Parasaurolophus

Parasaurolophus had a large bony head crest that started at their nostrils and arched backward over their head. This prominent crest could grow up to 6 feet long and contained a series of hollow passageways. Parasaurolophus means "near crested lizard." The prevailing theory is that Parasaurolophus could make loud trumpeting calls using the hollow spaces in their crest. Paleontologists believe these dinosaurs had sensitive hearing, adding more evidence to the trumpeting calls theory. These calls could have been used to locate other members of their species or to alert others of danger. 

While Parasaurolophus mainly walked on all four legs, it was capable of standing on its back legs to reach higher vegetation or run from predators. They had a long, thick tail that helped them balance.

The discovery of a young Parasaurolophus shows that the head crest was present from an early age, but was smaller and more rounded than the adults' crests. Young Parasaurolophus would grow quickly and mature by the age of nine. Babies and juveniles likely lived and traveled with their parents and other adults in herds of varying sizes.