Class Mammalia Linnaeus, 1758 - mammals
   Order Rodentia Bowdich, 1821 - rodents
     Suborder Sciurognathi (Tullberg, 1899) see Suborder Sciuromorpha Brandt, 1855
       Family Sciuridae Batsch, 1788 - squirrels, chipmunks, marmots, and prairie dogs
         Subfamily Sciurinae Batsch, 1788 - tree and ground squirrels
           Genus Microsciurus Allen, 1895 - American pygmy squirrels
             1 Microsciurus alfari (J.A. Allen, 1895) - Alfaro's pygmy squirrel
             2 Microsciurus flaviventer Gray, 1867
             3 Microsciurus mimulus Thomas, 1898 - cloud-forest pygmy squirrel
             4 Microsciurus santanderensis Hernandez-Camacho, 1957