Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
   Subclass Ornithurae Haeckel, 1866 see Clade Ornithurae Haeckel 1866 [Gauthier 1986] {Chiappe 1991}
     Infraclass Ratitae (Merrem, 1813) P. Brodkorb, 1963 see Parvclass Ratitae (Merrem, 1813)
       Order Rheiformes Forbes, 1884 see Suborder Rheae Forbes, 1884
         Family Rheidae Bonaparte, 1849 - rheas
           Genus Pterocnemia Gray, 1871