Stygimoloch (STIG-ih-MOE-lock) is a putative genus of the pachycephalosaur family living in the early Cretaceous period. It was distinguished from other pachycephalosaurs by the row of spikes on the back of its head, behind the dome characteristic of the family. Jack Horner has presented evidence in 2009 (and others after him) that suggests that Stygimoloch might be the juvenile form of Pachycephalosaurus.
In the Jurassic Park Franchise
It is revealed that there are surviving Stygimoloch populations on Isla Nublar, although they now face the impending danger of a volcanic eruption, alongside many other creatures, in the form of an erupting volcano. At least one Stygimoloch (nicknamed Stiggy) was rescued from the island, and later brought to Lockwood Manor to be auctioned. After Owen Grady and Claire Dearing were trapped in a cell adjacent to Stiggy's, Owen managed to get her to bust down the wall between them and bust open the cell. She then rampaged through the ongoing auction after escaping the cell block, and later escaped into the forest.