For the characteristics of the family Sciuridae and the different squirrel-like genera by which it is represented, see Rodentia.
Beavers are nearly allied to the squirrels (Sciuridae), agreeing in certain structural peculiarities of the lower jaw and skull.
In the Sciuridae the two main bones (tibia and fibula) of the lower half of the leg are quite separate, the tail is round and hairy, and the habits are arboreal and terrestrial.
The Nannosciurinae, or second sub-family of Sciuridae, are represented only by the pigmy squirrels (Nannosciurus), characterized by their very short-crowned molars (which approximate to those of dormice in structure) and small premolars, of which the first upper pair is often deciduous, while the upper molars have only three oblique ridges.
Possibly they are akin to the Sciuridae.