Period: Late Cretaceous
Order, Suborder, Family: Ornithischia, Marginocephalia, Pachycephalosauridae
Location: North America (Canada, United States)
Length: 8 feet (2.5 meters)
Stegoceras has been one of the more interesting dinosaurs, partly because of the tangle of names that have been attached to it and also because of explanations that have been attached to its domed skull.
This pachycephalosaur was first described in 1902 by Lawrence Lambe. He thought it was a new kind of ceratopsian. However, later material suggested that it was related to the stegosaurs. It was not until 1924 that paleontologists realized it was a pachycephalosaur. Then a nearly complete skull and partial skeleton were described by Charles Gilmore, but he thought it was Troodon. Finally it was correctly classified and given the name Stegoceras ("horny roof").
We know much about Stegoceras because of a good skeleton (the only other pachycephalosaur preserved with its skeleton is Homalocephale) and many partial skulls of young and adult individuals. The dome of Stegoceras was flat in young animals but became large and thick in adults. Since there are many Stegoceras domes that have become part of the fossil record, we know there are two kinds of domes among adults. The thicker, heavier domes may-have been male skulls, while the thinner, lower domes perhaps belonged to females.
Stegoceras may have used its thick dome for head-butting contests. Males would have had these contests to win females or territory. This would also explain why the male skull domes were thicker. There is other evidence that these animals had head-butting contests. The braincase, back of the skull, and backbone all show that forces were sent from the dome through the head, around the braincase, and down the backbone to the limbs. In this way, animals like Stegoceras could survive the stress of head-to-head combat, much the same way as goats and sheep of today.