Fossil range: Late Cretaceous
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.
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 compara
ble to Stygimoloch. In the Pachycephalosauridae family, the Asian taxa includes a number of (somewhat) flat-headed pachycephalosaurs (Homalocephale calat'hocercos, 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 Ornatoth
olus' 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. 
In the original description, Bob Bakker included Dracorex in the family Pachycephalosauridae within the subfamily Pachycephalosaurinae. In the latter in the Pachycephalosaurini tribe together with Pachycephalosaurus forming a clearing next to Stygimoloch . To carry out the analysis of the relationships between the genders, he observed the differences in cranial ornamentation. 1
In a comprehensive study of numerous fossils of Pachycephalosaurus published in 2009, John R. Horner and Mark B. Goodwin , a strong variation warn ontogenetic of the skull : large morphological differences between juveniles and adults. For them, the flat Dracorex skull , the nodules at the front end, the small spines at the back, and the thick but non-dome-shaped frontoparietal, indicate that the only known specimen is a juvenile Pachycephalosaurus
wyomingensis . 6
Alternative interpretation 
Dracorex may be a closely related individual of Stygimoloch and / or Pachycephalosaurus in which the cupola and horns are not well developed either because the animal was a juvenile or a female. This consideration was supported at the 2007 annual meeting of the Society of Vertebrate Paleontology. 7 Jack Horner from Montana State University presented evidence, from analysis of the skull of the only extant specimen of Dracorex , that this dinosaur could be a juvenile form of Stygimoloch . In addition, he presented data indicating that both Stygimoloch and Dracorex may be juvenile forms ofPachycephalosaurus . Horner and MB Goodwin published their findings in 2009, showing that the spine / nodule bones and cranial domes of all three species' exhibit extreme plasticity and that both Dracorex and Stygimoloch are known only from juvenile specimens, while Pachycephalosaurus is only known from specimens. Adults". These observations, plus the fact that all three forms lived at the same time and place, lead them to conclude that Dracorex and Stygimoloch may have simply been juvenile Pachycephalosaurs that had lost their spines and developed domes as they aged. 6The researchers were unable to break out Dracorex's skull to sample it, 6 and had to use a cast of the skull for descriptive purposes. 6 A 2010 study by Nick Longrich and colleagues also supported the hypothesis that all flat-headed pachycephalosaurus were juveniles, suggesting that flat-domed forms, such as Goyocephale and Homalocephale , represent the juveniles of domed adults. 8 In 2016, Goodwin and Evans analyzed the youngest known ontogimorphs of Pachycephalosaurus , collected from the Hell Creek Formation. While this material would normally refer to DracorexSince it represented one or more individuals younger than the only known Dracorex individual and displayed similar characteristics, the items showed that the unique characters in Dracorex and Stygimoloch represent morphological characters consisting of a morphological continuum for Pachycephalosaurus . In other words, these younger individuals showed that Dracorex characteristics were probably transient and can be easily traced on a growth curve to Pachycephalosaurus , where Stygimoloch and Dracorex are incorporated into this genus. As such, DracorexIt is probably not a single species, but a more modern synonym for Pachycephalosaurus . 9 This study has not been challenging and represents the most recent analysis of this genre. In conclusion, an ontogenetic relationship is established, being infantile, juvenile and adult individuals of the same species, between Dracorex hogwartsia , Stygimoloch spinifer and Pachycephalosaurus wyomingensis , the latter being the bearer of the valid species name, as it is the first of the three to be described. 6 October
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).
- ^ Bakker, R. T., Sullivan, R. M., Porter, V., Larson, P. and Saulsbury, S.J. (2006). "Dracorex hogwartsia, n. gen., n. sp., a spiked, flat-headed pachycephalosaurid dinosaur from the Upper Cretaceous Hell Creek Formation of South Dakota." in Lucas, S. G. and Sullivan, R. M., eds., Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35, pp. 331–345. 
- ^ Erik Stokstad,"SOCIETY OF VERTEBRATE PALEONTOLOGY MEETING:Did Horny Young Dinosaurs Cause Illusion of Separate Species?", Science Vol. 18, 23 Nov. 2007, p. 1236; http://www.sciencemag.org/cgi/content/full/318/5854/1236.