Phylum [Vertebrata] (Lamarck, 1801)
   Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
     Subclass †Odontornithes (Marsh, 1873)
       Order †Hesperornithiformes Fürbringer, 1888
         Genus †Hesperornis Marsh, 1872