[D] Stegoceras validum [Su] [T]
Cretaceous Late Campanian
Ornithischia Genasauria Cerapoda Marginocephalia Pachycephalosauria Pachycephalosauridae
Judith River Group (Wedge), Alberta, Canada; Judith River Formation (Wedge), Montana, Fruitland Formation, San Juan Basin, New Mexico, US
Typespecies - Skull
Stegoceras (Lambe, 1902) > Stegoceras validum (Lambe, 1918) >> Stegoceras breve (Lambe, 1918)
Stegoceras > Stegoceras edmontonense (Brown & Schlaikjer, 1943) > Troodon edmontonensis (Brown & Schlaikjer, 1943)
Stegoceras > Ornatotholus (Galton & Sues, 1983) >> Stegoceras browni (Wall & Galton, 1979) >> Ornatotholus browni (Wall & Galton, 1979)
Stegoceras > Stegoceras novomexicanum (Jasinski & Sullivan 2011)
Stegoceras validum (sensu stricto) is a primitive, incipiently-domed pachycephalosaur that is characterized by a well-developed squamosal shelf and open supratemporal fossae. It is the sister taxon to the fully-domed Pachycephalosaurinae. Specimens consisting of flat, paired frontals are immature individuals of Stegoceras validum. The taxon Ornatotholus browni has a parietal and displays features identical to Stegoceras validum and is therefore a subjective junior synonym. (Sullivan, 2003 )
Stegoceras (\\\\\\\"Horny roof\\\\\\\") was a gaot-sized pachycephalosaurid known from one partial skeleton and dozens of mostly partial skulls. The skulls evidently became thicker and higher with age, especially in males. A male\\\\\\\'s dome overgrew the bony skull shelf.
Stegoceras was about 2.4 m (8ft) long, and lived in Alberta (Canada) and Montana (US) in the Late Cretaceous. The reason several species of Stegoceras were originally described as Troodon was that this genus was erroneously equated with Troodon due to the occurrance of associated Troodon teeth.
Fruitland Fm. NMMNH P- 33893, nearly complete juvenile frontoparietal
The frontoparietal measures 75 mm in length along the midline. Dorsally, the posterior portion of the frontal region is the thickest, forming an incipient dome that is approximately 20 mm high and is positioned slightly anterior to the frontoparietal suture on the ventral side. The dorsal surface is pitted and has a distinctive, node-like textural surface. The parietal portion of the frontoparietal is depressed posteriorly, and the median section of the parietal extends posteriorly 15 mm beyond the anterior- most margin of the supratemporal fossae. This parietal projection laterally adjoins, on both sides, the left and right supratemporal fossae, and thus participates in the formation of the parietosquamosal shelf.
The anteromedial margin of the right supratemporal fossa is welldefined, whereas the left is less so, suggesting that the left supratemporal fenestra may be less well-developed, as it does not to appear to be damaged. The sutural surface on the posterior part of the right squamosal, coupled with the prominent median extension of the parietal and welldeveloped parietosquamosal shelf. Both squamosals are missing. The sutural surfaces for the anterior supraorbital, posterior supraorbital, and postorbital, are nearly complete on the right, with damage between the posterior supraorbital and postorbital resulting in a gap between the two. Only the left postorbital sutural surface is preserved, and both left supraorbital surfaces are damaged.
Anteriorly, both the left and right prefrontal sutural surfaces are present with the medial nasal surfaces. The sutural surfaces vary in height, between 5-10 mm, along the periphery of the frontoparietal. Ventrally, the frontoparietal suture is distinct, and it rises dorsally into the damaged lateral surfaces mentioned above. Laterally, the roof of the right orbit is preserved, while that of the left is obstructed with matrix. Anteriorly, the impression of the dorsal surface of the olfactory bulbs is evident; so, too, is that of the cerebrum and cerabellar regions posteriorly. The cerabellar region is confined to the parietal portion of the frontoparietal. The dorsal surfaces of the supratemporal fossae are preserved on both sides of the parietal, and both diverge anteriorly from the sagittal plane. The dorsal surface of the median parietal projection is relatively flat and smooth. (Sullivan, R.M. and S.G. Lucas. 2006.)