Dracorex
Encyclopedia
Dracorex is a dinosaur
genus
of the family Pachycephalosauridae, from 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. However, Jack Horner et al. suspect that it is a juvenile Pachycephalosaurus
. Now, a new analysis of pachycephalosaur fossils by a joint team from the University of California, Berkeley and the Museum of the Rockies has questioned the validity of two named genera of pachycephalosaur, Dracorex and Stygimoloch.
According to the team, specimens of Dracorex and Stygimoloch might actually represent earlier growth stages of Pachycephalosaurus. As this article on the UC Berkeley website says, "The confusion is traced to their bizarre head ornaments, ranging from shields and domes to horns and spikes, which changed dramatically with age and sexual maturity, making the heads of youngsters look very different from those of adults."
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, the Asia
n 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 the beginning of ossification
of the mid-cervical arch with the centrum
, it was near maturity. The animal was approximately 10 feet (3 m) long.
and/or Pachycephalosaurus
in which the dome 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. Jack Horner of Montana State University
presented evidence, from analysis of the skull of the single existing Dracorex specimen, that this dinosaur may well be a juvenile form of Stygimoloch. In addition, he presented data that indicates that both Stygimoloch and Dracorex may be juvenile forms of Pachycephalosaurus. Horner and M.B. Goodwin published their findings in 2009, showing that the spike/node and skull dome bones of all three 'species' exhibit extreme plasticity, and that both Dracorex and Stygimoloch are known only from juvenile specimens while Pachycephalosaurus is known only from adult specimens. These observations, in addition to the fact that all three forms lived in the same time and place, lead them to conclude that Dracorex and Stygimoloch may have simply been juvenile Pachycephalosaurus, which lost spikes and grew domes as they aged. The researchers were unable to destructively sample the Dracorex skull, and had to use a cast of the skull for descriptive purposes. A 2010 study by Nick Longrich and colleagues also supported the hypothesis that all flat-skulled pachycephalosaurs were juveniles, suggesting that flat-skulled forms like Goyocephale and Homalocephale represent juveniles of dome-skulled adults.
series of books by J.K. Rowling (hogwartsia for the Hogwarts School of Witchcraft and Wizardry, the fictional school from the popular series).
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of the family Pachycephalosauridae, from the Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
of North America.
The type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
(and only) species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
is Dracorex hogwartsia, meaning "dragon
Dragon
A dragon is a legendary creature, typically with serpentine or reptilian traits, that feature in the myths of many cultures. There are two distinct cultural traditions of dragons: the European dragon, derived from European folk traditions and ultimately related to Greek and Middle Eastern...
king of Hogwarts
Hogwarts
Hogwarts School of Witchcraft and Wizardry or simply Hogwarts is the primary setting for the first six books of the Harry Potter series by J. K. Rowling, with each book lasting the equivalent of one school year. It is a fictional boarding school of magic for witches and wizards between the ages of...
". It is known from one nearly complete skull (the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as 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
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
in South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
by three amateur paleontologists from Sioux City
Sioux City, Iowa
Sioux City is a city in Plymouth and Woodbury counties in the western part of the U.S. state of Iowa. The population was 82,684 in the 2010 census, a decline from 85,013 in the 2000 census, which makes it currently the fourth largest city in the state....
, Iowa
Iowa
Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...
. 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. However, Jack Horner et al. suspect that it is a juvenile Pachycephalosaurus
Pachycephalosaurus
Pachycephalosaurus is a genus of pachycephalosaurid dinosaur. It lived during the Late Cretaceous Period of what is now North America. Remains have been excavated in Montana, South Dakota, and Wyoming. It was an herbivorous or omnivorous creature which is only known from a single skull and a few...
. Now, a new analysis of pachycephalosaur fossils by a joint team from the University of California, Berkeley and the Museum of the Rockies has questioned the validity of two named genera of pachycephalosaur, Dracorex and Stygimoloch.
According to the team, specimens of Dracorex and Stygimoloch might actually represent earlier growth stages of Pachycephalosaurus. As this article on the UC Berkeley website says, "The confusion is traced to their bizarre head ornaments, ranging from shields and domes to horns and spikes, which changed dramatically with age and sexual maturity, making the heads of youngsters look very different from those of adults."
Description
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
, 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
Stygimoloch
Stygimoloch is a putative genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 65 million years ago...
.
In the Pachycephalosauridae, the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n taxa includes a number of (somewhat) flat-headed pachycephalosaurs (Homalocephale calathocercos
Homalocephale
Homalocephale is a genus of dinosaur belonging to the pachycephalosaurid family, which lived during the late Cretaceous period of what is now Mongolia, 80 million years ago. The genus was described in 1974 by Osmólska & Maryañska, and consists of a single species, H...
, Goyocephale lattimorei
Goyocephale
Goyocephale is a genus of pachycephalosaurid dinosaur which lived during the Late Cretaceous period. It lived in what is now Mongolia.Goyocephale probably weighed 10–40 kg. The type species, Goyocephale lattimorei, was formally described by Perle, Maryañska, and Osmólka from an incomplete...
, and Wannanosaurus yansiensis
Wannanosaurus
Wannanosaurus is a genus of basal pachycephalosaurian dinosaur from the Campanian-age Upper Cretaceous Xiaoyan Formation, about 80 million years ago in what is now Anhui, China...
). However, prior to the discovery of Dracorex, the only semi-flat-headed pachycephalosaur from North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
was Stegoceras validum
Stegoceras
Stegoceras is a genus of plant-eating pachycephalosaurid dinosaur that lived in what is now North America during the Late Cretaceous period....
(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
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
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
Reversion
Reversion may refer to:*Reversion *Reversion *Reversion *Reversion *Series reversion, in mathematics*Reversion, in evolutionary biology...
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 the beginning of ossification
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
of the mid-cervical arch with the centrum
Body of vertebra
The body is the largest part of a vertebra, and is more or less cylindrical in shape. For vertebrates other than humans, this structure is usually called a centrum....
, it was near maturity. The animal was approximately 10 feet (3 m) long.
Classification
Dracorex may actually be an individual of the closely related StygimolochStygimoloch
Stygimoloch is a putative genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 65 million years ago...
and/or Pachycephalosaurus
Pachycephalosaurus
Pachycephalosaurus is a genus of pachycephalosaurid dinosaur. It lived during the Late Cretaceous Period of what is now North America. Remains have been excavated in Montana, South Dakota, and Wyoming. It was an herbivorous or omnivorous creature which is only known from a single skull and a few...
in which the dome 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. Jack Horner of Montana State University
Montana State University - Bozeman
Montana State University – Bozeman is a public university located in Bozeman, Montana. It is the state's land-grant university and primary campus in the Montana State University System, which is part of the Montana University System...
presented evidence, from analysis of the skull of the single existing Dracorex specimen, that this dinosaur may well be a juvenile form of Stygimoloch. In addition, he presented data that indicates that both Stygimoloch and Dracorex may be juvenile forms of Pachycephalosaurus. Horner and M.B. Goodwin published their findings in 2009, showing that the spike/node and skull dome bones of all three 'species' exhibit extreme plasticity, and that both Dracorex and Stygimoloch are known only from juvenile specimens while Pachycephalosaurus is known only from adult specimens. These observations, in addition to the fact that all three forms lived in the same time and place, lead them to conclude that Dracorex and Stygimoloch may have simply been juvenile Pachycephalosaurus, which lost spikes and grew domes as they aged. The researchers were unable to destructively sample the Dracorex skull, and had to use a cast of the skull for descriptive purposes. A 2010 study by Nick Longrich and colleagues also supported the hypothesis that all flat-skulled pachycephalosaurs were juveniles, suggesting that flat-skulled forms like Goyocephale and Homalocephale represent juveniles of dome-skulled adults.
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 PotterHarry Potter
Harry Potter is a series of seven fantasy novels written by the British author J. K. Rowling. The books chronicle the adventures of the adolescent wizard Harry Potter and his best friends Ron Weasley and Hermione Granger, all of whom are students at Hogwarts School of Witchcraft and Wizardry...
series of books by J.K. Rowling (hogwartsia for the Hogwarts School of Witchcraft and Wizardry, the fictional school from the popular series).
External links
- TEDx talk by Jack Horner on shape-shifting dinosaur skulls and dinosaur misclassification.