Phylum [Vertebrata] (Lamarck, 1801)
   Class Reptilia Linnaeus, 1758 - reptiles
     Subclass †uncertain
       Order †Plesiosauria Blainville, 1835 - plesiosaurs
         1 Family †Plesiosauridae Gray, 1825
         2 Family †Cryptocleididae see Family Cryptoclididae Williston, 1925
         3 Family †Elasmosauridae Cope, 1869
         4 Family †Pliosauridae Seeley, 1874