Pachycephalosaurus

Pachycephalosaurus was a medium-sized herbivorous dinosaur that lived in the late Cretaceous period, 89 to 75 million years ago, in North America. They are famous as "bone-head" dinosaurs, due to the 9-inch thick rounded plate of bone in their foreheads. Contrary to popular belief, Pachycephalosaurus did not butt heads with each other.

In Jurassic Park
Pachycephalosaurus may be seen in The Lost World: Jurassic Park, ramming into hunters and equipment. They were, however, only half the size of real Pachycephalosaurs.

In Operation Genesis
Pachycephalosaurus may also be seen in the game Jurassic Park: Operation Genesis as a three-star small herbivore, at closer to its correct length than those of the movie.