Stegoceras

Stegoceras was a small, plant-eating dinosaur that had a large, thick-skulled head. This dinosaur may have butted heads with others of its kind in bone-shaking contests. Many "Stegoceras" and other pachycephalosaur fossils have been found in Alberta, Canada, and Montana, USA.
Description.
"Stegoceras" was a herding dinosaur that lived in small groups in coastal and upland regions. Running was probably its first line of defense. "Stegoceras" lived during the late Cretaceous period, toward the end of the Mesozoic Era, the Age of Reptiles, about 76-65 million years ago. "Stegoceras" was first found in 1889.
Experiments on models.
Images of the insides of "Stegoceras"' fossilised skull showed two layers of dense bone that encase a spongy sinus held apart by tiny struts, has led some scientists to doubt this interpretation.
Computer tomographic (CT) scans on the skulls of "Stegoceras", along with a variety of modern animals were used to create 3D models of the animals' heads. The team was then able to exert virtual stresses to test how the different skulls held up.
Compared to some of today's big hitters, such as the Northern American bighorn sheep, Stegoceras' head was able to withstand the most stress.