Pachycephalosaurs

Pachycephalosaurs were the "bone-headed" dinosaurs. They had great big heads with a thick boned on the tops. These bones might have been used to ram into each other like some animals do today. This big thick bone was the perfect type to absorb shocks well. The skull made them look kind of like they had a large brain, but it was all bone. Their actual brain was not very big. Skeletons of these dinosaurs are very rare (usually only the big thick part of the skull is found). Recently, a good skeleton was found. More information about it is going to be published, but has not been yet. Maybe the new skeleton will tell us more about what that big head was used for.

There are two basic types of Pachycephalosaurs: Pachycephalosaurids (which had round heads) and Homalocephalids (which had flat heads). They are found so far in North America and Asia (with a possible one from Europe). Both of those continents have good areas to find dinosaurs, so it might just be that they have not been found in other places yet.

Pachycephalosaurids

The round headed Pachycephalosaurids are the most commonly found ones. They are the only ones to be found in North America. One type (Stegoceras) is found quite frequently in Alberta, but usually as just the skull cap. A few are known from Asia, where they are more rare. There is a lot of argument over whether the round skulls would be able to hit head-on in a collision, like Big Horned Sheep. Many scientists think that the round heads would not hit properly and the two animals would hurt themselves more than the intended target.

Most Pachycephalosaurids are known from just the skull cap (Gravitholus, Stygimoloch, Yaverlandia, and Ornatholus) but a fairly complete skull has been found for Pachycephalosaurus. Good skulls and skeletons have been found for Prenocephale, Stegoceras and the new specimen. With the information that we have, sizes range from 2 meters (Stegoceras) to about 5 meters or more for Pachycephalosaurus.

Homalocephalids

The flat headed Homalocephalids are only found in Asia so far. They are know from quite a bit of the skeleton. Scientists think that they pushed each other when they were head to head, rather than running and head butting. This makes sense because the skull roof was not quite as this, so they did not have as much protection.

Homalocephlids are about 2 meters long. Homalocephale and Goyocephale are known from skeletons with skulls from Mongolia, but Wannanosaurus, from China, is only known from a partial skull with a small amount of skeleton.

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