English: Parasaurolophus walkeri is a hadrosaur from the Late Cretaceous known for its large cranial crest. The purpose of this crest is the topic of much debate, with theories including visual recognition of both species and sex, acoustic resonance, and thermoregulation. Parasaurolophus grew to around 9 m in length, and had an estimated weight of somewhere between 3-5 t. Like other hadrosaurs, Parasaurolophus was facultatively bipedal, meaning it was able to walk on two legs or four. It probably preferred to forage for food on four legs, but ran on two.