Vertebrata Cuvier, 1812 - vertebrates
   Gnathostomata
     Teleostomi
       Tetrapoda Hatschek & Cori 1896 [Gauthier, Kluge & Rowe 1988]
         Amniota Haeckel, 1866 [Gauthier, Kluge & Rowe 1988] - amniotes
           Class Mammalia Linnaeus, 1758 - mammals
             Subclass Prototheria Gill, 1872 - monotremes
               Order Monotremata Bonaparte, 1837 - monotremes
                 Family Ornithorhynchidae Gray, 1825 - platypuses