Vertebrata Cuvier, 1812 - vertebrates
   Gnathostomata
     Teleostomi
       Tetrapoda Hatschek & Cori 1896 [Gauthier, Kluge & Rowe 1988]
         Amniota Haeckel, 1866 [Gauthier, Kluge & Rowe 1988] - amniotes
           Class Reptilia Linnaeus, 1758 [paraphyletic] - reptiles
             Subclass Diapsida Osborn, 1903 - diapsids see Clade Diapsida Osborn 1903 [Gauthier & de Queiroz 2020]
               Infraclass Lepidosauromorpha Benton, 1983 see Subclass Lepidosauromorpha Benton, 1983
                 Superorder †Sauropterygia Owen, 1860
                   Order †Plesiosauria Blainville, 1835 - plesiosaurs
                     Superfamily †Plesiosauroidea Nopcsa, 1928 see Suborder Plesiosauroidea Welles, 1943
                       1 Family †Plesiosauridae Gray, 1825 [monotypic]
                       2 Family †Cryptoclididae Williston, 1925
                       3 Family †Elasmosauridae Cope, 1869