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Tree squirrels are the members of the squirrel family (Sciuridae) most commonly referred to as "squirrels". They include over a hundred primarily tree-dwelling species, native to all continents except Antarctica and Australia.〔 They do not form a single natural, or monophyletic, group, but instead are related to the various other animals in the squirrel family, including ground squirrels, flying squirrels, marmots, and chipmunks. The defining characteristic that is used to determine which of the various species of Sciuridae are tree squirrels is therefore not so dependent on their physiology, but their habitat. Tree squirrels live mostly among trees, as opposed to other squirrels that live in burrows in the ground or among rocks. However, there is one exception to this rule, as physiological distinction does make a difference in regard to flying squirrels, who also make their home in trees, but have unique physical characteristics that separate them from their tree squirrel cousins (specifically, special flaps of skin that act as glider wings, allowing them to "fly"). The most well known genus of tree squirrels is ''Sciurus'', which includes the Eastern gray squirrel of North America (and which was introduced in 1876 to Great Britain〔(【引用サイトリンク】title=How did the grey squirrel arrive in the UK )〕), the red squirrel of Eurasia, and the North American fox squirrel, among many others. Since many tree squirrel species have readily adapted to human-altered environments (including intensely cultivated farms and urban cities), and because they are mostly diurnal (active during the daytime), when most people are outdoors to see them, they are perhaps the most familiar members of the rodent family to most humans. In some larger cities, they are often the only wild mammals that most people ever see. ==Classification== Guy G. Musser, one of the world's leading experts on rodents, and the Archbold Curator Emeritus of Mammalogy at the American Museum of Natural History in New York City, clarifies the usage of "squirrel" and related terms: "The squirrel family includes ground squirrels, chipmunks, marmots, prairie dogs, and flying squirrels, but to most people squirrel refers to the 122 species of tree squirrels, which belong to 22 genera of the subfamily Sciurinae." Current taxonomy, based on genetic data, splits the tree squirrels into several subfamilies. The following genera of the squirrel family are classified as tree squirrels.〔 *Subfamily Ratufinae * *Genus ''Ratufa'' (Asian giant squirrels) *Subfamily Sciurillinae * *Genus ''Sciurillus'' (South American pygmy squirrel) *Subfamily Sciurinae * *Tribe Sciurini (mostly American tree squirrels) * * *Genus ''Microsciurus'' (American dwarf squirrels) * * *Genus ''Rheithrosciurus'' (Borneo tufted ground squirrel) * * *Genus ''Sciurus'' (American and Eurasian tree squirrels) * * *Genus ''Syntheosciurus'' (Central American mountain squirrel) * * *Genus ''Tamiasciurus'' (American red squirrels) *Subfamily Callosciurinae (Asian tree squirrels) * *Genus ''Callosciurus'' (Oriental tree squirrels, introduced into Europe and South America) * *Genus ''Exilisciurus'' (Asian pygmy squirrels) * *Genus ''Funambulus'' (Asian palm squirrels, introduced into Australia in the 1920s)〔〔 * *Genus ''Glyphotes'' (sculptor squirrel) * *Genus ''Nannosciurus'' (Asian dwarf squirrel) * *Genus ''Prosciurillus'' (Sulawesi dwarf squirrels) * *Genus ''Rubrisciurus'' (Sulawesi giant squirrel) * *Genus ''Sundasciurus'' (Sunda squirrels) * *Genus ''Tamiops'' (Asian striped squirrels) *Subfamily Xerinae * *Tribe Protoxerini (African tree squirrels) * * *Genus ''Epixerus'' (African palm squirrels) * * *Genus ''Funisciurus'' (rope squirrels) * * *Genus ''Heliosciurus'' (sun squirrels) * * *Genus ''Myosciurus'' (African pygmy squirrel) * * *Genus ''Paraxerus'' (bush squirrels) * * *Genus ''Protoxerus'' (African giant squirrels) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tree squirrel」の詳細全文を読む スポンサード リンク
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