Parasaurolophus (; meaning "beside crested lizard" in reference to Saurolophus) is a genus of hadrosaurid "duck-billed" dinosaur that lived in what is now western North America and possibly Asia during the Late Cretaceous period, about 76.5–73 million years ago. It was a large herbivore that could reach over 9 metres (30 ft) long and weigh over 5 metric tons (5.5 short tons), and were able to move as a biped and a quadruped. Three species are universally recognized: P. walkeri (the type species), P. tubicen, and the short-crested P. cyrtocristatus. Additionally, a fourth species, P. jiayinensis, has been proposed, although it is more commonly placed in the separate genus Charonosaurus. Remains are known from Alberta, New Mexico, and Utah, as well as possibly Heilongjiang if Charonosaurus is in fact part of the genus. The genus was first described in 1922 by William Parks from a skull and partial skeleton found in Alberta. Parasaurolophus is a hadrosaurid, part of a diverse family of large Late Cretaceous ornithopods that are known for their range of bizarre head adornments, which were likely used for communication and increased hearing. This genus is known for its large, elaborate cranial crest, which forms a long curved tube projecting upwards and back from the skull in its largest form. Charonosaurus from China, which may have been its closest relative, had a similar skull and a potentially similar crest. Visual recognition of both species and sex, acoustic resonance, and thermoregulation have been proposed as functional explanations for the crest. It is one of the rarer hadrosaurids, known from only a handful of good specimens.
Discovery and naming
Meaning "near crested lizard", the name Parasaurolophus is derived from the Greek words para/παρα ("beside" or "near"), saurus/σαυρος ("lizard"), and lophos/λοφος ("crest"). It is based on ROM 768, a skull and partial skeleton missing most of the tail and the back legs below the knees, which was found by a field party from the University of Toronto in 1920 near Sand Creek along the Red Deer River in Alberta. These rocks are now known as the Campanian age Late Cretaceous period Dinosaur Park Formation. William Parks named the specimen P. walkeri in honor of Sir Byron Edmund Walker, the chairman of the Board of Trustees of the Royal Ontario Museum. Parasaurolophus remains are rare in Alberta, with only one other partial skull that is possibly from the Dinosaur Park Formation and three Dinosaur Park specimens lacking their skulls that possibly belong to the genus. In some faunal lists, there is a mention of possible P. walkeri material in the Hell Creek Formation of Montana, a rock unit of the late Maastrichtian age. This occurrence is not noted by Sullivan and Williamson in their 1999 review of the genus and has not been further elaborated upon elsewhere. In 1921, Charles H. Sternberg recovered a partial skull (PMU.R1250) from what is now known as the slightly younger Kirtland Formation in San Juan County, New Mexico. This specimen was sent to Uppsala, where Carl Wiman described it as a second species, P. tubicen, in 1931. The specific epithet is derived from the Latin word tǔbǐcěn, meaning "trumpeter". A second, nearly complete P. tubicen skull (NMMNH P-25100) was found in New Mexico in 1995. Using computed tomography of this skull, Robert Sullivan and Thomas Williamson gave the genus a monographic treatment in 1999 that covered aspects of its anatomy and taxonomy, as well as the functions of its crest. Williamson later published an independent review of the remains that disagreed with the taxonomic conclusions. John Ostrom described another good specimen (FMNH P27393) from New Mexico as P. cyrtocristatus in 1961. It includes a partial skull with a short, rounded crest and much of the postcranial skeleton except for the feet, neck, and parts of the tail. Its specific name is derived from the Latin words curtus, meaning "shortened" and cristatus, meaning "crested". The specimen was found in either the top of the Fruitland Formation or, more likely, the base of the overlying Kirtland Formation. The range of this species was described in 1979, when David B. Weishampel and James A. Jensen described a partial skull with a similar crest (BYU 2467) from the Campanian age Kaiparowits Formation of Garfield County, Utah. Since then, another skull has been found in Utah with the short, rounded P. cyrtocristatus crest morphology.
Species Parasaurolophus is known from three certain species: P. walkeri, P. tubicen, and P. cyrtocristatus. All of them can be clearly distinguished from each other and have many differences. The first named species, therefore the type, is P. walkeri. One certain specimen from the Dinosaur Park Formation is referred to it, but many more are almost certainly referable. Like stated above, it is different from the other two species, with it having a simpler internal structure than P. tubicen, along with a straighter crest and different internal structuring than P. cyrtocristatus. The next named species is P. tubicen, which is the largest of the Parasaurolophus species. It lived in New Mexico, where three specimens are known, and can be differentiated from its other species. It possesses a long and straight crest, with a very complex interior compared to the other species. All known specimens of P. tubicen come from the De-Na-Zin Member of the Kirtland Formation.
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