It had the tallest dome of any known pachycephalosaur. This was the first report of a pachycephalosaur in the Southern Hemisphere. "Pachycephalosaurus" is the largest-known pachycephalosaur. "Majungatholus" was redescribed as an abelisaurid rather than a pachycephalosaur in 1998. An undescribed Pachycephalosaur is present in North Dakota. "Sphaerotholus" is considered a highly derived pachycephalosaur. In 2006, Robert Sullivan published a re-evaluation of pachycephalosaur taxonomy. The upper assemblage also has a tyrannosaurid, a ceratopsian, and a pachycephalosaur. The pachycephalosaur "Hanssuesia" is named for him. Adittionally, it bore a small dome in its head, like a pachycephalosaur. Some burnetiids have a thick domed skull reminiscent of dinocephalians and pachycephalosaur dinosaurs. The tibia shows a pachycephalosaur design, and no tarsal bones appear to be articulated. Other notable early finds include the well-known pachycephalosaur "Stegoceras validum".