Which dinosaur is known for its thick, domed skull for head-butting?

The dinosaur known for its thick, domed skull used in possible head-butting was Pachycephalosaurus. Its name means “thick-headed lizard,” a reference to the remarkably reinforced dome formed by the skull roof.

Pachycephalosaurus lived in western North America during the Maastrichtian Age of the Late Cretaceous, roughly 72–66 million years ago. It was a bipedal herbivore about 4.5 meters long, with a bulky body, long hind legs, and a short, thick neck.

Scientists have long proposed that the dome was used in contests between individuals, similar to head-butting in bighorn sheep. However, the exact behavior remains debated: some research supports direct head-butting, while other studies suggest flank-butting, display, or species recognition. The related names Dracorex and Stygimoloch may represent growth stages of Pachycephalosaurus rather than separate genera.