Paenemarmota
Paenemarmota is an extinct genus of ground squirrel from North America. Fossils are known from the Blancan and Hemphillian age from localities in Nebraska, Kansas, Texas, Arizona, and Mexico. At around the size of a beaver, "Paenemarmota" is the largest known member of the squirrel family. Description. "Paenemarmota" is the largest known ground squirrel and is nearly twice as large as the largest living marmots. Weight estimates for "P. barbouri" are around on the basis of femur dimensions, or up to kg on the basis of lengths of premolars. On the basis of lengths of premolars, "P. mexicana" may  have weighed up to , while "P. sawrockensis" was smaller, at up to . Although some of its features are primitive, in general morphology it resembles the ground squirrels of the genus "Spermophilus". The large upper and lower fourth premolars are proportionally very large, a feature shared with modern marmots. The large fourth premolars are exceptions to the general evolutionary trend in the ground squirrels and only in "Paenemarmota" and the living "Marmota" are these teeth larger than the first molars.