Squamata Oppel 1811 [Gauthier, Estes & de Queiroz 1988], nom. cl. inval. see Order Squamata Oppel, 1811
   Episquamata Vidal & Hedges, 2005
     Toxicofera Vidal & Hedges, 2005
       Serpentes see Suborder Serpentes Linnaeus, 1758
         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