THYREOPHORAORNITHOPODAStenopelixGoyocephaleHomalocephaleStegocerasTylocephalePrenocephaleStygimolochPachycephalosaurusPsittacosaurusChaoyangsaurusArchaeoceratopsLeptoceratopsPROTOCERATOPSIDAEMontanoceratopsTuranoceratopsCENTROSAURINAECERATOPSINAEOsteologyMaximum ParsimonyBased on reanalysis of the original matrix.Sereno_1999ad