[Avialae] Gauthier 1986
   Aves Linnaeus 1758 [Gauthier 1986], nom. cl. inval. 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 Ornithuromorpha Chiappe 2001