Order †Pachycephalosauria Maryañska & Osmólska, 1974 see Infraorder Pachycephalosauria Maryañska & Osmólska, 1974
   Family †Pachycephalosauridae Sternberg, 1945
     †Pachycephalosaurini Sullivan, 2003
       Genus †Tylosteus Leidy, 1872, nom. oblit. see Genus Dracorex Bakker, R. Sullivan, Porter, P. Larson & Saulsbury, 2006
         †Tylosteus ornatus Leidy, 1872, nom. oblit. see Dracorex hogwartsia Bakker, Sullivan, Porter, Larson & Saulsbury, 2006