Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
   Subclass †Odontoholcae (Marsh, 1875) Stejneger, 1885 see Cohort Ornithurae Haeckel, 1866
     Order †Hesperornithiformes Fürbringer, 1888
       Family †Hesperornithidae Marsh, 1872
         Genus †Hesperornis Marsh, 1872
           1 †Hesperornis regalis Marsh, 1872
           2 †Hesperornis crassipes (Marsh, 1876)
           3 †Hesperornis gracilis Marsh, 1876