modified to appear fang-like. These teeth may have been used for gripping food, which would be chewed with the triangular cheek teeth. They also noticed that the wide rib cage and anatomy of the spinal column and pelvis suggested that the fermentation of ingested plant matter happened farther along in pachycephalosaurs' digestive tracks than in ceratopsians and ornithopods. 1997 Sereno named the Marginocephalia, a clade consisting of the pachycephalosaurs and ceratopsians. Chapman and others observed that Stegoceras validum is one of the best documented case of sexual dimorphism among dinosaurs. Carpenter elaborated on Sues' 1978 argument that pachycephalosaurs were more likely to use their skull domes to butt flanks rather than heads. Alexander reiterated his argument that since the forces generated by pachycephalosaurs head-butting were probably smaller than previously expected and "glancing blows" sustained on impact presented little risk of harm to the animals involved; thus head-butting was the likely function of the pachycephalosaur dome. 1998 Scott Donald Sampson and others realized that Majungatholus atopus was actually a theropod. Goodwin and others argued that the shelf on the skulls of some specimens of Stegoceras validum might indicate the specimen's immaturity rather than its gender. They also argued against the reconstruction of the skull of Stygimoloch used by Carpenter the previous year that led him to support the idea that pachycephalosaurs butted flanks. They argued that the bone of the skull dome was too rich in blood vessels to function as a battering ram, but instead was probably purely for display. They suggested that the evolution of the use of pachycephalosaur skull domes may parallel the evolution of agonistic behavior in certain mammalian lineages, where more primitive forms engaged in flank butting which gave way to head butting and culminated in purely ornamental structures. Goodwin and Horner studied the microstructure of the dome of Stygimoloch and Stegoceras. They reiterated their argument that the bone was too rich in blood vessels to withstand the kinds of forces generated by head or flank butting. This vulnerability would apply just as well to collisions impacting the side of the skull as well as front-on. Chapman and others used 3D digital scans of pachycephalosaur domes to study whether or not their anatomy was suited for use in head-butting between members of the same species. They found that even pachycephalosaurs with very round skull domes had sufficient surface area for head-butting with little risk of charges ending in dangerous "glancing blows". 21st century 2000s 2002 Williamson and Carr described the new genus and species Sphaerotholus bucholtzae. He also described another species in that genus, S. goodwini. 2003 Sullivan described the new genus Colepiocephale to house the species Stegoceras lambei. He also erected the new genus Hanssuesia to house the species Troodon sternbergi. 2005 A. O. Averianov, T. Martin, and A. A. Bakirov described the new genus and species Ferganocephale adenticulatum. 2006 Sullivan described the new genus and species Alaskacephale gangloffi. Bakker and others described the new genus and species Dracorex hogwartsia. 2010s 2010 N. R. Longrich, J. Sankey, and D. Tanke described the new genus and species Texacephale langstoni. 2011 Watabe, Tsogtbaatar and Sullivan described the new genus and species Amtocephale gobiensis. Jasinski and Sullivan described the new genus and species Stegoceras novomexicanum. 2013 Evans and others described the new genus and species Acrotholus audeti. See also History of paleontology Timeline of paleontology Timeline of ceratopsian research Timeline of troodontid research Footnotes References External links Category:Pachycephalosaurs pachycephalosaur