Pachycephalosaurus is an extinct genus of ornithschian dinosaurs. It was a bipedal herbivore with an extremely thick skull roof, long legs and short arms. It lived during the Late Cretaceous lived with other North American dinosaurs such as Triceratops and Tyrannosaurus. The fossil can be found in both the United States and Canada. It was an herbivorous or omnivorous creature which is primarily known from a single skull and a few extremely thick skull roofs, though more complete fossils have been found in recent years. Pachycephalosaurus was one of the last non-avian dinosaurs before the Cretaceous–Paleogene extinction event. Another dinosaur, Tylosteus of western North America, has been synonymized with Pachycephalosaurus.
Like other pachycephalosaurids, Pachycephalosaurus was a bipedal omnivore with an extremely thick skull roof. It possessed long hindlimbs and small forelimbs. Pachycephalosaurus is the largest known pachycephalosaur.
The thick skull domes of Pachycephalosaurus and related genera gave rise to the theory that pachycephalosaurs used their skulls to fight each other. This theory has been disputed in the past few years.
History[]
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Skull AMNH 1696
Remains attributed to Pachycephalosaurus may have been found since the 1850s. As judged by Donald Baird, in 1859 or 1860 Ferdinand Vandiveer Hayden, an early fossil collector in the North American West, picked up a piece of bone close to the head of the Missouri River, from what is now known to be the Lance Formation in Montana. [1] This specimen was described by Joseph Leidy in 1872 as from the dermal plate of a reptile or an armadillo-like animal. [2] Its true nature was not found until Baird restudied it a century later and identified it as a bone from the back of the skull of Pachycephalosaurus, including a set of bony knobs that matched those found on other specimens of Pachycephalosaurus. [3] Since the name Tylosteus predates Pachycephalosaurus, according to the International Code of Zoological Nomenclature it should be used. In 1985, Baird successfully petitioned to have Pachycephalosaurus used in lieu of the old Tylosteus as the latter name had not been used for more than 50 years, was based on undiagnostic materials, and had poor information. [4] [5] This may not be the end; Robert Sullivan suggested in 2006 that the fossil is more like the bone of Dracorex than that of Pachycephalosaurus.[6] The could be of little importance, though, if Dracorex is deemed a youn Pachycephalosaurus, as has been recently proposed. [7]
P. wyomingensis, the type and sole valid species of Pachycephalosaurus so far, was named by Charles W. Gilmore in 1931. He coined it for a skull from the Lance Formation of Niobrara County, Wyoming. Gilmore assigned his new species to Troodon as T. wyomingensis. [8]At the time, paleontologists thought that Troodon, then known just from teeth, was the same as Stegoceras, which had similar teeth. Therefore, what are now known as pachycephalosaurids were assigned to the family Troodontidae, a wrong idea not corrected until 1945, by Charles M. Sternberg. [9]
The holotype adult skull of P. "reinheimeri" (DMNS 469)
In 1943, Barnum Brown and Erich Maren Schlaikjer, with newer, more complete material, established the genus Pachycephalosaurus. They named two species: Pachycephalosaurus grangeri, the type species of the genus Pachycephalosaurus, and Pachycephalosaurus reinheimeri. P. grangeri was based on AMNH 1696, a nearly complete skull from the Hell Creek Formation of Ekalaka, Carter County, Montana. P. reinheimeri was based on what is now DMNS 469, a dome and a few associated elements from the Lance Formation of Corson County, South Dakota.
They also referred the older species "Troodon" wyomingensis to their new genus. Their two newer species have been considered synonymous with P. wyomingensis since 1983.
In 2015, some pachycephalosaurid material and a domed parietal attributable to Pachycephalosaurus were discovered in Scollard Formation, Alberta, Canada, implying dinosaurs of this era were cosmopolitan and didn't have discrete faunal provinces.
Description[]
Restoration
Size compared to a human
The anatomy of Pachycephalosaurus is not well known, as only its skull has been described. [10] Pachycephalosaurus is famed for its large dome on top of its skull, made of up to 10 in thick bone, which kept its tiny brain safe. The dome's rear aspect was edged with bony knobs and short bony spikes sticking up from the snout. The spikes were likely blunt, not sharp. These features suggest that, despite their bipedal stance, they were likely to have been relatives of the ceratopsians possibly branching from early individuals of the group.
Using data from other pachycephalosaurids, it has been estimated that Pachycephalosaurus was approximately the length of a large car, maybe around 4.6m long (15 feet) and had a fairly short, thick neck, short fore limbs, a bulky body, long hind legs and a heavy tail, which was likely to have been held rigid by ossified tendons. The skull was short, with large, rounded eyes that faced towards the front, suggesting that the animal had good sight and was capable of binocular vision. Pachycephalosaurus had a small snout which ended in a sharp beak. The teeth were tiny, with leaf-shaped crowns. The head was supported by an "S"- or "U"-shaped neck. [11]
Pachycephalosaurus was likely bipedal and was the largest in the group family. It measured 15 to 16 feet long, stood 6 feet tall which is the same height as Deinonychus, and weighed 990 pounds.[12] Based on other dome-headed dinosaurs, it probably had a short, thick neck, short fore limbs, a strong body, long hind legs and a thick tail, which was likely held stiff by ossified tendons. [13]
Lifestyle[]
Scientists once suspected that Pachycephalosaurus and its dome-headed relatives were the bipedal equivalents of the big-horned sheep of today. It was thought that, in the mating season, big males would run at one another, clashing heads to decide which would dominate and mate with a herd of females. It was also thought that they might have used their domed heads for defense against predators. However, it is now believed that the Pachycephalosaurs would not have used their domes in this way so much.
The adult head bones could not adequately have withstood pressure and impact and the skulls lacked proper shock absorption like Big Horned Sheep, and it's more likely that they head-butted their sides, to try to knock them off balance. Also, there is no evidence of scars or other damage on fossilized Pachycephalosaurus skulls possibly caused by head-butting. On the other hand, it's unlikely that pachycephalosaurs developed those thick skulls for display alone. It's a rather opinionated discussion.
Scientists do not yet know what these dinosaurs ate. Having very small, ridged teeth they could not have chewed tough, fibrous plants as effectively as other dinosaurs of the same period. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, fruit and insects. The sharp, serrated teeth would have been very effective for shredding plants such as ferns. The diet of insects is a debatable one however, some say that Pachycephalosaurus was a true carnivore, while some explain how this animal might've been a well omnivore.
Habitats[]
It is believe that Pachycephalosaurus lived in woods, forests, feilds, meadows, lowlands, grasslands and plains of Montana, North Dakota, South Dakota, Wyoming and Alberta during the Late Cretaceous and little bit in the Early Paleogene. The dinosaurs it shared these locations with can be found in many of the same locations that Pachycephalosaurus inhabited. The floodplains that Pachycephalosaurus lived in had trees, grass, shrubs, ferns, woodlands, ponds, streams, rivers, brooks, creeks and valleys.
Lance Formation[]
Was a plain filled with streams forest and woods the formation was named after Lance Creek and located in Wyoming. The Lance Formation was one of the many places that Pachycephalosaurus called home. The area had plains with trees, meadows, swamps, steams, creeks, brooks, ponds, ferns, shrubs and wooded areas but it was mostly believed to be a wetland floodplain. Pachycephalosaurus not only lived alongside dinosaurs in the Lace Formation but it shared the area with birds, reptiles like lizards, crocodiles, alligators, snakes, turtles, alongside amphibians like, frogs, salamanders and toads, also invertebrates like, arachnids, insects, arthropods, crustaceans, fish and small mammals. Pachycephalosaurus individuals have been found elsewhere other than Lance Formation.
Scollard Formation[]
Was a plain located near Scollard Canyon the formation is named after the canyon in Alberta, Canada. Scollard Formation was one of the many places that Pachycephalosaurus made it's home like other habitats that the dinosaur lived in this location was believed to be a floodplain at one point with forests, meadows, fields, brooks, ponds, creeks, ferns, grass, trees, shrubs and woods located in the plains. Pachycephalosaurus has also been found alongside next to the Scollard Canyon. Animals like, birds, fish, amphibians like, frogs, toads, salamanders, birds, reptiles like, snakes, lizards, turtles, alligators, crocodiles, invertebrates like, insects, arachnids, crustaceans, arthropods, and small mammals lived in plains of Scollard at the sametime with Pachycephalosaurus and other dinosaurs.
Classification[]
Casts of three skulls, representing possible growth stages, Museum of the Rockies
Pachycephalosaurus gives its name to the Pachycephalosauria, a clade of herbivorous ornithischian ("bird hipped") dinosaurs which lived during the Late Cretaceous Period in North America and Asia. Despite their bipedal stance, they were likely more closely related to the ceratopsians than the ornithopods.
Pachycephalosaurus is the most famous member of the Pachycephalosauria (though not the best-preserved member). The clade also includes Stenopelix, Wannanosaurus, Goyocephale, Stegoceras, Homalocephale, Tylocephale, Sphaerotholus and Prenocephale. Within the tribe Pachycephalosaurini, Pachycephalosaurus is most closely related to Alaskacephale. Dracorex and Stygimoloch have been synonymized with Pachycephalosaurus. Debates and arguments of how Dracorex or Stygimoloch may have been a juvenile of Pachycephalosaurus are still ongoing.
Below is a cladogram modified from Evans et al., 2013.
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Paleobiology[]
Presentable depiction of Pachycephalosaurus
Growth[]
Growth series showing reduction of spikes and growth of dome with age, according to Horner and Goodwin
The pachycephalosaur Dracorex may actually be a Stygimoloch or Pachycephalosaurus in which the dome and horns are not well-developed, either because the animal was a juvenile or a female. This idea was backed up at the 2007 annual meeting of the Society of Vertebrate Paleontology.[14] Jack Horner of Montana State University showed proof, from study of the skull of the one existing Dracorex specimen, that this dinosaur may well be a young form of Stygimoloch. Plus, he showed data that shows both Stygimoloch and Dracorex may be young forms of Pachycephalosaurus. Horner and M.B. Goodwin published their findings in 2009, that showed the spike/node and skull dome bones of all three 'species' have extreme plasticity, and that both Dracorex and Stygimoloch are just known from young specimens while Pachycephalosaurus is just known from adult specimens. These notes, as well as the fact that all three forms lived in the same time and place, lead them to think that Dracorex and Stygimoloch were just young Pachycephalosaurus, which lost spikes and grew domes as they aged.[15] A 2010 study by Nick Longrich and colleagues also backed up the theory that all flat-skulled pachycephalosaurs were young, suggesting that flat-skulled forms like Goyocephale and Homalocephale represent juveniles of dome-skulled adults.[16]
Size of an adult P. wyomingensis (green) and potential growth stages, compared to a human
The discovery of baby skulls assigned to Pachycephalosaurus that were described in 2016 from two different bone beds in the Hell Creek Formation has been presented as further evidence for this hypothesis. The fossils, as described by David Evans and Mark Goodwin et al are identical to all three supposed genera in the placement of the rugose knobs on their skulls, and the unique features of Stygimoloch and Dracorex are thus instead morphologically consistent features on a Pachycephalosaurus growth curve.
Dome function[]
Paleoart of head-butting subadults
It has been commonly hypothesized that Pachycephalosaurus and its relatives were the bipedal equivalents of bighorn sheep or musk oxen, where male individuals would ram each other headlong, and that they would horizontally straighten their head, neck, and body in order to transmit stress during ramming. However, there have also been alternative suggestions that the pachycephalosaurs could not have used their domes in this way.
The primary argument that has been raised against head-butting is that the skull roof may not have adequately sustained impact associated with ramming, as well as a lack of definitive evidence of scars or other damage on fossilized Pachycephalosaurus skulls (however, more recent analyses have uncovered such damage; see below).[17] Furthermore, the cervical and anterior dorsal vertebrae show that the neck was carried in an "S"- or "U"-shaped curve, rather than a straight orientation, and thus unfit for transmitting stress from direct head-butting. Lastly, the rounded shape of the skull would lessen the contacted surface area during head-butting, resulting in glancing blows.
Depressions on the skull of specimen BMRP 2001.4.1
It is more likely that the Pachycephalosaurus and other pachycephalosaurs hit each other in the flanks. In this setting, an individual may have stood parallel or faced a rival directly, using intimidation displays to rival. If intimidation failed, the Pachycephalosaurus would bend its head down and to the side, and strike the rival pachycephalosaur on its flank. This hypothesis is back up by the broad width of most pachycephalosaurs, a trait that would have kept vital organs from harm. The flank-butting theory was first proposed by Sues in 1978, and expanded by Ken Carpenter in 1997.[18]
Restoration of a specimen with a cranial lesion
In 2012, a study showed that cranial pathologies in a P. wyomingensis specimen were likely due to agonistic behavior. It was also proposed that similar damage in other pachycephalosaur specimens previously explained as taphonomic artifacts and bone absorptions may instead have been due to such behavior. Peterson et al. (2013) studied cranial pathologies among the Pachycephalosauridae and found that 22% of all domes examined had lesions that are consistent with osteomyelitis, an infection of the bone resulting from penetrating trauma, or trauma to the tissue overlying the skull leading to an infection of the bone tissue. This high rate of pathology lends more support to the hypothesis that pachycephalosaurid domes were employed in intra-specific combat.
Pachycephalosaurus wyomingensis specimen BMR P2001.4.5 was observed to have 23 lesions in its frontal bone and P. wyomingensis specimen DMNS 469 was observed to have 5 lesions. The frequency of trauma was comparable across the different genera in the pachycephalosaurid family, despite the fact that these genera vary with respect to the size and architecture of their domes, and fact that they existed during varying geologic periods. These findings were in stark contrast with the results from analysis of the relatively flat-headed pachycephalosaurids, where there was an absence of pathology. This would support the hypothesis that these individuals represent either females or juveniles, where intra-specific combat behavior is not expected.
Histological examination reveals that pachycephalosaurid domes are composed of a unique form of fibrolamellar bone which contains fibroblasts that play a critical role in wound healing, and are capable of rapidly depositing bone during remodeling. Peterson et al. (2013) concluded that taken together, the frequency of lesion distribution and the bone structure of frontoparietal domes, lends strong support to the hypothesis that pachycephalosaurids used their unique cranial structures for agonistic behavior. CT scan comparisons of the skulls of Stegoceras validum, Prenocephale prenes, and several head-striking artiodactyls have also supported pachycephalosaurids as being well-equipped for head-butting. New studies reveal that Pachycephalosaurus and other Pachycephalosaurids may have actually rammed the sides of each other instead, rather than going head-on.
Diet[]
Scientists do not yet know what these dinosaurs ate. Having small, ridged teeth they could not have chewed tough, fibrous plants as effectively as other dinosaurs of the same time. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, fruit and insects. The sharp, jagged teeth would have been very effective for shredding plants.[19] It is also suspected that the dinosaur may have included meat in its diet. The most complete fossil jaw shows that it had serrated blade-like front teeth, reminiscent of those of carnivorous theropods. For now, it's safe to assume that the Pachycephalosaurus likely ate assorted plants like moss, ferns, seeds, and fruits. There are discussions about this particular dinosaur could potentially be Omnivorous.
Paleoecology[]
Pachycephalosaurus and other animals of the Hell Creek Formation
Nearly all Pachycephalosaurus fossils have been recovered from the Lance Formation and Hell Creek Formation of the western United States.[20] Pachycephalosaurus possibly coexisted alongside additional pachycephalosaur species of the genera Sphaerotholus, as well as Dracorex and Stygimoloch, though these last two genera may represent juveniles of Pachycephalosaurus itself. [21] Other dinosaurs that shared its time and place include Thescelosaurus, the hadrosaurid Edmontosaurus and a possible species of Parasaurolophus, ceratopsids like Triceratops, Torosaurus, and Leptoceratops, ankylosaurid Ankylosaurus, nodosaurids Denversaurus and Edmontonia, and the theropods Acheroraptor, Dakotaraptor, Ornithomimus, Struthiomimus, Anzu, Leptorhynchos, Pectinodon, Paronychodon, Richardoestesia, and Tyrannosaurus. shared its time and place.[22]
JPInstitute.com Description[]
This was a real bonehead. The skull of Pachycephalosaurus was 10 inches thick on top. For years, scientists thought it was used primarily for head-butting contests, sort of like mountain goats do today, but recent studies of the skeletons of related dinosaurs show that its neck might have broken if it tried that.
A skeleton of the Pachycephalosaurus has never been found, so most of what is known about it is only from the skull and its close relatives. There are several strange characteristics, in addition to its thick skull. It lived at the very end of the dinosaur age, when most dinosaurs were fairly advanced, yet it still had five fingers, a primitive characteristic. Also, the shape of its teeth was somewhat primitive, similar to those of the Stegosaurus which had lived over 100 million years earlier. These were clearly plant-eater teeth, but it also had front teeth that could have been used like a meat-eater.
Dinosaur Field Guide Description[]
Pachycephalosaurus (Thick-headed lizard") is the last and most famous member of the Pachycephalosauria, or thick-headed dinosaurs. In the 1970s, paleontologist Peter Galton proposed that male pachycephalosaurs used their domed heads as battering rams, like bighorn sheep. The idea caught the public's imagination. In The Lost World: Jurassic Park, you can even see the dome-headed pachycephalosaurs doing head butts (of course, these are genetically engineered dinosaurs and not necessarily the exact same ones that lived 70 million years ago!). But by the 1990s, scientists began to question Galton's head-butting theory. It was pointed out that animals who do butt heads have a wide surface area where the heads come into contact to prevent "head slippage." This happens when two animals butt heads at high speed and do not hit straight on. They risk breaking their necks when their heads suddenly snap to one side. Pachycephalosaurus has a domed, or rounded, head, which would minimize surface contact and therefore increase the risk of head slippage. This throws doubt on the idea of any high-speed head-butting between pachycephalosaurs, but it does not exclude "head-pushing" or "head-ramming" against non-pachycephalosaurs. It just happens that if a pachycephalosaur lowered its head and charged at a theropod, the impact would be right at the level of the theropod's head or pelvis- the perfect place to stop an attacker. Since Pachycephalosaurus had a skull up to 9 inches (23 cm) thick, guess who'd lose?
Fun Facts[]
Males had larger and more ornamented bumps on the back of their skulls than females.
Trivia[]
The teeth of Pachycephalosaurus are smaller than the first teeth of a human baby!
Gallery[]
Appearance in other media[]
Jurassic Park[]
- Pachycephalosaurus appeared in the 1997 film The Lost World: Jurassic Park stampeding with the other dinosaurs. One of them appeared in the 2015 film Jurassic World & was tranquilized to sleep after escaping it's enclosure. It has been revealed that there are surviving populations of Pachycephalosaurus on Isla Nublar, but none were seen being evacuated from the island aboard the S.S Arcadia in the 2018 film, Jurassic World: Fallen Kingdom but its sound was heard when the poison gas is leaking before all the dinosaurs escape into the mainland. In the 2022 film, Jurassic World: Dominion, it was theorized that the Pachycephalosaurus as well as other Jurassic Park originals may make a debut themselves.
- Pachycephalosaurus was featured in the Vivendi Universal video game Jurassic Park: Operation Genesis.
- Pachycephalosaurus appeared in Jurassic World: Evolution. It seems to be based on the Lost World design.
- Pachycephalosaurus makes an appearance in the mobile game, Jurassic World: Alive as an Epic Resilient creature. It can be fused to create the Smilocephalosaurus, hybrid of the Pachycephalosaurus and the Smilodon.
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Read more Pachycephalosaurus on Jurassic Park Wiki |
The Land Before Time[]
- Pachycephalosaurus had some roles in the Land Before Time franchise, where they are depicted as secondary villains. A trio of Pachycephalosaurus (possibly the males) charging Cera in The Land Before Time, but they make their return in The Land Before Time IV: Journey Through the Mists when a pair of them fight each other and Petrie gets dizzy to see them fighting. However in the later movies they were one of the dinosaurs living in the Great Valley (possibly the females).
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Read more Pachycephalosaurus on Land Before Time Wiki |
We're Back! A Dinosaur's Story[]
- A Pachycephalosaurus named Chrome-Dome appears in Your Pet Dinosaur: An Owner's Manual
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Read more Pachycephalosaurus on We’re Back A Dinosaur’s Story Wiki |
Links[]
References[]
- ↑ Baird, Donald (1979). "The dome-headed dinosaur Tylosteus ornatus Leidy 1872 (Reptilia: Ornithischia: Pachycephalosauridae)". Notulae Naturae 456: 1–11.
- ↑ Leidy, Joseph (1872). "Remarks on some extinct vertebrates". Proceedings of the Academy of Natural Sciences of Philadelphia, 1872: 38–40.
- ↑ Baird, Donald (1979). "The dome-headed dinosaur Tylosteus ornatus Leidy 1872 (Reptilia: Ornithischia: Pachycephalosauridae)". Notulae Naturae 456: 1–11.
- ↑ ICZN Opinion 1371, "Pachycephalosaurus Brown & Schlaikjer, 1943 and Troodon wyomingensis Gilmore, 1931 (Reptilia, Dinosauria): Conserved." Bulletin of Zoological Nomenclature, 43 (1): April 1986.
- ↑ Glut, Donald F. (1997). "Pachycephalosaurus". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. pp. 664–668. ISBN 0-89950-917-7.
- ↑ Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)". Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366. Retrieved 2010-11-10.
- ↑ Stokstad, Erik (2007). "SOCIETY OF VERTEBRATE PALEONTOLOGY MEETING: Did Horny Young Dinosaurs Cause Illusion of Separate Species?". Science 318 (5854): 1236. doi:10.1126/science.318.5854.1236. PMID 18033861.
- ↑ Gilmore, Charles W. (1931). "A new species of troodont dinosaur from the Lance Formation of Wyoming". Proceedings of the United States National Museum 79 (9): 1–6.
- ↑ Glut, Donald F. (1997). "Troodon". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. pp. 933–938. ISBN 0-89950-917-7.
- ↑ Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)". Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366. Retrieved 2010-11-10.
- ↑ Carpenter, Kenneth (1 December 1997). "Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior" (pdf). Contributions to Geology 32 (1): 19–25.
- ↑ Paul, Gregory S. (2010). The Princeton Field Guide to Dinosaurs. Princeton, NJ: Princeton University Press. p. 244. ISBN 978-0-691-13720-9.
- ↑ Organ, Christopher O.; Adams, Jason (2005). "The histology of ossified tendon in dinosaurs". Journal of Vertebrate Paleontology 25 (3): 602–613. doi:10.1671/0272-4634(2005)025[0602:THOOTI2.0.CO;2]. Retrieved 2008-06-10.
- ↑ 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
- ↑ Horner J.R. and Goodwin, M.B. (2009). "Extreme cranial ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus." PLoS ONE, 4(10): e7626. Online full text
- ↑ Longrich, N.R., Sankey, J. and Tanke, D. (2010). "Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA." Cretaceous Research, . doi:10.1016/j.cretres.2009.12.002
- ↑ Template:Cite journal
- ↑ Carpenter, Kenneth (1 December 1997). "Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior" (pdf). Contributions to Geology 32 (1): 19–25.
- ↑ Template:Cite book
- ↑ Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)". Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366. Retrieved 2010-11-10.
- ↑ Template:Cite journal
- ↑ Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loeuff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth, M.P.; and Noto, Christopher R. (2004). "Dinosaur Distribution". In: D.B. Weishampel, P. Dodson, and H. Osmólska (eds.) The Dinosauria (2nd edition). 517–606. ISBN 0-520-24209-2.