Main Group: Marginocephalian Dinosaurs

Time: Late Cretaceous

Size: 16 1/2 ft (5 m) long

Fossil Finds: North America

Pachycephalosaurus (1)

Fossil Skull of an Adult

Pachycephalosaurus (2)

Fossil Skeleton of a juvenile

Of the group of dinosaurs known as pachycephalosaurs ("Bone Headed Dinosaurs"), Pachycephalosaurus was the largest. Two other pachycephalosaurian species, Dracorex and Stygimoloch are now considered different growth stages of Pachycephalosaurus.