The pachycephalosaurids were close relatives of the ceratopsids and other ceratopsians within the Marginocephalia. They are famous for their thick, domed skulls, which may have been used for flank-pushing competitions (and not the popularly-portrayed head-smashing contests). Some scientists consider this group to include the same creatures as the larger Pachycephalosauria, claiming that the flat-headed members of this group (sometimes separated) represent juveniles of the pachycephalosaurids. The teeth of Stegoceras are almost identical to those of Troodon, suggesting it and the pachycephalosaurs had similar diets, though whether the pachycephalosaurs or Troodon was the omnivore isn't know with certainty (though the latter is a good possibility).
The only members of this group that appear in Dinosaur King are either Secret or Normal Move Card Dinosaurs, so they don't appear to have a "native" element; however, a Dino Holder game website features them as Lightning Dinosaurs.
- Colepiocephale lambei (formerly species of Stegoceras)
- Dracorex hogwartsia (possible juvenile Stygimoloch and/or Pachycephalosaurus)
- Sphaerotholus/S. goodwini/S. buchholtzae
- Stegoceras/S. validum/S. novomexicanum
- Stygimoloch spinifer (possible juvenile Pachycephalosaurus)