The skulls of rodents vary in length from .25 inch to over 10 inches long. The tooth count does not exceed 22 except in the Mole Rat which has 28 teeth.
All rodents have incisors that grow continuously throughout their lives.
The family Sciuridae is comprised of 260 species that are found throughout most of the world. They live on a diet of nuts and other plant matter, as well as some small animals and insects. Most inhabit trees and are diurnal however some are most active at night. The order Rodentia consists of small to medium sized mammals which share the common characteristic of a single pair of upper and lower incisors that are specialized for gnawing. Rodentia is the largest order of living mammals, containing approximately 1500 species.