Stegoceras dinosaurs were a kind of pachycephalosaurid (dome-headed) dinosaur. In pachycephalosaurs, the top of the skull was remarkably thick—up to 5 cm (2 in.). This gives the skull a distinctly dome-like shape.
Stegoceras was the first pachycephalosaur to be described. When this genus was identified in 1902, it was named for the thickened part of its skull. It was originally thought that the thickness was from the core of a horn that was no longer present, and that the dinosaur was a kind of ceratopsian. Accordingly, the name Stegoceras was based on the combination of Greek words for "horn" and "roof". It was later determined that the dome was simply an effect of thickened skull bones.
The function of these thickened skulls is a matter of debate amongst palaeontologists. One suggestion is that they were used in head-butting contests, much like bighorn sheep of today.
Although worn fossils of pachycephalosaur cranial domes are frequently found, skeletons are very rare. As of 2008, only one skeleton of Stegoceras validum has been found. It was found in Alberta and excavated in the 1920s. Only two other pachycephalosaur skeletons have been found, and they were found in Mongolia.
In general, pachycephalosaurs were relatively small dinosaurs. Stegoceras weighed in the order of 55 kg (121 lb.) and was about 2 m (6.5 ft.) long.
Stegoceras lived during the latter part of the Late Cretaceous Period.
There are two species in the genus Stegoceras: Stegoceras validum and S. edmontonese.