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.

The Hell Creek Formation

Renowned for both its age and rich sedimentary layers, the Hell Creek Formation is one of the most intensively studied fossil-bearing regions on Earth. To date, scientists have documented 158 genera of animals and 64 genera of plants from its rocks, with new finds emerging regularly. Beyond iconic dinosaurs such as tyrannosaurs, ceratopsians, and hadrosaurs, the formation has produced an extraordinary array of life, including amphibians, reptiles, lizards, snakes, turtles, fish, sharks, birds, and early mammals. Together, these fossils provide the most complete picture of the ecosystems that thrived just before the Cretaceous–Paleogene extinction event.