page_title: Timeline of pachycephalosaur research
section_title: 1980s
hierarchical_section_title: Timeline of pachycephalosaur research / 20th century / 1980s
caption_attribution_description: English: Skeletal reconstruction of Goyocephale lattimorei.
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: 1981 
  Ralph Chapman and others performed a detailed statistical analysis on the relative size of dome to braincase in 23 Stegoceras validum domes and domes from 6 other pachycephalosaur taxa. They were able to account for the age and development of the specimens using the size of the braincase as an indicator. The analysis uncovered two distinct variations in dome size probably denoting dimorphism between males and females. The form with the larger dome achieved the size of this feature by having a slightly higher rate of growth relative to the braincase.
  1982
  Altangerel Perle, Maryańska and Osmólska described the new genus and species Goyocephale lattimorei.
  Perle and others followed Dong's 1978 suggestion that the Pachycephalosauria contained two families, the Homalocephalidae, which had flat heads, and the Pachycephalosauridae, which were characterized by the famous domed skulls.
  1983
  Galton and Sues described the new genus Ornatotholus to house the species Stegoceras browni. They also described the new genus and species Stygimoloch spinifer. They noted that the bone composing its skull dome was rich in blood vessels.
  Peter Dodson argued that the rarity of pachycephalosaurs in the fossil record suggests that they preferred dryer habitats farther from coasts and rivers where ceratopsians and ornithopods lived and where fossilization is more likely to occur. He also observed that many pachycephalosaur fossils show signs of damage by transport over significant distances after death. He hypothesized that this explains why skeletal remains of Stegoceras validum are so rare compared to the isolated remains of their skull domes in the Judith River Formation. The sediments he attributed to the Judith River Formation are now considered part of the Dinosaur Park Formation.
  1986
  Paul Sereno conducted the first comprehensive study of pachycephalosaur evolutionary relationships. He also named the Goyocephala and Homalocephaloidea.
  1987
  Emily Buchholtz Giffin, Diane Gabriel, and Rolf Johnson described the new genus and species Stenotholus kohleri.
  Sues and Galton conducted the second comprehensive study of pachycephalosaur evolutionary relationships. Unlike Sereno, they found that the flat-headed pachycephalosaur taxa formed a natural family called the Homalocephalidae. They further elaborated on their support for pachycephalosaurs using their skull domes for flank-butting rather than head-to-head butting.
  Currie noted traits in the teeth of Troodon that distinguished them from those of pachycephalosaurs. He split the Troodontidae off from the latter group and noted that the family Saurornithoididae, which then included many dinosaurs now considered troodontids, was actually its junior synonym.
  1989
  Robert McNeill Alexander argued that since the forces generated by head-butting in pachycephalosaurs were probably smaller than previously expected and "glancing blows" sustained on impact presented little risk of harm to the animals involved, that head-butting was the likely function of the pachycephalosaur dome after all. He also contended that the flatter domes of primitive pachycephalosaurs were actually better suited for flank-butting than the rounded domes that supposedly put their owners at risk of injury in the case of a "glancing blow" at impact.
caption: Skeletal reconstruction of Goyocephale lattimorei
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