* Other squirrels: Gray squirrels, fox squirrels, flying squirrels, ground squirrels, chipmunks, marmots, and prairie dogs.
* Tree squirrels: These are the most closely related to red squirrels, including American red squirrels and Eurasian red squirrels.
Within the Sciuridae family, red squirrels are classified in the Sciurini tribe, which also includes ground squirrels and chipmunks.
Therefore, red squirrels are most closely related to other squirrels, particularly tree squirrels, ground squirrels, and chipmunks.