is the last, largest, and most famous member of the Pachycephalosauria, or thick-headed dinosaurs. In the 1970s paleontologist Peter Galton proposed that male pachycephalosaurs used their dome heads as battering rams, like Bighorn sheep. The idea caught the public’s imagination, and two individuals are seen doing this in The Lost World: Jurassic Park
(of course, these are genetically engineered dinosaurs and not necessarily exactly the same ones that lived 70 million years ago!). But by the 1990s, scientists began to question Galton’s head butting theory. It was pointed out that animals who do butt heads have a wide surface area where the heads come into contact to prevent “head slippage.” This happens when two animals butt heads at high speed and do not hit straight on. The risk breaking their necks when their heads suddenly snap to one side. Pachycephalosaurus
has a domed, or rounded, head, which would minimize surface contact and therefore increase the risk of head slippage. This throws doubt on the idea of any high speed head-butting between pachycephalosaurs, but it does not exclude “head-pushing” of “head-ramming” against non-pachycephalosaurs.