Parasaurolophus

*Parasaurolophus walker*

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***Parasaurolophus*** (pronounced /ˌpærəsɔˈrɒləfəs/ PARR-ə-saw-ROL-ə-fəs, commonly also /ˌpærəˌsɔrəˈloʊfəs/ PARR-ə-SAWR-ə-LOH-fəs; meaning "near crested lizard" in reference to *Saurolophus*) is a genus of ornithopod dinosaur from the Late Cretaceous Period of what is now North America, about 76-73 million years ago. It was a herbivore that walked both as a biped and a quadruped. Three species are recognized: *P. walkeri* (the type species), *P. tubicen*, and the short-crested *P. cyrtocristatus*. Remains are known from Alberta, Canada, and New Mexico and Utah, USA. It was first described in 1922 by William Parks from a skull and partial skeleton in Alberta.

*Parasaurolophus* is a hadrosaurid, part of a diverse family of Cretaceous dinosaurs known for their range of bizarre head adornments. This genus is known for its large, elaborate cranial crest, which at its largest forms a long curved tube projecting upwards and back from the skull. *Charonosaurus* from China, which may have been its closest relative, had a similar skull and potentially a similar crest. The crest has been much discussed by scientists; the consensus is that major functions included visual recognition of both species and sex, acoustic resonance, and thermoregulation. It is one of the rarer duckbills, being known from only a handful of good specimens.

*Parasaurolophus* is among the most well-recognized dinosaurs, and is frequently portrayed in dinosaur-related television shows, movies, books, merchandise and other media.

## Description

As is the case with most dinosaurs, the skeleton of *Parasaurolophus* is incompletely known. The length of the type specimen of *P. walkeri* is estimated at 9.5 meters (31 ft). Its skull is about 1.6 meters (5.2 ft) long, including the crest, whereas the type skull of *P. tubicen* is over 2.0 meters (6.6 ft) long, indicating a larger animal. Its weight is estimated at 2.5 tonnes (2.7 tons). Its single known forelimb was relatively short for a hadrosaurid, with a short but wide shoulder blade. The thighbone measures 103 centimeters (3.38 ft) long in *P. walkeri* and is robust for its length when compared to other hadrosaurids. The upper arm and pelvic bones were also heavily built.

Like other hadrosaurids, it was able to walk on either two legs or four. It probably preferred to forage for food on four legs, but ran on two. The neural spines of the vertebrae were tall, as was common in lambeosaurines; tallest over the hips, they increased the height of the back. Skin impressions are known for *P. walkeri*, showing uniform tubercle-like scales but no larger structures.

The most noticeable feature was the cranial crest, which protruded from the rear of the head and was made up of the premaxilla and nasal bones. The *P. walkeri* type specimen has a notch in the neural spines near where the crest would hit the back, but this may be a pathology peculiar to this individual. William Parks, who named the genus, hypothesized that a ligament ran from the crest to the notch to support the head. Although the idea seems unlikely, *Parasaurolophus* is sometimes restored with a skin flap from the crest to the neck.

The crest was hollow, with distinct tubes leading from each nostril to the end of the crest before reversing direction and heading back down the crest and into the skull. The tubes were simplest in *P. walkeri*, and more complex in *P. tubicen*, where some tubes were blind and others met and separated. While *P. walkeri* and *P. tubicen* had long crests with only slight curvature, *P. cyrtocristatus* had a short crest with a more circular profile.

## Classification

As its name implies, *Parasaurolophus* was initially thought to be closely related to *Saurolophus* because of its superficially similar crest. However, it was soon reassessed as a member of the lambeosaurine subfamily of hadrosaurids—*Saurolophus* is an hadrosaurine. It is usually interpreted as a separate offshoot of the lambeosaurines, distinct from the helmet-crested *Corythosaurus*, *Hypacrosaurus*, and *Lambeosaurus*. Its closest known relative appears to be *Charonosaurus*, a lambeosaurine with a similar skull (but no complete crest yet) from the Amur region of northeastern China, and the two may form a clade Parasaurolophini. *P. cyrtocristatus*, with its short, rounder crest, may be the most basal of the three known *Parasaurolophus* species, or it may represent subadult or female specimens of *P. tubicen*.

## Paleobiology

### Cranial crest

Many hypotheses have been advanced as to what functions the cranial crest of *Parasaurolophus* performed, but most have been discredited. It is now believed that it may have had several functions: visual display for identifying species and sex, sound amplification for communication, and thermoregulation. It is not clear which was most significant at what times in the evolution of the crest and its internal nasal passages.

#### Differences between species and growth stages

As for other lambeosaurines, it is believed that the cranial crest of *Parasaurolophus* changed with age and was a sexually dimorphic characteristic in adults. James Hopson, one of the first researchers to describe lambeosaurine crests in terms of such distinctions, suggested that *P. cyrtocristatus*, with its small crest, was the female form of *P. tubicen*. Thomas Williamson suggested it was the juvenile form. Neither hypothesis became widely accepted. As only six good skulls and one juvenile braincase are known, additional material will help clear up these potential relationships. Williamson noted that in any case, juvenile *Parasaurolophus* probably had small, rounded crests like *P. cyrtocristatus*, that probably grew faster as individuals approached maturity. Recent restudy of a juvenile braincase previously assigned to *Lambeosaurus*, and now assigned to *Parasaurolophus*, provides evidence that a small tubular crest was present in juveniles. This specimen preserves a small upward flaring of the frontal bones that was similar to but smaller than what is seen in adult specimens; in adults, the frontals formed a platform that supported the base of the crest. This specimen also indicates that the growth of the crest in *Parasaurolophus* and the facial profile of juvenile individuals differed from the *Corythosaurus*-*Hypacrosaurus*-*Lambeosaurus* model, in part because the crest of *Parasaurolophus* lacks the thin bony 'coxcomb' that makes up the upper portion of the crest of the other three lambeosaurines.

## JPInstitute.com Description

Parasaurolophus was a very unique looking dinosaur. It had a very prominent crest atop its head that was almost six feet in length. This hollow tube was probably used to make sounds that may have allowed it to call to others in its herd. It was one of the largest plant-eaters of the Cretaceous Period.

Parasaurolophus would have walked primarily on all four legs, but it could have stood on its hind legs to feed or defend itself and used its long tail for balance. It had a fairly long neck that would have allowed it to find food on the ground or in trees. It was a member of family of dinosaurs we refer to as duckbills, meaning it had a hard beak in the front of its mouth and hundreds of teeth in the back for chewing tough plant material. These types of plant-eaters were most likely easy prey for the large predators of this time, so it probably found safety in numbers.

The long tube that makes up the crest is connected to the nostrils and the back of the throat of this dinosaur. It may have been able to make very loud sounds that could have been heard for miles.

## Links

http://web.archive.org/web/20040214161748fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_paras.html#

## References

1. ↑ Lull, Richard Swann Wright, Nelda E. *Hadrosaurian Dinosaurs of North America*, page 229. Published: 1942, Geological Society of America, *Geological Society of America Special Paper **40***
2. ↑ 2.0 2.1 2.2 Glut, Donald F. Dinosaurs: The Encyclopedia, Chapter: *Parasaurolophus*, pages 678–684. Published: 1997, McFarland & Co, in Jefferson, North Carolina. ISBN 0-89950-917-7
3. ↑ 3.0 3.1 3.2 Lull and Wright, *Hadrosaurian Dinosaurs of North America*, pp. 209-213.
4. ↑ Brett-Surman, Michael K. and Wagner, Jonathan R. Carpenter, Kenneth (ed.) *Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs*, chapter: *Appendicular anatomy in Campanian and Maastrichtian North American hadrosaurids*, pages 135–169. Published, 2006, Indiana University Press, in Bloomington and Indianapolis ISBN 0-253-34817-X
5. ↑ 5.0 5.1 Horner, John R., Weishampel, David B.; and Forster, Catherine A, Weishampel, David B.; Osmólska, Halszka; and Dodson, Peter (eds.) *The Dinosauria*, 2nd edition, chapter: Hadrosauridae, pages 438-463. Published: 2004, University of California Press, in Berkeley. ISBN 0-520-24209-2
6. ↑ 6.0 6.1 6.2 Parks, William A. *Parasaurolophus walkeri*, a new genus and species of crested trachodont dinosaur, volume 13, pages 1-32. Published: 1922, University of Toronto Studies, Geology Series.
7. ↑ Sullivan, Robert M. and Williamson, Thomas E. A new skull of *Parasaurolophus* (Dinosauria: Hadrosauridae) from the Kirtland Formation of New Mexico and a revision of the genus, from the series *New Mexico Museum of Natural History and Science Bulletin*, **15**, pages 1-52. Published: 1999, New Mexico Museum of Natural History and Science, in Albuqueque, New Mexico.
8. ↑ Ostrom, John H. 1961 *A new species of hadrosaurian dinosaur from the Cretaceous of New Mexico*, Journal of Paleontology, Volume 35, 3rd issue, on pages 575–577.
9. ↑ Gilmore, Charles W., On the genus *Stephanosaurus*, with a description of the type specimen of *Lambeosaurus lambei*, volume 38, issue 43, pages 29-48, Parks. Published: 1924, Canada Department of Mines Geological Survey Bulletin (Geological Series)
10. ↑ Weishampel, David B. and Horner, Jack R., Weishampel, David B.; Osmólska, Halszka; and Dodson, Peter (eds.) *The Dinosauria*, 1st edition, Chapter: Hadrosauridae, pages 534-561. Published: 1990, University of California Press in Berkeley. ISBN 0-520-06727-4
11. ↑ 11.0 11.1 11.2 Evans, David C., and Reisz, Robert R. 2007. Anatomy and relationships of *Lambeosaurus magnicristatus*, a crested hadrosaurid dinosaur (Ornithischia) from the Dinosaur Park Formation, Alberta, from the Journal of Vertebrate Paleontology, vol. 27 issue 2, on pages 373–393. [1]
12. ↑ Godefroit, Pascal, Shuqin Zan; and Liyong Jin. 2000. *Charonosaurus jiayinensis* n. g., n. sp., a lambeosaurine dinosaur from the Late Maastrichtian of northeastern China, from the Compte Rendus de l'Academie des Sciences, Paris, Sciences de la Terre et des planètes, vol. 330, pages 875–882.
13. ↑ 13.0 13.1 13.2 Williamson, Thomas E. 2000. Review of Hadrosauridae (Dinosauria, Ornithischia) from the San Juan Basin, New Mexico Lucas, S.G.; and Heckert, A.B. (eds.) Dinosaurs of New Mexico, from the New Mexico Museum of Natural History and Science Bulletin, **17** Published by New Mexico Museum of Natural History and Science, in Albuqueque, New Mexico. Pages 191–213.
14. ↑ Norman David B. *The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom*, chapter: Hadrosaurids II. 1985. Published by Crescent Books, in New York. Pages 122–127. ISBN 0-517-468905
15. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `DCE06`
16. ↑ Hopson, James A. 1975. *The evolution of cranial display structures in hadrosaurian dinosaurs* , from the Journal of Paleobiology, volume one, issue one, pages 21–43.
17. ↑ Evans, David C., Reisz, Robert R.; and Dupuis, Kevin, 2007. A juvenile *Parasaurolophus* braincase from Dinosaur Provincial Park, Alberta, with comments on crest ontogeny in the genus. Journal of Vertebrate Paleontology, vol. 27, issue 3 pages 642–650.