2.8" Pachycephalosaur Dorsal Vertebra - South Dakota

Pachycephalosaurs are a family of bipedal dinosaurs that lived during the Late Cretaceous and had a distinctive, large, bony dome on top of their skull. This dome was sometimes up to 10 inches thick and was thought to cushion their brain from impacts. Some paleontologists believe this thick skull may have been used for head-butting, much like modern rams, while others contend it may have been a sexual display. They were either an herbivore or omnivore with small leaf-shaped teeth effective for shredding plants.

There are more than a dozen described genera of Pachycephalosaurs, though Pachycephalosaurus from the Hell Creek Formation is the best known.

Because of its age and sedimentary composition, the Hell Creek Formation has become one of the most paleontologically studied areas in the world. 158 genera of animals and 64 genera of plants are known from the formation and new discoveries are made frequently. In addition to Tyrannosaurs, Ceratopsids, and Hadrosaurs, the formation has yielded remains of amphibians, reptiles, lizards, snakes and turtles, fish and sharks, avian and non-avian dinosaurs, and mammals. The Hell Creek Formation gives the most complete understanding of the environment just before the Cretaceous-Paleogene extinction.