Pachycephalosauria
Ornithischia Genasauria Cerapoda Marginocephalia Pachycephalosauria [Herbivore]
All marginocephalians closer to Pachycephalosaurus than Triceratops (Sereno, 1986)
Small to medium sized obligarorily bidepal ornithischians from the Early to Late Cretaceous. Pachycephalosauria is the infraorder of “thick-headed” Marginocephalia dinosaurs. The Pachycephalosauria are divided in to two families. The Pachycephalosauridae (dome-headed) who had a marked dorsoventrally thickening of the frontoparietal (forehead) bones of the skull as a distinctive feature, and Homalocephalidae (flat-headed).
Sereno (1986) defined Pachycephalosauria, along with Ceratopia, as the two major nodes whitin Marginocephalia. The \"dome-headed\" were strange bideps with helmet-like skulls, which were up to 25 cm thick. By comparison, a human skull is only 0.64 cm thick.There are strong indications that the thickness of the skull increased as the animal grew older.
The idea that pachycephalosaurids have been headbusters is outdated most scientist now believe it was just for sexual display. The fact that there is no histological evidence of the bone being damaged by trauma supports this idea. (Goodwin, M., E. Buchholtz, and R. Johnson, 1998, JVP 18(2):363-375; Horner, J. and M, Goodwin, 1998, JVP 18(3):52A).
Numerous other uniquely derived characters in the skull and postcranial skeleton clearly support the monophyly of this infraorder. (Maryanska and Osmolska, 1974; Sereno, 1986; Sues and Galton, 1987) Pachycephalosaurs retain several primitive features. The teeth of the heterodont dentition are quite small. The margins of the mediolaterally compressed, somewhat leave-shaped crowns of the maxillary and posterior dentary teeth bear distinct denticles. The premaxilla retains teeth. Also, the ischium lacks an obturator process.
Time-Geolist - Alfabetic list
Jurassic Middle
Kyrgyzstan
Ferganocephale adenticulatum - Balabansai Formation
Cretaceous Early
England
Yaverlandia bitholus - Wealden Beds, Wessex Formation
Cretaceous Late
Canada
Colepiocephale lambei - [Foremost Formation], Judith River Wedge
Stegoceras lambei - [Foremost Formation], Judith River Wedge
Gravitholus albertae - Judith River Group (Wedge)
Stegoceras - Canada US
Ornatotholus browni - Judith River Group (Wedge)
Stegoceras breve - Judith River Wedge
Stegoceras browni - Judith River Group (Wedge)
Stegoceras edmontonense - Horseshoe Canyon Formation
Stegoceras validum - Judith River Group (Wedge)
Troodon edmontonensis - Horseshoe Canyon Formation
US
Alaskacephale gangloffi - Prince Creek Formation, Alaska
Dracorex hogwartsia - Hell Creek Formation, South Dakota
Hanssuesia sternbergi
Stegoceras sternbergi
Troodon sternbergi
Pachycephalosaurus
Pachycephalosaurus grangeri
Pachycephalosaurus reinheimeri - Judith River Formation, (Wedge)
Pachycephalosaurus wyomingensis - Lance Formation, Hell Creek Formation, Judith River Formation (Wedge)
Troodon wyomingensis - Lance Formation
Tylosteus ornatus - Black Foot Country
Sphaerotholus buchholtzae - Hell Creek Formation
Sphaerotholus goodwini - Kirtland Formation
Stegoceras - Canada US
Stegoceras validum - Judith River Formation (Wedge), Fruitland Formation
Stegoceras edmontonense - Hell Creek Formation
Stegoceras novomexicanum - Fruitland Formation, Kirtland Formation
Stygimoloch spinifer - Hell Creek Formation, Lance Formation
Stenotholus kohleri - Hell Creek Formation
Texacephale langstoni - Aguja Formation, Texas
China
Heishansaurus pachycephalus - Minhe Formation
Micropachycephalosaurus hongtuyanensis - Wangshi Series
Troodon bexelli - Minhe Formation
Wannanosaurus yansiensis - Xiaoyan Formation
Mongolia
Amtocephale gobiensis - Baynshirenskaya Svita
Goyocephale lattimorei - Unnamed unit, Ovorkhangai
Homalocephale calathoceros - Nemegt Formation
Prenocephale prenes - Nemegt Formation
Tylocephale gilmorei - Barun Goyot Formation