|Scientific name||Pachycephalosaurus wyomingensis|
|Home era||Late Cretaceous|
|Creature type||Bone Headed Dinosaur|
|Appearances|| Extinction Event|
A Pachycephalosaurus is attacked and killed by a T.rex in the Cretaceous, as seen by Helen and others. She states the domes where not used for head-butting, but for attracting mates.
A Pachycephalosaurus came through an anomaly int Olympic Village Park. It then chases a jogger into a building, and smashes the window, but it is unknown what happened to the jogger next. It sees it's won reflection in the windows, mistaking them for rivals, and bangs into Evan's jeep, but is scared off by Mac's motorcycle. Mac and Dylan chase it and eventually tranquilize it. However, it sneezes on Evan, causing him to later hallucinate about the Albertosaurus and Brooke. It is presumably transported back to the anomaly by Ken and Mac.
The Pachycephalosaurus was returned through the anomaly, but was then retrieved by Ken's soldiers when he and Mac left, and returned it back to the government lab. Mac and Dylan infiltrate and find the Pachycephalosaurus with half of its domed head cut open, dead, presumably to get a sample of the domed head to analyze.