Phyllotis

Phyllotis is a genus of rodent in the family Cricetidae. These mice are commonly confused with Auliscomys, Graomys and Loxodontomys. In order to tell these genera apart, one must look at the tail. Species in the genus Phyllotis have a penicillate tip on their tail which is not present in the other two genera. Tails in the genus Phyllotis are also less than the length of its head and body combined whereas in Graomys, tails are longer than the head and body combined. P. xanthopygus was found at the summit of Volcán Llullaillaco (6,739 m), which is the highest altitude a mammal has yet been found