the domed heads of pachycephalosaurs were used as "battering ram[s]". 1956 Science fiction author Sprague de Camp was the first to specifically suggest that pachycephalosaurs used their domed heads to butt heads with other pachycephalosaurs. 1961 1961 Russian paleontologist Leo Shiovich Davitashvili suggested that pachycephalosaur skull domes were employed in mating displays or "combat" independently of Western science. 1969 Colbert reiterated his earlier suggestion that pachycephalosaurs used their domed heads as "battering ram[s]". 1970s 1971 Peter Malcolm Galton began fleshing out the hypothesis that pachycephalosaurs engaged in head-butting. Robert T. Bakker illustrated the hypothesis. Galton argued that Brown and Schlaikjer got the genders wrong in their 1943 hypothesis that Stegoceras validum exhibited sexual dimorphism. Under Galton's interpretation, as Stegoceras grew the dome expanded until there was no prominent shelf. The presence of a shelf was therefore more likely to suggest a less developed dome, as might be expected in a female morph. He continued to advocate for the idea that pachycephalosaurs butted heads. He observed that many aspects of pachycephalosaur anatomy seemed adapted to transmitting forces received from a blow to the head through the body. 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. 1974 Teresa Maryańska and Halszka Osmólska named the suborder Pachycephalosauria. Maryańska and Osmólska described the new genus and species Homalocephale calathocercos. They also described the new genus and species Prenocephale prenes. The authors noted that past discussions in the literature about whether or not the presence of a shelf of bone on the skull was a gender difference was relevant to the validity of these new taxa since one had a shelf and the other did not. As these genera came from the same time and place, it was possible that instead of being different taxa, one could be the male and the other the female of a single species. However, Maryańska and Osmólska noted many anatomical differences that supported their status as distinct taxa. They therefore described the new genus and species Tylocephale gilmorei. The researchers observed that teeth of different pachycephalosaur species exhibit different wear patterns. This suggests that there was significant variations of diet between species. They observed that many aspects of pachycephalosaur anatomy seemed adapted to transmitting forces received from a blow to the head through the body. 1977 Hou Lianhai described the new genus and species Wannanosaurus yansiensis. Ralph Molnar "reiterated" the idea that pachycephalosaur domes were used in mating displays or combat. 1978 Dong Zhiming described the new genus and species Micropachycephalosaurus hongtuyanensis. He also proposed that the flat-headed pachycephalosaurs constituted a distinct family called the Homalocephalidae. Hans-Dieter Sues argued that while pachycephalosaurs probably did use their skull domes as battering rams, they probably did not use them in direct head-to-head contact because the domes lacked a mechanism to prevent the combatants skulls from sliding past each other at odd angles upon impact. Sues examined pachycephalosaur head-butting experimentally using photo-elastic plastic models studied under polarized light. His results were consistent with the head-butting hypothesis, but he felt it more likely that pachycephalosaurs would use their domed heads to ram each other's flanks. He observed that many aspects of pachycephalosaur anatomy seemed adapted to transmitting forces received from a blow to the head through the body. 1979 William Patrick Wall and Galton described the new species Stegoceras browni. This was one of the last research publications to take seriously a hypothetical evolutionary affinity between pachycephalosaurs and ornithopods. Wall and Galton described the new genus