A rooted dinosaur tooth of an indeterminate pachycephalosaurid from the Hell Creek Formation in Carter County, Montana, United States. There are many species of pachycephalosaurids found during the Maastrichtian of North America such as, Pachycephalosaurus wyomingensis, Platytholus clemensi, Sphaerotholus buchholtzae, Sphaerotholus triregnum and the controversial Stygimoloch spinifer and Dracorex hogwartsia. Stygimoloch has more recently been identified as a valid species, but it's unclear if it is distinct enough to be its own genus. Dracorex, while not extensively studied, may lean towards Stygimoloch. Size wise, it could lean towards Pachycephalosaurus and Stygimoloch (Dracorex) over the two smaller pachycephalosaurid genera. Regardless of the validity of some proposed species, pachycephalosaurids were remained very diverse to the very end of the Mesozoic. The prominent raised ridged down the center of the crown distinguishes pachycephalosaurids from the similarly toothed contemporary basal ornithischian, Thescelosaurus. Unlike Thescelosaurus, pachycephalosaurid teeth can also be quite unsymmetrical.
