the sense that they lacked the full range of living squirrels' autapomorphies). The distribution and diversity of such ancient and ancestral forms suggests that the squirrels as a group might have originated in North America.[3]

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 but were more widespread across Eurasia in prehistoric times. 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 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.[3]

The main group of squirrels also can be split up in three, which yields the remaining subfamilies. The Sciurinae are the only squirrel group for which there is significant uncertainty as regards taxonomy. Namely, it is not altogether clear how distant the true flying squirrels (Pteromyini) are from the tree squirrels (Sciurini); the former have often been considered a separate subfamily but are now seen as a tribe of the Sciurini. The pine squirrels 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.[4]

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 arboricolous (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 arboricolous, but have a markedly different habitus and appear more "elegant", an effect enhanced by their often very colorful fur. The Xerinae - the largest subfamily - are made up from the mainly terrestrial (ground-living) forms and include the large marmots and the popular prairie dogs among others; they tend to be more gregarious than other squirrels which do not usually live together in close-knit groups.[3]

Photos

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Taxonomy

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The Family Sciuridae is further organized into finer groupings including:

Genera

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Aeretes

The Groove-toothed Flying Squirrel or North Chinese Flying Squirrel (Aeretes melanopterus) is a species of in the Sciuridae family. It is monotypic within the genus Aeretes. It is endemic to China. Its natural habitat is temperate forests. [more]

Aeromys

Large black flying squirrels ( Aeromys) form a taxon of squirrels under the tribe Pteromyini. They are only found in South-east Asia. [more]

Aethosciurus

Ammospermophilus

The antelope squirrels or antelope ground squirrels are the genus Ammospermophilus of found in the southwestern United States and northern Mexico. [more]

Arctomyoides

[more]

Arctomys

Atlantoxerus

The Barbary Ground Squirrel (Atlantoxerus getulus) is a species of in the Sciuridae family. It is monotypic within the genus Atlantoxerus. It is found in Algeria, Morocco, Spain, and Western Sahara. Its natural habitats are subtropical or tropical dry shrubland, temperate grassland, and rocky areas. [more]

Belomys

The hairy-footed flying squirrel (Belomys pearsonii) is a found in the mountains of the eastern Himalaya, Southeast Asia, and southern China till the island of Taiwan. It lives at altitudes between 1500 and 2400 m above sea level. [more]

Biswamoyopterus

The Namdapha Flying Squirrel (Biswamoyopterus biswasi), the sole species placed in the genus Biswamoyopterus, is an , nocturnal flying squirrel endemic to India, and is listed as a critically endangered species due to habitat loss. First collected in Deban (on 27 April 1981), no population estimates are available for B. biswasi, but the known habitat is tall Mesua ferrea jungles, often on hill slopes in the catchment area of Noa Dihing river (particularly on the western slope of Patkoi range) [more]

Blackia

[more]

Callosciurus

Callosciurus is a genus of squirrels. Several of the species have settled on small islands, and have developed separate subspecies. In total, the genus contains 14 species and up to 300 subspecies or varieties. The genera Glyphotes, Rubrisciurus, and Tamiops are sometimes also included in Callosciurus. [more]

Callospermophilus

Cedromus

Citellus

[more]

Cynomys

Prairie dogs (Cynomys) are burrowing (not actually dogs) native to the grasslands of North America. There are five different species of prairie dogs: black-tailed, white-tailed, Gunnison, Utah, and Mexican prairie dogs. They are a type of ground squirrel. On average, these stout-bodied rodents will grow to be between 30–40 centimetres (12–16 in) long, including the short tail and weigh between 0.5–1.5 kilograms (1–3 lb). They are found in the United States, Canada, and Mexico. In Mexico, prairie dogs are primarily found in the northern states which are the southern end of the great plains: northeastern Sonora, north and northeastern Chihuahua, northern Coahuila, northern Nuevo León, and northern Tamaulipas; in the U.S., they range primarily west of the Mississippi River, though they have also been introduced in a few eastern locales. They will eat all sorts of vegetables and fruits. [more]

Dremomys

Red-cheeked Squirrels ( Dremomys) form a taxon of squirrels under the subfamily Callosciurinae. They are only found in Asia. [more]

Eoglaucomys

The Kashmir Flying Squirrel (Eoglaucomys fimbriatus) is a species of in the Sciuridae family. It is monotypic within the genus Eoglaucomys. It is found in India and Pakistan. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss. [more]

Epixerus

Epixerus is a genus of in the Sciuridae family, found in Africa. It contains the following species: [more]

Eupetaurus

The Woolly Flying Squirrel (Eupetaurus cinereus) is the sole species placed in the genus Eupetaurus. Until recently scientific knowledge of this rare species was limited to 11 skins collected in the late nineteenth century. However, recent research has confirmed that it is still extant in Kashmir. It is the longest member of the family Sciuridae and the most massive gliding animal known, but observations confirm that despite its size, it does glide effectively like other flying squirrels. [more]

Eutamias

Chipmunks are small -like rodents of the genus Tamias. They are native to North America and Asia. [more]

Euxerus

Exilisciurus

Exilisciurus is a genus of in the Sciuridae family. It contains the following species: [more]

Funambulus

Funambulus is a genus of in the Sciuridae family. It contains the following species: [more]

Funisciurus

African striped squirrels ( Funisciurus), or rope squirrels, form a taxon of squirrels under the subfamily Xerinae and the tribe Protoxerini. They are only found in western and central Africa. [more]

Geosciurus

Glaucomys

The two species of New World flying squirrels, genus Glaucomys, are the only species of found in North America. They are distributed from Alaska to Honduras. They are similar in many ways to the Eurasian flying squirrels in the genus Pteromys. The two species of New World flying squirrels can be easily distinguished on the basis of size and ventral pelage. Northern flying squirrels, Glaucomys sabrinus are larger and have belly hair that is dark at the base and white at the tip. Southern flying squirrels, Glaucomys volans, are smaller and have belly hairs that are completely white. [more]

Glyphotes

The Sculptor Squirrel (Glyphotes simus) is a species of in the Sciuridae family. It is monotypic within the genus Glyphotes. It is endemic to Malaysia. [more]

Guerlinguetus

Heliosciurus

Sun squirrels ( Heliosciurus), form a taxon of squirrels under the subfamily Xerinae and the tribe Protoxerini. They are only found in sub-Saharan Africa. [more]

Heteroxerus

[more]

Hylopetes

Hylopetes is a genus of . [more]

Hylopetus

Hyosciurus

Hyosciurus is a genus of in the Sciuridae family found in Indonesia. It contains the following species: [more]

Iomys

Iomys is a genus of in the Sciuridae family. Its species include: [more]

Lariscus

Striped ground squirrels ( Lariscus) form a taxon of squirrels under the subfamily Callosciurinae. They are only found in South-east Asia. [more]

Marmota

Marmots are members of the Marmota, in the rodent family Sciuridae (squirrels). [more]

Menetes

A Genus in the Kingdom Animalia. [more]

Microsciurus

Microsciurus or dwarf squirrels is a genus of squirrels from the tropical regions of and South America. [more]

Miopetaurista

Miosciurus

Miospermophilus

Myosciurus

The African Pygmy Squirrel (Myosciurus pumilio) is a species of in the Sciuridae family. It is monotypic within the genus Myosciurus. It is found in Cameroon, Republic of the Congo, Equatorial Guinea, and Gabon. Its natural habitat is subtropical or tropical moist lowland forests. It is threatened by habitat loss. [more]

Nannosciurus

The Black-eared Squirrel (Nannosciurus melanotis) is a species of in the Sciuridae family. It is monotypic within the genus Nannosciurus. It is found in Indonesia and Malaysia. [more]

Neosciurus

[more]

Neotamias

Nototamias

[more]

Oligospermophilus

Otospermophilus

[more]

Paenemarmota

Palaeosciurus

Parapaenemarmota

Paratamias

Paraxerus

African bush squirrels ( Paraxerus) form a taxon of squirrels under the subfamily Xerinae. They are only found in Africa. [more]

Petaurillus

Pygmy flying squirrels (Petaurillus) are a genus of . [more]

Petaurista

A Genus in the Kingdom Animalia. [more]

Petauristodon

[more]

Petinomys

Petinomys is a genus of in the Sciuridae family. It contains the following species: [more]

Pliopetaurista

Pliopetes

Prosciurillus

Prosciurillus is a genus of in the Sciuridae family, found in Indonesia. It contains the following species: [more]

Protosciurus

Protospermophilus

Protoxerus

African Giant Squirrels ( Protoxerus) form a taxon of squirrels under the subfamily Sciurinae. They are only found in Africa. [more]

Pteromys

Commonly referred to as simply the Old World flying squirrels, the genus Pteromys is distributed across Eurasia and Japan. Although there are a host of flying squirrel genera in Asia (particularly southern Asia), Pteromys is the only one present in Europe. [more]

Pteromyscus

The Smoky Flying Squirrel (Pteromyscus pulverulentus) is a species of in the Sciuridae family. It is monotypic within the genus Pteromyscus. It is found in Brunei, Indonesia, Malaysia, and Thailand. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss. [more]

Ratufa

Oriental giant squirrels are very large from the genus Ratufa in the subfamily Ratufinae. They are found in parts of south- and southeast Asia. [more]

Rheithrosciurus

The Tufted Ground Squirrel (Rheithrosciurus macrotis) is a species of in the Sciuridae family. It is monotypic within the genus Rheithrosciurus. It is found in Indonesia and Malaysia. [more]

Rhinosciurus

The Shrew-faced Squirrel (Rhinosciurus laticaudatus) is a species of in the Sciuridae family. It is monotypic within the genus Rhinosciurus. It is found in Brunei, Indonesia, Malaysia, Singapore, and possibly Thailand. [more]

Rubrisciurus

The Red-bellied squirrel (Rubrisciurus rubriventer) is a species of . Until recently, it was described as a species in the genus Callosciurus, but since the 1990s it is generally placed in its own genus Rubrisciurus. It is endemic on the Indonesian island of Sulawesi. With a length of 25 cm (head and body), it is rather large for a squirrel. It lives in the tree tops of the rainforests of the island. [more]

Ruficaudus

Rupestes

[more]

Sciurillus

The Neotropical Pygmy Squirrel, Sciurillus pusillus, is a very small species from South America. It is the only living member of the genus Sciurillus and the subfamily Sciurillinae. It is found in the lowland rainforests of Brazil, Colombia, Peru, French Guiana, Guyana and Suriname. [more]

Sciurion

Sciuropterus

[more]

Sciurotamias

Sciurotamias is a genus of in the Sciuridae family, found in China. It contains the following species: [more]

Sciurus

The genus Sciurus contains most of the common, bushy-tailed in North America, Europe, temperate Asia, Central America and South America. [more]

Similisciurus

Spermophilinus

[more]

Spermophilopsis

The Long-clawed Ground Squirrel (Spermophilopsis leptodactylus) is a species of in the Sciuridae family. It is monotypic within the genus Spermophilopsis. It is found in Afghanistan, Iran, Kazakhstan, Tajikistan, Turkmenistan, and Uzbekistan. [more]

Spermophilus

The genus Spermophilus is the largest genus of ground squirrels and the one that contains the species that are most common and familiar in . Members of the genus are found from western Europe to Siberia and Alaska to northern Mexico. The Eurasian species are sometimes called susliks (or sousliks). The latter name come from Russian ??????, suslik (compare also Polish: )[citation needed] [more]

Spermophulis

Sundasciurus

Sundasciurus is a genus of in the Sciuridae family. It contains the following species: [more]

Syntheosciurus

Bangs's Mountain Squirrel (Syntheosciurus brochus) is a nearly unknown species of tree squirrel, that only lives in and Panama. It can be found in mountain rain forests at an altitude between 1900 and 2600 meters, and lives mainly in the tree tops, but sometimes on the forest floor as well. One of its habitats is at the summit of the Poás Volcano in Costa Rica, in a Clusia forest that is almost unaccessible for humans. [more]

Tamias

Chipmunks are small -like rodents of the genus Tamias. They are native to North America and Asia. [more]

Tamiasciurus

Pine squirrels are of the genus Tamiasciurus. Currently only two species are classified in this genus, the American Red Squirrel T. hudsonicus and the Douglas Squirrel T. douglasii. Both are native to North America: pine squirrels can be found in the northern and western United States, most of Canada and Alaska. [more]

Tamiops

Asiatic Striped Squirrels ( Tamiops) form a taxon of squirrels under the subfamily Callosciurinae. They are only found in Asia. [more]

Trogopterus

The complex-toothed flying squirrel (Trogopterus xanthipes) is a found in the southern Chinese provinces Hubei, Hunan, Guizhou, Sichuan and Yunnan. Its name originates from the teeth, which differ from the other flying squirrels. The squirrel looks similar to other flying squirrels, most strikingly is a cluster of black hair at the bottom of the ear. The fur is grey-brown on top and white on bottom. Both its face and its tail are slightly red. The length of the body is about 30 cm, plus the tail which is another 30 cm long. [more]

Xerus

African ground squirrels ( Xerus) form a taxon of squirrels under the subfamily Xerinae. They are only found in Africa and The Canary Islands. [more]

At least 9 species and subspecies belong to the Genus Xerus.

More info about the Genus Xerus may be found here.

References

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Footnotes

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  1. ^ Whitaker & Elman (1980): 370
  2. ^ a b c Milton (1984)
  3. ^ a b c d Steppan & Hamm (2006)
  4. ^ Steppan et al. (2004), Steppan & Hamm (2006)

Sources

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Last Revised: April 26, 2010
2010/04/26 16:03:24