Pachycephalosaurus Dome FragmentPachycephalosaurus was a Late Cretaceous dinosaur with a unique feature: its skull had a battering ram like bone plate. This several inch thick helmet of bone allowed it to absorb blunt force when it struck its head against surfaces. This specimen is a piece of a Pachycephalosaurus skull dome fossil recovered from the Hell Creek formation in South Dakota. It's estimated to be over 66,000,000 years old. Both small and medium sized fragments are