Parasaurolophus, meaning “near-crested lizard,” is a genus of ornithopod dinosaur from the Late Cretaceous Period of what is now North America (76 to 73 million years ago). This genus is based on a skull and partial skeleton missing most of the tail and hind 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, Canada. The rocks where the specimen was unearthed are known as the Campanian-age Upper Cretaceous Dinosaur Park Formation.
The type species, P. walkeri, was named in honor of Sir Byron Edmund Walker, Chairman of the Board of Trustees of the Royal Ontario Museum, by William Parks. Remains of Parasaurolophus are quite rare in Alberta, with only one other partial skull pulled from the Dinosaur Park Formation, and three specimens lacking skulls, possibly belonging to the genus.
A second species, named P. tubicen in 193, was found in 1921 by Charles H. Sternberg at the Kirtland Formation in San Juan County, New Mexico. Another specimen was described and given the species name P. cyrtocristatus in 1961. The range of the species was expanded in 1979, when David B. Weishampel and James A. Jensen described a partial skull from the Campanian-age Kaiparowits Formation of Garfield County, Utah. Another similar specimen has since been found in the same formation in Utah.
Parasaurolophus was an herbivore that walked both as a biped and a quadruped. It is a hadrosaurid, part of a diverse family of Cretaceous dinosaurs known for their range of bizarre head crests, which at their largest forms long curved tubes projecting upwards and back from the skull. The consensus is that major functions of the crest included visual recognition of both species and sex, acoustic resonance, and thermoregulation. It is one of the rarer duckbills, known from only a handful of good specimens.
As is the case with most dinosaurs, the skeleton of Parasaurolophus is not completely known. The estimated length of the type species is 31 feet. The skull is about 5.2 feet long, including the crest. However, the skull of P. tubicen measured over 6.6 feet long, indicating it was a larger animal than P. walkeri. The average weight of Parasaurolophus was 2.7 tons.
Although being both a biped and quadruped, Parasaurolophus probably preferred to forage for food on four legs. When in motion, however, it ran quickly on two legs, fleeing from predators.
The most noticeable feature of Parasaurolophus was its cranial crest, which protruded from the rear of the head and was made up of the premaxilla and nasal bones. The type specimen has a notch in the neural spines near where the crest would hit the back, but this may relevant only 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 this 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.