Clade Lepidosauria Haeckel 1866 [de Queiroz & Gauthier 2020] see Subclass Lepidosauria Duméril & Bibron, 1839
   Clade Rhynchocephalia Günther 1867 [Gauthier, Estes & de Queiroz 1988] see Order Rhynchocephalia Günther, 1867
     Clade Sphenodontia Williston 1925 [Evans 2003]
       Clade Acrosphenodontia Chambi-Trowell, Martinelli, Whiteside, Romo de Vivar, Soares, Schultz, Gill, Benton & Rayfield 2021
         Clade Eusphenodontia Herrera-Flores, Stubbs, Elsler & Benton 2018
           1 Genus †Polysphenodon Jaekel, 1911
           2.1 Genus †Opisthiamimus DeMar, Jones & Carrano, 2022 [monotypic]
           2.2.1 Clade †Clevosauridae Fraser 1993 [Bonaparte & Sues 2006] see Family Clevosauridae Fraser, 1993
           2.2.2 Clade Neosphenodontia Herrera-Flores, Stubbs, Elsler & Benton 2018