The mountain type of this, seen here, is the most primitive living rodent
It 
loves to eat the stuff that grows well here: sword and bracken ferns,... [DOC] [TLE] Point Arena Mountain Beaver Species Profile [PAR] Apr 11, 2011 ... Official Status: ENDANGERED, the Point Arena mountain beaver is federally ... 
the family Aplodontidae, and are considered the most primitive living rodents.