How did dinosaurs communicate?

Dinosaurs had large eyes and good hearing, so they were certainly capable of seeing and hearing one another. However we can tell a little more than this because some dinosaurs had very distinctive horns or crests on their heads. Animals today use features like this as signalling devices. Dinosaurs with horns, such as the ceratopians (Triceratops, Chasmosaaurus, Styracosaurus) no doubt used their horns and frills for signalling and for fighting. Other dinosaurs, particularly the duck-billed dinosaurs, give us other clues. One duck-billed dinosaur named Parasaurolophus has an extraordinarily long, curved, tubular crest on top of its head which could possibly have acted as a resonator so that the animal could have made a trombone-like bellow in life.