.42" Fossil Pachycephalosaurid Tooth - Judith River Formation

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 Judith River Formation is one of the world's most prolific sources of Late Cretaceous vertebrate fossils. At least sixteen Orders containing more than forty Genera are known from the formation. These include fish, amphibians, mammals, and insects in addition to reptiles and avian (birds) and non-avian dinosaurs. Among the more interesting specimens is Leonardo, a mummified and fossilized Brachylophosaurus. This is a hadrosaur, a duck-billed dinosaur found with amazing soft-tissue preservation: skin impressions can be found on 90 percent of its body! The pattern in the skin on its feet is even preserved. In addition to Leonardo, the Judith River Formation contains the remains of the theropod Hesperornis, the only known freshwater Hespernorthid, a penguin-like bird.