Class Mammalia Linnaeus, 1758 - mammals
   Subclass Theria Parker & Haswell, 1897
     Order Perissodactyla Owen, 1848 - odd-toed ungulates
       Family Equidae Gray, 1821 [monotypic] - horses, zebras, and asses
         Genus Equus Linnaeus, 1758 - horses, zebras, and asses
           Equus caballus group Linnaeus, 1758 [monotypic]
             Equus caballus Linnaeus, 1758 - horse
               1 [Equus caballus caballus] Linnaeus, 1758
               2 Equus caballus ferus Boddaert, 1785 - tarpan
               3 Equus caballus przewalskii Poliakov, 1881 - Przewalski's horse