Pachycephalosaurus

Pachycephalosaurus was a dome-headed dinosaur that roamed western North America during the Late Cretaceous. Its most striking feature was an incredibly thick, rounded skull roof, which may have been used for head-butting. This plant-eater grew up to 4.5 meters long and weighed as much as a small car.

• Had a skull roof up to 25 cm (10 inches) thick
• Lived about 70-66 million years ago in Montana and surrounding areas
• Some scientists debate whether Stygimoloch was a separate species or just a young Pachycephalosaurus