Singing "Raptors"

Though that doesn't explain why Skull (and everyone else, for that matter) can talk. Not to mention we've seen him sing before. Go figure.

For a while, the answer to "Could dinosaurs vocalize?" was, "Sure, why not?" After all, both living dinosaurs (neornithines) and their closest living relatives (crocodilians) vocalize. But there's a catch. These two groups do not use the same organ for vocalization, meaning they evolved vocalization independently and their latest common ancestor likely couldn't vocalize at all! In crocodilians, vocal sounds are made by the larynx, while birds have an organ called the syrinx. We don't know how when crurotarsans evolved their larynx, because there are no skeletal features that correspond to this organ. However, there is a way to tell if a syrinx is present in extinct archosaurs, and that is the presence of the clavicular air sac that is required for the syrinx to function. As it turns out, although all saurischians have air sacs, only ornithothoracines (enantiornithines, hesperornithines, yanornithiforms, neornithines, and some intermediate taxa) have the clavicular air sac. (The carnosaur Aerosteon had a clavicular air sac, but this was likely evolved independently of the one ornithothoracines have.) That means non-ornithothoracine dinosaurs did not possess a syrinx and were probably not able to make vocal sounds. In fact, this might help explain why so many different dinosaur groups evolved so many different visual display structures.

Fans of roaring tyrannosaurids, screaming deinonychosaurs, and groaning sauropods, your childhood has just been ruined forever. But don't despair, as there are other means for non-ornithothoracine dinosaurs to have communicated acoustically. Mechanical ways of sound making such as foot stomping, wing beating, jaw snapping, hissing, and splashing are certainly not out of the question. And the traditional idea of trumpeting hadrosaurs may still be safe; you don't need vocal chords to blow a musical instrument, fortunately.

Nonetheless, I don't think we'll be seeing non-roaring tyrannosaurids on screen anytime soon. Reality is unrealistic. Thank the coconut effect.

Edit: See comments (and addendum).