Named By: Lawrence Lambe - 1902.
Synonyms: Ornatotholus, Hanssuesia?
Classification: Chordata, Reptilia, Dinosauria, Ornithischia, Pachycephalosauria.
Species: S. validum (type), S. novomexicanum.
Size: Estimated at about 2 meters long.
Known locations: Canada, Alberta - Belly River Group and Saskatchewan - Judith River Formation. USA, Montana - Hell Creek Formation, Judith River Formation, and New Mexico - Fruitland Formation - Kirtland Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Multiple individuals.
is one of the more common and better known pachycephalosaurs,
that seems to have had a range that extended from South west/central
Canada to the south western states of the USA. The genus however
seems to have been quite a bit smaller than its more famous relative
Like with all pachycephalosaurs, the skull of Stegoceras is noted for having extreme thickening which would have resulted in a dome-like structure on top of the skull. In Stegoceras the bone that would have made up the dome would be around seventy-five millimetres at its maximum thickness. The eyes are also interesting to note as the eye sockets would have faced forwards, which means that Stegoceras would have also had a fairly good degree of stereoscopic vision, meaning depth perception. Stegoceras was also once noted as the only ornithischian dinosaur to have gastralia (belly ribs), however these have now been re-examined and realised to be ossified tendons.
In 1983 a species of Stegoceras named S. browni was established as a distinct genus named Ornatotholus. This was noted as a flat headed pachycephalosur, however it now seems that the flat headed forms of pachycephalosaurs are actually the juvenile and under developed forms of the dome-headed genera which are adults. Ornatotholus is now regarded as a juvenile of and hence synonym to the Stegoceras type species S. validum.
Also like with other pachycephalosaurs Stegoceras was once popularly thought to be a ‘head butter’, the thick dome of the skull being used to deal out and absorb impacts. This is not that widely accepted anymore however with some studies suggesting the bone of the skull would have actually not been strong enough to repeatedly absorb hits, others suggesting that it was not of a correct shape to maximise impact area. Other still suggest that ‘flank butting’, where the head was used to give out impacts to the sides of animal would have been more likely given the apparent fragility of the skull.
- New genera and species from the Belly River Series (mid-Cretaceous). - Geological Survey of Canada Contributions to Canadian Palaeontology 3(2):25-81 - Lawrence Lambe - 1902.
Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior. - Contributions to Geology 32 (1): 19–25. - Kenneth Carpenter - 1997.
- Dinosaur gastralia: origin, morphology, and function. - Journal of Vertebrate Paleontology 24 (1): 89–106. - Leon P. A .M. Claessens - 2004.
- Cranial Ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria): A Quantitative Model of Pachycephalosaur Dome Growth and Variation. - PLoS ONE 6 (6): e21092. - Ryan K. Schott, David C. Evans, Mark B. Goodwin, John R. Horner, Caleb Marshall Brown & Nicholas R. Longrich - 2011.
- Re-evaluation of pachycephalosaurids from the Fruitland-Kirtland transition (Kirtlandian, late Campanian), San Juan Basin, New Mexico, with a description of a new species of Stegoceras and a reassessment of Texascephale langstoni. - Fossil Record 3. New Mexico Museum of Natural History and Science, Bulletin 53: 202–215. - Steven E. Jasinski and Robert M. Sullivan - 2011.