Parasaurolophus

Parasaurolophus is an ornithopod dinosaur genus. It lived in North America during the late Cretaceous (76.5-73 mya). The name Parasaurolophus means "near crested lizard". It belonged to the hadrosaurids, a diverse dinosaur family which thrieved during the Cretaceous Period, having quite spectacular ornaments on the top or back-top of their head. Parasaurolophus had a large and elaborate cranial crest, which curvely projected upwards and back from the head. Parasaurolophus belongs to the rarest hadrosaurids, known only from a small number of fossil remnants. As its name shows, Parasaurolophus was initially considered to be a very close relative of Saurolophus, but it turned out subsequently that they belong to two separate subfamilies within Hadrosauridae - Saurolophus belongs to Hadrosaurinae, while Parasaurolophus is a member of Lambeosaurinae.

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Known occurrences of Parasaurolophus fossils.

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Parasaurolophus walkeri. By Leandra Walters, Phil Senter, James H. Robins - http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144036, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=46753733

Valid species

There are three valid, well distinguishable species of the genus: the type species, P. walkeri; P. tubicen, and a short-crested species, P. cyrtocristatus. Moreover, P. jiayinensis was described as a fourth species, but it was placed in a separate genus, called Charonosaurus.

The genus was described by William Parks in 1922, based on a skull and an incomplete fossil skeleton in 1922. Fossils were found in Alberta (Canada), in New Mexico and Utah (United States). The first specimen was found in Canada, near Sand Creek in Alberta. The rocks from where it originates are known as the Dinosaur Park Formation, from the Upper Cretaceous. The type species Parasaurolophus walkeri was named after Sir Byron Edmund Walker, who was the Chairman of the Board of Trustees of the Royal Ontario Museum. The skeleton of the type specimen was not complete - it had its skull, but most of the tail was missing, and the hind legs below the knees[1]. In 1921, a new, partial skull was explored by Charles H. Sternberg in the Kirtland Formation, in San Juan City, New Mexico. This fossil gave the basis of the description of P. tubicen, described by Carl Wiman in 1931[2]. Its species name was derived from the the Latin "tubicěn" word, which means "trumpeter". In 1995 a nerly complete, second skull of P. tubicen was found in New Mexico. The third species, P. cyrtocristatus was described by John Ostrom in 1961, also from New Mexico. The exact finding location of the specimen is not known, but probably it was either the Fruitland Formation, or the Kirtland Formation. Its skull was not complete, but it had a short, rounded crest, furthermore, the skeleton lacked the feet, neck, and parts of the tail[3]. The specific names are made of the Latin words "curtus" (meaning "shortened") and "cristatus" (meaning "crested"). A partial skull of an other fossilized P. cyrtocristatus specimen was found by David B. Weishampel and James A. Jensen in the Kaiparowits Formation, Utah, in 1979[4]. Parasaurolophus walkeri can de differentiated from the other two species by having a simpler internal structure than P. tubicen, and by having a differnt internal structure and a straighter crest than in case of P. cyrtocristatus. Amongst the three species, P. tubicen was the largest, and P. cyrtocristatus the smallest one. Furthermore, P. cyrtocristatus has the most curved crest[5]. Some researchers suggested that P. cyrtocristatus was probably the female of P. walkeri or P. tubicen[6][7], however, other data, e.g. the approximately one million year difference between their age, the difference in distribution and in the internal structure of the crest, does not support this theory[8][9]. However, as only a few skulls belonging to this dinosaur genus are known, further material may help to elucidate these potential connections in the future.

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Parasaurolophus walkeri. By I, Steveoc 86, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1985435

Description and anatomy

Parasaurolophus could also walk in bipedal and in quadrupedal modes. The length of P. walkeri could be abut 9.5 meters, and the animal could weight about 2.5 tonnes[10], and its skull with the crest could be approximately 1.6 meters long, whereas the skull of P. tubicen, including the crest, was 2 meters long. The crest of all Parasaurolophus species was hollow, and the nostrils were connected by tubes with the end of the crest, then these tubes reversed and headed back down the crest, and into the skull. Parasaurolophus walkeri had the simplest crest, while that of P. tubicen was more comlex. The crest of P. cyrtocristatus was shorter and more circular[11]. The type specimen of P. walkeri probably has a paleopathological trait, i.e. it has a v-shaped gap in its vertebrae, near the base of the neck. Earlier it was thought that the top of the crest could be fitted into this gap, giving a strong support to the head[1]. However, a subsequent analysis suggests that this pathology was probably caused by a tree falling to the dinosaur[12], which was survived by the specimen.

Paleobiology

Parasaurolophus was a herbivorous dinosaur, probably browsing leaves, pine needles and wigs[13]. Its skull structure allowed to process the plant material with a grinding motion. The teeth of this dinosaur were continually being replaced. This dinosaur also had a beak, which was useful in cropping the foliage of plants, and also was able to held the food in its mouth by its cheek-like structure. By quadrupedal mode, Parasaurolophus could graze plants from the ground up to medium-sized bushes, and in bipedal mode it could reach the foliage of smaller trees up to 4 meters. Just like other lambeosaurines, its beak was considerably narrower than that of the hadrosaurines, suggesting that Parasaurolophus could have a more selective behaviour in feeding.

There were several earlier hypotheses concerning the function of the cranial crest of Parasaurolophus, which were later rejected. For example, several functions were suggested for the crest which were related to aquatic lifestyle[14][15]. Other proposals suggested that it was used as a weapon during combat amongst conspecifics[16], or it was joined to the vertebrae by ligaments or muscles in order to strenghten the support of the head[1]. Others supposed that it housed specialised glands or organs[17][18].

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Fossil skeleton of Parasaurolophus cyrtocristatus. By Lisa Andres from Riverside, USA - Field Museum Dinosaur, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=4121035

Wheeler was the first who proposed the possibility that the cranial crests of Lambeosaurinae could be in connection with thermoregulation[19]. Later Teresa Maryańska and Osmólska suggested that these dinosaurs could cool off by the help of their osmoregulation, using their salt-glands[20]. It is also hypothesized that that the function of the crest was to communicate or alert other conspecific group members, by using it as a resonating chamber which helped to produce low frequency sounds[7]. The crest of Parasaurolophus also might had an important role in visual communiction with other specimens of the species[21].

Scientific references

[1] Parks, W.A. (1922): Parasaurolophus walkeri, a new genus and species of trachodont dinosaur. University of Toronto Studies: Geological Series. 13: 5-32.

[2] Wiman, C. (1931): Parasaurolophus tubicen, n. sp. aus der Kreide in New Mexico. Nova Acta Regia Societatis Scientarum Upsaliensis. Series 4 (in German). 7 (5): 1-11.

[3] Ostrom, J.H. (1961): A New Species of Hadrosaurian Dinosaur from the Cretaceous of New Mexico. Journal of Paleontology. 35 (3): 575-577.

[4] Weishampel, D.B.; Jensen, J.A. (1979): Parasaurolophus (Reptilia: Hadrosauridae) from Utah. Journal of Paleontology. 53 (6): 1422-1427.

[5] Sullivan, R.S.; Williamson, T.E. (1999): A new skull of Parasaurolophus (Dinosauria: Hadrosauridae) from the Kirtland Formation of New Mexico and a revision of the genus. New Mexico Museum of Natural History and Science Bulletin. 15: 1-52.

[6] Williamson, T.E. (2000). Lucas, Spencer G.; Heckert, Andrew B. (eds.): Dinosaurs of New Mexico: Review of Hadrosauridae (Dinosauria: Ornithischia) from the San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin. 17: 191-213.

[7] Weishampel, D.B. (1981): Acoustic Analysis of Vocalization of Lambeosaurine Dinosaurs (Reptilia: Ornithischia) . Paleobiology. 7 (2): 252-261. doi:10.1017/S0094837300004036.

[8] Hone, D.W.E.; Naish, D.; Cuthill, I.C. (2011): Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs?. Lethaia. 45 (2): 139-156. doi:10.1111/j.1502-3931.2011.00300.x

[9] Horner, J.A.; Weishampel, D.B.; Forster, C.A. (2004): Hadrosauridae. In Weishampel, David B.; Osmólska, Halszka; Dodson, Peter (eds.). The Dinosauria (Second ed.). University of California Press. pp. 438-463. ISBN 978-0-520-24209-8.

[10] Glut, D.F. (1997): Parasaurolophus. In Glut, Donald F. (ed.). Dinosaurs: The Encyclopedia. McFarland & Company. pp. 678-940. ISBN 978-0-899-50917-4.

[11] Ostrom, J.H. (1961): A New Species of Hadrosaurian Dinosaur from the Cretaceous of New Mexico. Journal of Paleontology. 35 (3): 575-577.

[12] Bertozzo, Filippo; Manucci, Fabio; Dempsey, Matthew; Tanke, Darren H.; Evans, David C.; Ruffell, Alastair; Murphy, Eileen (2020): Description and etiology of paleopathological lesions in the type specimen of Parasaurolophus walkeri (Dinosauria: Hadrosauridae), with proposed reconstructions of the nuchal ligament. Journal of Anatomy. 238 (5): 1055-1069. doi:10.1111/joa.13363.

[13] Bakker, R.T. (1986): The Dinosaur Heresies: New Theories Unlocking the Mysteries of Dinosaurs and their Extinction. William Morrow. p. 194. ISBN 978-0-8217-2859-8.

[14] Romer, Alfred Sherwood (1933): Vertebrate Paleontology. University of Chicago Press. p. 491. OCLC 1186563.

[15] Wilfarth, Martin (1947): Rüsseltragende Dinosaurier. Orion (Munich) (in German). 2: 525-532.

[16] Abel, Othenio (1924): Die neuen Dinosaurierfunde in der Oberkreide Canadas. Jahrbuch Naturwissenschaften (in German). 12 (36): 709-716. doi:10.1007/BF01504818.

[17] Norman, David B. (1985): Hadrosaurids II. The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom. New York: Crescent Books. pp. 122-127. ISBN 978-0-517-46890-6.

[18] Evans, D.C. (2006): Nasal cavity homologies and cranial crest function in lambeosaurine dinosaurs. Paleobiology. 32 (1): 109-125. doi:10.1666/0094-8373(2006)032[0109:NCHACC]2.0.CO;2.

[19] Wheeler, P.E. (1978): Elaborate CNS cooling structure in large dinosaurs. Nature. 275 (5679): 441-443. doi:10.1038/275441a0.

[20] Maryanska, T.; Osmólska, H. (1979): Aspects of hadrosaurian cranial anatomy. Lethaia. 12 (3): 265-273. doi:10.1111/j.1502-3931.1979.tb01006.x.

[21] Hopson, J.A. (1975): The Evolution of Cranial Display Structures in Hadrosaurid Dinosaurs. Paleobiology. 1 (1): 21-43. doi:10.1017/S0094837300002165.