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} Genus †Hesperornis Marsh, 1872