2.5" Fossil Dinosaur (Pachycephalosaurus) Skull Section - Wyoming

Pachycephalosaurus was a medium-sized herbivorous bipedal dinosaur from the Late Cretaceous in North America, most notably in the Hell Creek Formation. Pachycephalosaurus is a genus that has had much controversy taxonomically. The two contemporaneous genera Stygimoloch and Dracorex have undergone much scrutiny to determine whether they are valid species or if they are actually juvenile growth stages of Pachycephalosaurus. Most current consensus suggests that they are, making Pachycephalosaurus the predominant Pachycephalosaur of the Hell Creek Formation.

Pachycephalosaurus was a bipedal dinosaur that lived during the Late Cretaceous period and probably was about 15 feet in length.

Pachycephalosaurus had a distinctive large, bony dome on top of its skull up to 10 inches thick to cushion its 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.

It was one of the last non-avian dinosaurs before the K-T extinction event, 65 million years ago.

There is only one known species of Pachycephalosaurus, Pachycephalosaurus wyomingensis. Its remains have been found in Montana, South Dakota, and Wyoming.

It was either an herbivore or omnivore with small leaf-shaped teeth effective for shredding plants.

About The Lance Formation

The Lance Formation of eastern Wyoming is a Late Cretaceous (69–66 million years old) unit that represents the same geologic age as the famous Hell Creek Formation of Montana and the Dakotas. Although they are time-equivalent, the Lance and Hell Creek preserve subtly different environments. Hell Creek reflects a humid, forested coastal plain punctuated by volcanic ash deposits, while the Lance records a slightly drier, more open floodplain landscape with broader river systems and fewer ash layers. Together, they provide a complementary view of life in the final chapter of the dinosaur era.

Perhaps the most famous Lance resident would be Tyrannosaurus rex, the largest North American carnivore to ever live. However, other smaller theropods also roamed the American midwest in this subtropical coastal stream system, including the beaked Ornithomimus, a lanky running theropod with a build similar to a modern ostrich, as well as several small predatory troodonts such as Paronychodon and Pectinodon.

Herbivorous dinosaurs also took advantage of the abundance offered by this unique era. Armored ankylosaurs dwelt in herds, their safety assured by their numbers, their heavy bone plating protecting most of their bodies and even their eyelids, and huge bone clubs on the ends of their tails providing them with powerful offensive capabilities. Ceratopsians like the famous Triceratops also formed protective herds, guarding their necks with frills and horns. Their smaller relatives, the dome-headed pachycephalosaurs, were also well represented in the area. Hadrosaurs, duck-billed titans with huge batteries of plant-grinding teeth in elongated snouts, are also well known from the region.

In addition to dinosaurs, a wide variety of fishes, amphibians, lizards, snakes, turtles, champsosaurs, crocodilians, and pterosaurs have been found in the formation.