Stygimoloch: Prehistoric Beast of the Week

Halloween is so close!  In honor of my favorite holiday let's check out a dinosaur with a truly horrifying name.  Enter Stygimoloch spinifer!  The genus name, Stygimoloch, translates to "Demon from the River of Death". (called "Styx" in Greek mythology.)  The name is in reference to this dinosaur's rather demonic-looking horns, which covered a lot of its head.  Despite the name and appearance, Stygimoloch was a plant-eater, not a soul-eating beast from the underworld.  Stygimoloch measured about ten feet long from beak to tail and lived during the very end of the Mesozoic in what is now the United States, between 67 and 66 million years ago, during the Late Cretaceous period.  When alive, it lived alongside Tyrannosaurus, Triceratops, Troodon, Anzu, Anatotitan, Ankylosaurus, Pachycephalosaurus, Dracorex, and Quetzalcoatlus.

Stygimoloch spinifer life reconstruction by Christopher DiPiazza.

 Stygimoloch is obviously most noted for it's head, which was practically covered in horns.  Many of the horns, especially on the snout and around the eyes, were small.  On the back of the head were two sets of long horns growing from either side of the rear of the skull.  On the top of the head, Stygimoloch was armed with a small oval-shaped mass of solid bone.  Paleontologists debate as to what exactly all of this interesting ornamentation was for.  Many believe they were weapons, and that Stygimolochs would have rammed or pushed each other for dominance, or possibly defended themselves against predators with their heads.  Others believe they were only for display.

Stygimoloch skull on display at the Museum fur Naturkunde in Berlin.

Stygimoloch also had a relatively long snout, tipped with a short beak.  This beak was probably good for clipping soft vegetation, which would have then been shredded up in the back of the mouth with its small teeth.  Some suggest Stygimoloch and its relatives would have actually eaten meat in addition to plants in the form of small animals or possibly carrion, but currently know actual evidence supports this idea.  Stygimoloch also had large eye sockets and likely had good vision, which is common to members of its family, the pachycephalosaurids. 

Relatively recently, some paleontologists have suggested that Stygimoloch was actually the same species as Dracorex and Pachycephalosaurus.  According to this hypothesis, Dracorex was a juvenile Pachycephalosaurus, having not developed a dome in its young age, Stygimoloch would have been a young adult, having developed a small dome, and Pachycephalosaurus was the mature adult, with a full dome but shorter horns.  Despite this idea's popularity, it is highly debatable and challenged by many other paleontologists.  The idea of long horns being absorbed into a thickening skull needs to be looked into more since nothing like it can be observed in any other large vertebrate. 

References

Carpenter, Kenneth (1997). "Agonistic behavior in pachycephalosaurs (Ornithischia:Dinosauria): a new look at head-butting behavior". Contributions to Geology 32 (1): 19–25.

Galton, P. M. and H. D. Sues (1983). "New data on pachycephalosaurid dinosaurs (Reptilia: Ornithischia) from North America." Canadian Journal of Earth Sciences 20: 462-472.

Goodwin, M. B., E. A. Buchholtz, et al. (1998). "Cranial anatomy and diagnosis of Stygimoloch spinifer." Journal of Vertebrate Paleontology 18(2): 363-375.

Horner J.R. and Goodwin, M.B. (2009). "Extreme cranial ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus." PLoS ONE, 4(10): e7626.

Maryańska, Teresa; Chapman, Ralph E.; Weishampel, David B. (2004). "Pachycephalosauria". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 464–477. ISBN 0-520-24209-2.