Name: Stegoceras ‭(‬horned roof‭)‬.
Phonetic: Steg-oh-seh-rass.
Named By: Lawrence Lambe‭ ‬-‭ ‬1902.
Synonyms: Ornatotholus,‭ ‬Hanssuesia‭?
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Ornithischia,‭ Pachycephalosauria.
Species: S.‭ ‬validum‭ (‬type‭)‬,‭ ‬S.‭ ‬novomexicanum.
Diet: Herbivore.
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.

       Stegoceras is one of the more common and better known pachycephalosaurs,‭ ‬and one 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 ‬Pachycephalosaurus.
       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.

Further reading
-‭ ‬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.
- Squamosal Ontogeny and Variation in the Pachycephalosaurian Dinosaur Stegoceras validum Lambe, 1902, from the Dinosaur Park Formation, Alberta. - Journal of Vertebrate Paleontology. 32 (4): 903–913. - R. K. Schott & D. C. Evans - 2012.


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