Dinosauria Owen 1841 [Padian & May 1993], nom. cl. inval. see Clade Dinosauria Owen 1842 [Langer, Novas, Bittencourt, Ezcurra & Gauthier 2020] Count: - †Ornithischia Seeley 1887 [Padian & May 1993] see Order Ornithischia Seeley, 1887 Count: - †Genasauria Sereno 1986 Count: - †Neornithischia Cooper 1985 Count: - †Marginocephalia Sereno 1986 Count: - 1 †Pachycephalosauria Maryañska & Osmólska 1974 see Infraorder Pachycephalosauria Maryañska & Osmólska, 1974 Count: - 2 †Ceratopsia Marsh 1890 see Infraorder Ceratopsia Marsh, 1890 Count: -