I will never forget seeing
In a paper recently published in the journal Historical Biology, Senter reviewed the evolution of animal sounds during the Paleozoic (about 542 to 251 million years ago) and Mesozoic (about 251 to 65 million years ago). Insects were among the first sound makers, but what about dinosaurs? Unfortunately, we cannot study a living Triceratops, Apatosaurus, or Albertosaurus to find out, but crocodylians and birds (the closest living relatives of dinosaurs) might provide some clues.
According to Senter, crocodylians vocalize by using their larynx, a soft-tissue structure in the throat that does not fossilize. Since all the different types of living crocodylians (alligators, crocodiles, and gharials) vocalize this way, it is probable that their common ancestor that lived during the Late Cretaceous did too, but whether their even earlier relatives could do so is unknown.
Birds, on the other hand, vocalize through an organ in their throat called the syrinx. This is a different organ from the larynx of crocodylians, and thus Senter argues that vocalization in the two groups evolved independently. This would mean that the last common ancestor of birds and crocodylians (which would also be an ancestor of dinosaurs and pterosaurs) might not have been able to vocalize at all.
Could some dinosaurs have independently evolved the ability to vocalize, just as birds and crocodylians did? Researchers like David Weishampel have, after all, demonstrated the potential use of hadrosaur crests as resonating chambers when the animals wanted to communicate over long distances. Recent research presented at last year's annual Society of Vertebrate Paleontology meeting, too, suggests that at least some hadrosaurs could have been communicative creatures. Indeed, dinosaurs may not have vocalized the same way that crocodylians or birds do, and even if their soft-tissue vocalization organs were not preserved, scientists can still study their fossilized inner ears to try and understand what sounds they might have been able to hear. A dinosaur with sensitive ears, for example, might have been more communicative, but unfortunately there are no living non-avian dinosaurs to test this idea.
Did dinosaurs sound just like they do in the movies? Probably not, especially since most "dinosaur" sounds you hear are actually mash-ups of vocalizations made by different modern animals. Since the organs they would have used to vocalize with did not fossilize, however, we may never know what kind of sounds they made (if they were able to make them at all). Given the difficulty getting at this question, then, I say that we should continue to let hadrosaurs bellow and tyrannosaurs roar until we find hard evidence that they could not.