Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels:
– ground squirrels, amongst which chipmunks and marmots (including woodchucks)
– flying squirrels
– prairie dogs
Squirrels are indigenous to the Americas, Eurasia, and Africa and were introduced by humans to Australia.
More information on Squirrel can be found on Wikipedia.