Pachycephalosaurus was a dinosaur that lived in the Late Cretaceous Period in North America. This dinosaur's mass is 2,200 lbs and it was 15 feet long. It is a species of pachycephalosaurid. This dinosaur headbutted its enemies. This dinosaur had low intelligence but a good sense of smell. It had a small brain because its 9-inch thick skull did not let its brain get that big. This dinosaur ate plants with it's beak.