Although named in 1983, the first Stygimoloch specimen was a cluster of bumps around a single horncore described in 1896. It was originally believed to be a spike from the back or tail of Triceratops. When good remains of pachycephalosaurs (bone-headed dinosaurs) were first found in the 1940's, this horncore was referred to the genus Pachycephalosaurus. When Galton & Sues described Stygimoloch, they realized this fossil had come from the rear right side of a S.spinifer skull.

Pachycephalosaurs have long been depicted in dramatic head-butting contests over mates or territory. The rather narrow dome of Stygimoloch, however, is far from an ideal shape for head-to-head collisions. The narrowing of Stygimoloch's dome and the extensive development of the nodes and horns surrounding it may represent a trend towards visual intimidation and away from physical confrontations as a means to solve questions of pachycephalosaur social status.