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Stegoceras validum

Stegoceras is certainly one of nature's strangest creations. These small Cretaceous dinosaurs (1.5-2 meters long) sported a large, domed, bony head that was bordered with small bony knobs and protrusions around the base. Skeletal analysis indicates that Stegoceras walked on two legs and carried their heads dome-forward and nose down. They used their stiff tails as a counter balance. Current thinking among experts describes Stegoceras as an animal that used its head to butt into the flanks of other animals and that this activity was probably used to defend territory and maintain their social structure not unlike how head butting functions in modern bighorn sheep herds. Some evidence suggests that males had larger and more elaborate domes than females and that the dome structure thickened with age and maturity.

Stegoceras was a plant eater that lived in the inland (rather than in coastal) environments of western North America. It was a contemporary of plant-eating hadrosaurs, ceratopsians and ankylosaurs along with the predatory tyrannosaurs of that time.

Taxonomy
Stegoceras validum is an ornithischian dinosaur and within that group, a marginocephalian. Pachycephalosaurs are then grouped as either primitive or advanced. Stegoceras is one of the11 species or types of the advanced pachycephalosaurs found so far. Another well know member of this group is the much larger Pachycephalosaurus wyomingensis.

Advanced pachycephalosaurs are distinguished by their enlarged, domed, bony skulls. Most of our information comes from these skulls, and except for Stegoceras, few other bones have been found. The skeletal remains of Stegoceras support the head butting hypothesis: thickened skull; shortened base of the skull; angle of the skull relative to the spine; the expanded width of the back of the skull; the fusing and strengthening of the vertebral column (spine); and the reinforced hip socket. It's a pretty convincing picture of an animal that used it head in social or ritual combat.

Pachycephalosaur evolution paralleled that of their ceratopsian cousins. Early primitive species show up in Asia with limited diversification (sharing time and space with Protoceratops) and then an expanded population of types appear later in western North America along with the large Late Cretaceous ceratopsians. Stegoceras fossils are rare because they lived in inland environments where fossilization is less common.

Stegoceras Links

Excellent pachycephalosauria cladogram

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