[Avialae] Gauthier 1986
   Aves Linnaeus 1758 [Gauthier 1986], nom. cl. inval. see Subclass Aves Linnaeus, 1758
     Pygostylia Chatterjee 1997 [Chiappe 2001]
       Ornithothoraces Chiappe 1995
         Ornithuromorpha Chiappe 2001
           Ornithurae Haeckel 1866 [Gauthier 1986] {Chiappe 1991}
             1 Genus †Hesperornis Marsh, 1872
             2.1 Genus †Ambiortus Kurochkin, 1982
             2.2.1 Genus †Ichthyornis Marsh, 1872
             2.2.2 Genus Anas Linnaeus, 1758 - Pacific black duck