Pachycephalosaurus skull section

Pachycephalosaurus is the dinosaur with the large domed skull which is surrounded by bony nodes or spikes, and it names means “thick-headed lizard” that lived during the late Cretaceous period in North America. The domed skull is quite thick (up to 10 inches) and believed that it may have been used in intra-species combat. Many fossilized skulls have been found with healed wounds. Pachycephalosaurus was a bipedal dinosaur that grows to 15 feet and 2000 lbs, and the largest of the Pachycephalosaur dinosaurs. Other named Pachycephalosaurs found in the Hell Creek Fm. include Dracorex and Stygimoloch. Dracorex and Stygimoloch, which exhibit much smaller domes and much larger spike ornamentation, are now believed to be early growth stages of Pachycephalosaurus. Only one species exists which is Pachycephalosaurus wyomingensis. 

Pachycephalosaurus fossils are quite rare. In fact, only one partial skeleton has been found. A dinosaur census conducted by the Hell Creek Project calculated relative abundance of the Pachycephalosaurus was 1% of the population. Today, we find fossilized teeth, unguals (claws), spikes, and non-associated bones.

Pachycephalosaurus spikes or nodes. Pachycephalosaurus dinosaurs are known for their large domed skull tops which is an extremely thick bone and a skull that was ornamented with “spikes” and “nodes” giving them a one-of-a-kind appearance. The Pachy spikes and nodes are not attached to the skull, but are actual skull elements that often found as segments of skull with nicely articulated surfaces on top and bottom. So, the skull pieces would come from a Pachycephalosaurus that passed away. The largest spikes or horns are found on the back of the neck of the early Pachycephalosaurus growth stages referred to  Dracorex and Stygimoloch. The Pachy spikes and nodes are quite rare and highly collectable.