Name meaning: "Thick-Headed Lizard"
Height: 2 metres (6 ft)
Length: 5 metres (16 ft)
Weight: 450 kilograms (990 lb)
Pachycephalosaurus 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. In The Lost World: Jurassic Park, you can even see the dome-headed pachycephalosaurs doing head butts (of course, these are genetically engineered dinosaurs and not necessarily exactly the same ones that lived 70 million years ago!). Like other pachycephalosaurids, Pachycephalosaurus was a bipedal omnivore with an extremely thick skull roof. It possessed long hindlimbs and small forelimbs. The thick skull domes of Pachycephalosaurus and related genera gave rise to the hypothesis that pachycephalosaurs used their skulls in intra-species combat.
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.
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