Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
   Pygostylia Chatterjee 1997 [Chiappe 2001]
     Ornithothoraces Chiappe 1995
       1 †Enantiornithes Walker 1981 [Sereno 1998] see Infraclass Enantiornithes Walker, 1981
       2 Subclass Ornithuromorpha Chiappe, 2002 see Clade Ornithuromorpha Chiappe 2001