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Sunday, November 1, 2020

Squirrel

Etymology

The word squirrel, first attested in 1327, comes via Anglo-Norman esquirel from the Old French escurel, the reflex of a Latin word sciurus which was itself borrowed from Greek. The word itself comes from the Greek word , skiouros, which means shadow-tailed, referring to the bushy appendage possessed by many of its members.

The native Old English word, ‘cweorna', survived only into Middle English (as aquerna) before being replaced. The Old English word is of Common Germanic origin, with cognates such as German Eichhorn/Eichhrnchen and Norwegian ekorn.

Characteristics

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, at 710 cm (2.83.9 in) in length, and just 10 g (0.35 oz) in weight, to the Alpine marmot, which is 5373 cm (2129 in) long, and weighs from 5 to 8 kg (11 to 18 lb). 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 and often even within species.

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.

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. 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:

Dentition

1.0.1.3

1.0.1.3

As their large eyes indicate, squirrels generally have an excellent sense of vision, which is especially important for tree-dwelling species. They also have very versatile and sturdy claws for grasping and climbing. Many also have a good sense of touch, with vibrissae on their heads and limbs.

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, 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-

Ground and tree squirrels are typically diurnal, while flying squirrels tend to be nocturnalxcept for lactating flying squirrels and their offspring, which have a period of diurnality during the summer.

Diet

Unlike rabbits or deer, squirrels cannot digest 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, since 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 nuts, seeds, conifer cones, fruits, fungi and green vegetation. However some squirrels also consume meat, especially when faced with hunger. Squirrels have been known to eat insects, eggs, small birds, young snakes and smaller rodents.

Predatory behavior by various species of ground squirrels, particularly the thirteen-lined ground squirrel, has been noted. Bailey, for example, observed a thirteen-lined ground squirrel preying upon a young chicken. Wistrand reported seeing this same species eating a freshly killed snake. 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; Bradley, examining white-tailed antelope squirrels' stomachs, found at least 10% of his 609 specimens' stomachs contained some type of vertebrateostly lizards and rodents. Morgart (1985) observed a white-tailed antelope squirrel capturing and eating a silky pocket mouse.

Evolution and systematics

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. 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.

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.

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 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.

The main group of squirrels also can be split up in three, which yields the remaining subfamilies. The Sciurinae contains the flying squirrels (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 of the Sciurinae. The pine squirrels (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.

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 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, 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.

Basal and incertae sedis Sciuridae (all fossil)

Getuloxerus

Hesperopetes

Kherem

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

^ a b “Squirrel”. Online Etymology Dictionary. http://www.etymonline.com/index.php?term=squirrel. Retrieved 2008-02-07. 

^ Whitaker & Elman (1980): 370

^ a b c Milton (1984)

^ “Squirrel” – HowStuffWorks

^ Trml, Timo; Vuorinen, Hannu; Hokkanen, Heikki (1980). “Timing of circadian activity in the flying squirrel in central Finland”. Acta Theriologica 25 (3242): 461474. http://acta.zbs.bialowieza.pl/contents/?art=1980-025-32-42-0461. Retrieved 2007-07-11. 

^ “Tree Squirrels”. The Humane Society of the United States. http://www.hsus.org/wildlife/a_closer_look_at_wildlife/tree_squirrels.html. Retrieved 2009-01-09. 

^ Friggens, M. (2002). “Carnivory on Desert Cottontails by Texas Antelope Ground Squirrels”. The Southwestern Naturalist 47 (1): 132133. doi:10.2307/3672818. 

^ Bailey, B. (1923). “Meat-eating propensities of some rodents of Minnesota”. Journal of Mammalogy 4: 129. 

^ Wistrand, E.H. (1972). “Predation on a Snake by Spermophilus tridecemlineatus”. American Midland Naturalist 88 (2): 511512. doi:10.2307/2424389. 

^ Whitaker, J.O. (1972). “Food and external parasites of Spermophilus tridecemlineatus in Vigo County, Indiana”. Journal of Mammalogy 53 (3): 644648. doi:10.2307/1379067. 

^ Bradley, W. G. (1968). “Food habits of the antelope ground squirrel in southern Nevada”. Journal Of Mammalogy 49 (1): 1421. doi:10.2307/1377723. 

^ Morgart, J.R. (May 1985). “Carnivorous behavior by a white-tailed antelope ground squirrel Ammospermophilus leucurus”. The Southwestern Naturalist 30 (2): 304305. doi:10.2307/3670745. 

^ Emry, R.J. and Korth, W.W. 2007. A new genus of squirrel (Rodentia, Sciuridae) from the mid-Cenozoic of North America. Journal of Vertebrate Paleontology 27(3):693698.

^ a b c Steppan & Hamm (2006)

^ Steppan et al. (2004), Steppan & Hamm (2006)

Literature cited

Milton, Katherine (1984): [Family Sciuridae]. In: Macdonald, D. (ed.): The Encyclopedia of Mammals: 612623. Facts on File, New York. ISBN 0-87196-871-1

Steppan, Scott J. & Hamm, Shawn M. (2006): Tree of Life Web Project Sciuridae (Squirrels). Version of 2006-MAY-13. Retrieved 2007-DEC-10.

Steppan, Scott 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” (pdf). Mol. Phyl. Evol. 30(3): 703719. 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: 754818. 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

Wikimedia Commons has media related to: Sciuridae

Wikispecies has information related to: Sciuridae

Tree of Life: Sciuridae

Squirrel Tracks: How to identify squirrel tracks in the wild

National Geographic link on Squirrels

Andrew's Squirrel Encyclopaedia

List of names of squirrel taxa

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Rodent families

Sciuromorpha

llomyidae  Aplodontiidae  ylagaulidae  eithroparamyidae  Sciuridae  Gliridae

Castorimorpha

utypomyidae  Castoridae  hizospalacidae  omyidae  lorentiamyidae  eliscomyidae  Heteromyidae  Geomyidae

Myomorpha

rmintomyidae  Dipodidae  nomalomyidae  imimyidae  Platacanthomyidae  Spalacidae  Calomyscidae  Nesomyidae  Cricetidae  Muridae

Anomaluromorpha

Anomaluridae  arapedetidae  Pedetidae

Hystricomorpha

amquammyidae  obiomyidae  Ctenodactylidae  Diatomyidae  uomyidae  hapattimyidae  saganomyidae  “Baluchimyinae”  athyergoididae  Bathyergidae  Hystricidae  yophiomyidae  iamantomyidae  hiomyidae  enyamyidae  Petromuridae  Thryonomyidae  Erethizontidae  Chinchillidae  Dinomyidae  ephalomyidae  Caviidae  Dasyproctidae  ocardiidae  Cuniculidae  Ctenomyidae  Octodontidae  eoepiblemidae  Abrocomidae  Echimyidae  Myocastoridae  Capromyidae  eptaxodontidae

Prehistoric rodents

(incertae sedis)

urymylidae  lagomyidae  rchetypomyidae  ocomyidae  vanantoniidae  aredomyidae  schyromyidae  heridomyidae  rotoptychidae  egdoumyidae  ciuravidae  ylindrodontidae  elomyidae

indicates extinct taxa

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Extant species of family Sciuridae (subfamilies Ratufinae and Sciurillinae)

Kingdom: Animalia  Phylum: Chordata  Class: Mammalia  Order: Rodentia  Suborder: Sciuromorpha

Ratufinae

(Oriental giant squirrels)

Ratufa

Cream-coloured Giant Squirrel (Ratufa affinis)  Black Giant Squirrel (Ratufa bicolor)  Indian giant squirrel (Ratufa indica)  Grizzled Giant Squirrel (Ratufa macroura)

Sciurillinae

Sciurillus

Neotropical Pygmy Squirrel (Sciurillus pusillus)

Category

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Extant species of family Sciuridae (subfamily Callosciurinae)

Kingdom: Animalia  Phylum: Chordata  Class: Mammalia  Order: Rodentia  Suborder: Sciuromorpha

Callosciurus

Ear-spot Squirrel (Callosciurus adamsi)  Kloss Squirrel (Callosciurus albescens)  Kinabalu Squirrel (Callosciurus baluensis)  Gray-bellied Squirrel (Callosciurus caniceps)  Pallas's Squirrel (Callosciurus erythraeus)  Finlayson's Squirrel (Callosciurus finlaysonii)  Inornate Squirrel (Callosciurus inornatus)  Mentawai Squirrel (Callosciurus melanogaster)  Black-striped Squirrel (Callosciurus nigrovittatus)  Plantain Squirrel (Callosciurus notatus)  Borneo Black-banded Squirrel (Callosciurus orestes)  Phayre's Squirrel (Callosciurus phayrei)  Prevost's Squirrel (Callosciurus prevostii)  Irrawaddy Squirrel (Callosciurus pygerythrus)  Anderson's Squirrel (Callosciurus quinquestriatus)

Dremomys

(Red-cheeked squirrels)

Bornean Mountain Ground Squirrel (Dremomys everetti)  Red-throated Squirrel (Dremomys gularis)  Orange-bellied Himalayan Squirrel (Dremomys lokriah)  Perny's Long-nosed Squirrel (Dremomys pernyi)  Red-hipped Squirrel (Dremomys pyrrhomerus)  Asian Red-cheeked Squirrel (Dremomys rufigenis)

Exilisciurus

Philippine Pygmy Squirrel (Exilisciurus concinnus)  Least Pygmy Squirrel (Exilisciurus exilis)  Tufted Pygmy Squirrel (Exilisciurus whiteheadi)

Glyphotes

Sculptor Squirrel (Glyphotes simus)

Hyosciurus

Montane Long-nosed Squirrel (Hyosciurus heinrichi)  Lowland Long-nosed Squirrel (Hyosciurus ileile)

Lariscus

(Striped ground squirrels)

Four-striped Ground Squirrel (Lariscus hosei)  Three-striped Ground Squirrel (Lariscus insignis)  Niobe Ground Squirrel (Lariscus niobe)  Mentawai Three-striped Squirrel (Lariscus obscurus)

Menetes

Berdmore's Ground Squirrel (Menetes berdmorei)

Nannosciurus

Black-eared Squirrel (Nannosciurus melanotis)

Prosciurillus

Secretive Dwarf Squirrel (Prosciurillus abstrusus)  Whitish Dwarf Squirrel (Prosciurillus leucomus)  Celebes Dwarf Squirrel (Prosciurillus murinus)  Sanghir Squirrel (Prosciurillus rosenbergii)  Weber's Dwarf Squirrel (Prosciurillus weberi)

Rhinosciurus

Shrew-faced Squirrel (Rhinosciurus laticaudatus)

Rubrisciurus

Red-bellied squirrel (Rubrisciurus rubriventer)

Sundasciurus

Subgenus Aletesciurus: Davao Squirrel (Sundasciurus davensis)  Horse-tailed Squirrel (Sundasciurus hippurus)  Northern Palawan Tree Squirrel (Sundasciurus juvencus)  Mindanao Squirrel (Sundasciurus mindanensis)  Culion Tree Squirrel (Sundasciurus moellendorffi)  Philippine Tree Squirrel (Sundasciurus philippinensis)  Palawan Montane Squirrel (Sundasciurus rabori)  Samar Squirrel (Sundasciurus samarensis)  Southern Palawan Tree Squirrel (Sundasciurus steerii)

Subgenus Sundasciurus: Brooke's Squirrel (Sundasciurus brookei)  Fraternal Squirrel (Sundasciurus fraterculus)  Jentink's Squirrel (Sundasciurus jentinki)  Low's Squirrel (Sundasciurus lowii)  Slender Squirrel (Sundasciurus tenuis)

Tamiops

(Asiatic striped squirrels)

Himalayan Striped Squirrel (Tamiops mcclellandii)  Maritime Striped Squirrel (Tamiops maritimus)  Cambodian Striped Squirrel (Tamiops rodolphii)  Swinhoe's Striped Squirrel (Tamiops swinhoei)

Funambulus

Subgenus Funambulus: Layard's Palm Squirrel (Funambulus layardi)  Indian Palm Squirrel (Funambulus palmarum)  Dusky Palm Squirrel (Funambulus sublineatus)  Jungle Palm Squirrel (Funambulus tristriatus)

Subgenus Prasadsciurus: Northern Palm Squirrel (Funambulus pennantii)

Category

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Extant species of family Sciuridae (subfamily Sciurinae, Sciurini (Tree squirrels) tribe)

Kingdom: Animalia  Phylum: Chordata  Class: Mammalia  Order: Rodentia  Suborder: Sciuromorpha

Microsciurus

(Dwarf squirrels)

Central American Dwarf Squirrel (Microsciurus alfari)  Western Dwarf Squirrel (Microsciurus mimulus)  Amazon Dwarf Squirrel (Microsciurus flaviventer)  Santander Dwarf Squirrel (Microsciurus santanderensis)

Rheithrosciurus

Tufted Ground Squirrel (Rheithrosciurus macrotis)

Sciurus

Subgenus Tenes: Caucasian Squirrel (Sciurus anomalus)

Subgenus Sciurus: Red Squirrel (Sciurus vulgaris)  Japanese Squirrel (Sciurus lis)  Eastern Gray Squirrel (Sciurus carolinensis)  Mexican Gray Squirrel (Sciurus au

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