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
                       Family †Elasmosauridae Cope, 1869
                         01 Genus †Alzadasaurus Welles, 1943
                         02 Genus †Aphrosaurus Welles, 1943
                         03 Genus †Brancasaurus Wegner, 1914
                         04 Genus †Elasmosaurus Cope, 1868
                         05 Genus †Fresnosaurus Welles, 1943
                         06 Genus †Hydralmosaurus Welles, 1943
                         07 Genus †Hydrotherosaurus Welles, 1943
                         08 Genus †Leurospondylus Brown, 1914
                         09 Genus †Mauisaurus Hector, 1874
                         10 Genus †Microcleidus Watson, 1909
                         11 Genus †Muraenosaurus Seeley, 1874
                         12 Genus †Morenosaurus Welles, 1943
                         13 Genus †Styxosaurus Welles, 1943
                         14 Genus †Thalassomedon Welles, 1943
                         15 Genus †Tricleidus Andrews, 1909
                         16 Genus †Woolungasaurus Persson, 1960, nom. dub.