The mountain type of this, seen here, is the most primitive living rodent
The mountain beaver is the only living rodent with this primitive 
cranial and... [DOC] [TLE] Mountain Beavers - Living with Wildlife | Washington Department of ... [PAR] For more information on the Living With Wildlife series, contact the WDFW 
Wildlife ... by many taxonomists to be the world's most primitive living rodent 
species.