Parasaurolophus was a hadrosaur. They had a large head crest, which was a long curved tube. It went upwards and back from the skull. The crest has been much discussed by scientists. They think its main functions were visual recognition of species and sex, acoustic resonance (making a loud sound), and thermoregulation. Parasaurolophus is one of the rarer hadrosaurs: there are only a few good specimens.