Parasaurolophus

Parasaurolophus ("near crested lizard" ) is a hadrosaurid dinosaur that lived in the Late Cretaceous Period of North America.

Description
Parasaurolophus is estimated to have grown to a length of 10 meters and weighed up to 2.5 tonnes. Like other hadrosaurs, it could walk on both two and four legs. Skin impressions are known from P. walkeri, showing round, uniform scales.

The most distinctive feature of Parasaurolophus was its cranial crest. This crest was hollow, and differed slightly between species.

Classification
Parasaurolophus is a lambeosaurine hadrosaur, in the same subfamily as Corythosaurus and Lambeosaurus. Its closest relative is probably Charonosaurus, which has a similar skull. There are three known species, P. walkeri, P. cyrtocristatus, and P. tubicen.

This is a cladogram used in the 2007 redescription of Lambeosaurus:

History
The first specimen of Parasaurolophus was first discovered in what is now the Dinosaur Park Formation along the Red Deer River in Alberta, Canada in 1920. William Parks described the dinosaur as Parasaurolophus walkeri in 1922, in honor of Sir Edmund Byron Walker, who was Chairman of the Board of Trustees of the Royal Ontario Museum at the time. Its name means "near crested lizard" in reference to the observation that it looked superficially similar to Saurolophus ("crested lizard"). Not many specimens of the species have since been found, nor have many examples of the genus been found in Canada.

In 1921, paleontologist Charles H. Sternberg discovered a partial skull in the Kirtland Formation of New Mexico. The specimen was sent to Sweden, where Carl Wiman described it as P. tubicen. A second skull of the species was found in 1995 and described in 1999.

John Ostrom described another New Mexico specimen as P. cyrtocristatus in 1961. This species was the smallest of the genus, and possessed a shorter crest.

Diet
Parasaurolophus was a herbivore that ground its food in a fashion similar to chewing. It had hundreds of teeth packed into dental batteries, and had a beak at the end of its snout. Parasaurolophus could probably have eaten vegetation as high as 4 meters above the ground.

Head crest
The crest of Parasaurolophus likely had many different functions. Some of these include sexual selection, thermoregulation, and auditory signaling.