Pachycephalosaurus

dinosaur · thick skull · Late Cretaceous

Massive thick skull. Pachycephalosaurus had one of the thickest skulls of any dinosaur, with bone up to 10 inches thick on top of its head. Scientists think it may have used its dome-shaped skull like a battering ram when fighting with other dinosaurs.

Pretty big but not huge. This dinosaur was about 15 feet long and weighed as much as a small car (around 370 to 450 kilograms). For a meat-eating dinosaur, it was medium-sized compared to giants like T-rex.

Lived in western North America. Pachycephalosaurus roamed what is now Montana, South Dakota, Wyoming, and Alberta during the very end of the dinosaur age, called the Maastrichtian.

Known from rare fossils. Scientists know about this dinosaur mainly from one skull and a few thick skull pieces that were found. This makes it harder to know exactly what the rest of its body looked like.

Mystery about a relative. Another dinosaur called Stygimoloch might have been a younger Pachycephalosaurus or a different species entirely, but scientists aren't totally sure yet.