Order †Ornithischia Seeley, 1887
   Parvorder †Genasauria Sereno, 1986 see Clade Genasauria Sereno 1986
     Nanorder †Cerapoda Sereno, 1986 see Suborder Cerapoda Sereno, 1986
       Hypoorder †Marginocephalia Sereno, 1986 see Clade Marginocephalia Sereno 1986
         Suborder †Pachycephalosauria Maryañska & Osmólska, 1974 see Infraorder Pachycephalosauria Maryañska & Osmólska, 1974
           Infraorder †Goyocephalia Sereno, 1986 see Infraorder Pachycephalosauria Maryañska & Osmólska, 1974
             Superfamily †Homalocephaloidea Dong, 1978 see Infraorder Pachycephalosauria Maryañska & Osmólska, 1974
               Family †Tholocephalidae Sereno, 1986, nom. inval. see Family Pachycephalosauridae Sternberg, 1945
                 Subfamily †Domocephalinae Sereno, 1986, nom. inval. see Family Pachycephalosauridae Sternberg, 1945
                   Genus †Pachycephalosaurus Brown & Schlaikjer, 1943