Serpentes see Suborder Serpentes Linnaeus, 1758
   Alethinophidia Nopcsa, 1923 see Infraorder Alethinophidia Nopcsa, 1923
     Caenophidia Hoffstetter, 1939
       Colubroidea Oppel, 1811
         Family Viperidae Oppel, 1811 - vipers and pit vipers
           1 Subfamily Viperinae Oppel, 1811 - pitless vipers
           2.1 Subfamily Azemiopinae [monotypic]
           2.2 Subfamily Crotalinae Oppel, 1811 - pit vipers