The Pachycephalosaurus (pronounced PACKY-sef-elo-soar-us) lived in the Cretaceous Period. It lived in what is now South Dakota, Colorado, and Montana.
The Pachycephalosaurus is known for it's "bump" (AKA a dome-like skull) on it's head that's very hard. Scientist think it was used to fight for territory and to fight over mates. Though it had a big head, it had a small brain.
30 Pachycephalosaurus specimens have been found. It grew to be 16 feet long and 6 feet tall. Pachycephalosaurus skull's have been found to be many different sizes.
That is most of the information that we know about Pachycephalosaurus, thanks for visiting TDT! :D