Means: Styx Demon

Period: Late Cretaceous, 68-66 Million Years Ago

Region:  Montana, Wyoming and North Dakota (USA)

In 1973, scientists from the Unive‎rsity of California Berkeley, whilst exploring Hell Creek Formation exposures in McCone County, Montana, found a single, robust skull fragment with the remains of three distinct, prominent horns projecting out of the back of it.

Although classified as a bone from a pachycephalosaur, no further work on the bone was carried out until palaeontologists Hans-Dieter Sues and Peter Galton published a comprehensive review of North American pachycephalosaur fossils in 1983.  They named Stygimoloch based on this unusual skull bone and other fragmentary material that had once been thought to represent part of the neck frill from a Triceratops.

A paper presented at the 2007 annual meeting of the Society of Vertebrate Paleontology suggested that the spiky Stygimoloch was not a valid species of dinosaur, but its fossils represented juveniles of the already described and much larger, bone-headed dinosaur Pachycephalosaurus.