Stygimoloch was a pachycephalosaurid dinosaur. Its name means “Styx devil”, referring to the river from Greek mythology that bounds the underworld.It had a smaller, flatter dome than other pachycephalosaurids, with more elaborate spikes around the skull.
Stygimoloch is currently known from the Hell Creek, Ferris and Lance Formations, where only juvenile specimens have been discovered.
Stygimoloch fossils have been found in regions known to be subtropical along the shoreline of the Western Interior Sea. There was no cold season, and steady amounts of rainfall buried specimens under layers of sand after they were washed downstream.