Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
   Pygostylia Chatterjee 1997 [Chiappe 2001]
     Ornithothoraces Chiappe 1995
       Subclass Ornithuromorpha Chiappe, 2002 see Clade Ornithuromorpha Chiappe 2001
         Ornithurae Haeckel 1866 [Gauthier 1986] {Chiappe 1991}
           1 Genus †Hesperornis Marsh, 1872
           2.1 Genus †Ichthyornis Marsh, 1872
           2.2 Neornithes Gadow, 1893 - living birds