page_title: Timeline of pachycephalosaur research
section_title: 1990s
hierarchical_section_title: Timeline of pachycephalosaur research / 20th century / 1990s
caption_attribution_description: Español: Reconstrucción de un busto de Stygimoloch
context_page_description: This timeline of pachycephalosaur research is a chronological listing of events in the history of paleontology focused on the pachycephalosaurs, a group of dome-skulled herbivorous marginocephalian dinosaurs. One of the first major events related to the history of pachycephalosaur research actually regards the discovery of an unrelated dinosaur called Troodon, reported from the western United States by Joseph Leidy in 1856. The type specimen of Troodon was simply an unusual tooth, but the close resemblance between Troodon teeth and pachycephalosaur teeth would cause taxonomic confusion for over a century. This was resolved by Phil Currie in 1987, who realized that Troodon belonged to a group of bird-like carnivores then known as saurornithoidids, but since renamed Troodontidae after Troodon itself. The first scientifically documented true pachycephalosaur remains were discovered in Early Cretaceous rocks from England and named Stenopelix not long after Troodon was named in America. Other notable early finds include the well-known pachycephalosaur Stegoceras validum.
context_section_description: 1990
  Maryańska followed Dong's 1978 suggestion, which had also been supported by Sues and Galton in 1987, that the Pachycephalosauria contained two families, the Homalocephalidae, which had flat heads, and the Pachycephalosauridae, which were characterized by the famous domed skulls.
  Chapman published a morphometric analysis of pachycephalosaur skulls.
  Mark Goodwin published a morphometric analysis of pachycephalosaur skulls.
  1996
  David Fastovsky and David Weishampel examined the paleobiology and paleoecology of pachycephalosaurs in detail. They observed that pachycephalosaurs had differing teeth in different regions of the jaw. The front teeth were peg-like, sometimes the last of these front teeth was 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".
caption: Artist's restoration of Stygimoloch
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