Dinosaurs · Pachycephalosaur

Stygimoloch

Say it stij-i-mol-ok. The name means ‘Styx demon’.

Stygimoloch beside a person 1.75 m tall. Ticks mark every metre.Body shape drawn for this site, showing the general build of pachycephalosaurs

Length: 3 m
Diet: Plant-eater
When: Late Cretaceous67 to 66 million years ago
Fossils found in: USA
Named by: Galton and Sues (1983)
Family tree: Dinosauria › Ornithischia › Neornithischia › Cerapoda › Marginocephalia › Pachycephalosauria › Pachycephalosauridae

Where Stygimoloch sits in the age of dinosaurs.Periods from the ICS chart; dinosaur dates from the Natural History Museum

Pachycephalosaurs. Two-legged plant-eaters with thick, domed skulls. See all 8

Lived at the same time

Alamosaurus · same country
Ankylosaurus · same country
Dryptosaurus · same country
Leptoceratops · same country
Ornithomimus · same country
Pachycephalosaurus · same country
Thescelosaurus · same country
Torosaurus · same country

Other pachycephalosaurs

Dracorex Late Cretaceous
Pachycephalosaurus Late Cretaceous
Homalocephale Late Cretaceous
Tylocephale Late Cretaceous
Stegoceras Late Cretaceous
Prenocephale Late Cretaceous
Goyocephale Late Cretaceous

Source: Stygimoloch in the Natural History Museum Dino Directory, read 12 November 2026. Sizes are the museum's estimates for a typical adult. "Lived at the same time" lists dinosaurs whose dates overlap, which does not always mean they met.