Pachycephalosaurus wyomingensis was the largest of the pachycephalosaurids—"thick-headed dinosaurs"—which featured extremely thick skullcaps. The top of a Pachycephalosaurus skull could be 9 ...

Pachycephalosaurus, the delicately built, 15-foot-long, dome-headed dinosaur that lived alongside Tyrannosaurus and Triceratops, is a staple of children’s books and popular culture—one usually ...