This family of 50 living genera and 260 species is found in a wide variety of habitats throughout the world except in the Australian region, Madagascar, southern South America, and certain desert regions, such as in Egypt and the Arabian Peninsula.
Squirrels are conspicuous and are better known by sight to people than are most rodents.
They range in size from the tropical pygmy squirrels, which weigh less than 10 grams, to the marmots, which can weigh as much as 7.5 kg. Ratufa is the largest arboreal genus. Squirrels and their relatives have a small upper premolar, which is shed in some forms about the time they reach maturity. The molariform teeth are rooted, usually low-crowned, and cuspidate. The upper molariform teeth in sciurids usually have four transverse ridges, each with a slight or prominent cusp on the outer border.