Dracorex

Dracorex was a dinosaur of the family Pachycephalosauridae, that lived during the Late Cretaceous of North America. The type (and only) species is Dracorex hogwartsia, meaning "dragon king of Hogwarts". It is known from one nearly complete skull (the holotype TCMI 2004.17.1), as well as four cervical vertebrae including the atlas, third, ninth and eighth. These were discovered in the Hell Creek Formation in South Dakota by three amateur paleontologists from Sioux City, Iowa. The skull was subsequently donated to the Children's Museum of Indianapolis for study in 2004, and was formally described by Bob Bakker and Robert Sullivan in 2006.

Anatomy
Dracorex, a herbivore, had a skull with spiky horns, bumps, and a long muzzle. The species also sports well-developed supratemporal fenestrae and a heavily-armored flat skull – lacking the characteristic pachycephalosaurid dome. Coupled with these two features is the excessive number of osteoderms in the form of irregular osteodermal crust: a number of nodes, larger hornlets, and spikes. Disregarding this, Dracorex is physically comparable to Stygimoloch.

In the Pachycephalosauridae family, the Asian taxa includes a number of (somewhat) flat-headed pachycephalosaurs (Homalocephale calathocercos, Goyocephale lattimorei, and Wannanosaurus yansiensis). However, prior to the discovery of Dracorex, the only semi-flat-headed pachycephalosaur from North America was Stegoceras validum (inclusive of Ornatotholus browni). Even then, the semi-flat-headed trait was only present in juveniles of the species.

Aside from having a flat, nodal skull, the most prominent feature of Dracorex is the pair of huge and unrestricted superior temporal openings. The supratemporal fenestrae are much larger front-to-back and side-to-side than in Homalocephale, and larger than in Goyocephale. Only a fragmentary Wannanosaurus skull shows fenestrae as large as those of Dracorex. This fenestral architecture has been seen in ancient archosaurs, but not in other pachycephalosaurs.

Consequently, if unreduced superior fenestrae are morphologically primitive, then Dracorex is more primitive in the temporal region than any other known pachycephalosaur. However, Sullivan (2003, 2006) demonstrated that the oldest known pachycephalosaurs were, in fact, fully-domed, and that the flat-headed morphology appeared later in the fossil record. This suggests that doming may be primitive for pachycephalosaurs and that a reversion to the non-domed, flat-headed state is a secondary (derived) character reversion, coupled with the re-opening of the supratemporal fenestrae. Indeed, while Stegoceras has been considered to be transitional between domed and flat-headed taxa, it may indicate the beginning of a character reversion to suppression of doming and opening of the supratemporal fenestrae in some taxa.

The excavated specimen was most likely a young adult. However, based on ossification of the mid-cervical arch with the centrum, it was near maturity. The animal was approximately 10 feet (3 m) long.

However, at the 2007 annual meeting of the Society of Vertebrate Paleontology, Jack Horner of Montana State University presented evidence, from analysis of the skull of holotype specimen TCMI 2004.17.1, that Dracorex may well be a juvenile form of Pachycephalosaurus.

Name
The name Dracorex hogwartsia was inspired by young visitors to the Children's Museum of Indianapolis as a tribute to both dragons (Dracorex means "dragon king"), which the animal resembled, as well as the Harry Potter series of books by J.K. Rowling (hogwartsia for the Hogwarts School of Witchcraft and Wizardry, the fictional school from the popular series).