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
                     1 Superfamily †Plesiosauroidea Nopcsa, 1928 see Suborder Plesiosauroidea Welles, 1943
                     2 Superfamily †Pliosauroidea Welles, 1943 [monotypic] see Suborder Pliosauroidea Welles, 1943
                     3 Genus †Aptychodon Reuss, 1855, incertae sedis
                     4 Genus †Brimosaurus Leidy, 1854, nom. dub., incertae sedis
                     5 Genus †Discosaurus Leidy, 1851, incertae sedis
                     6 Genus †Piptomerus Cope, 1887, incertae sedis
                     7 Genus †Piratosaurus Leidy, 1865, incertae sedis
                     8 Genus †Sthenarosaurus Watson, 1909, incertae sedis