If you follow the news on things paleontological, you may have seen reports like this coming out in the press within the past few days:
And I’m going to tell you why this is most probably bullshit.
The finding they reference (paper here) is a fossilized syrinx (avian vocal organ) found in a late Cretaceous bird. Since this structure apparently can fossilize yet hasn’t been found in non-avian dinosaurs yet, the researchers conclude that non-avian dinosaurs didn’t have a syrinx like modern birds do. Fair enough, it might go to show that dinosaurs couldn’t make sounds exactly like those of birds.
However, what the reporters concluding from this that “dinosaurs couldn’t roar” don’t know enough to tell you is that syrinxes aren’t the only way animals make noise. In fact, most other tetrapods vocalize through a different organ called a larynx. That’s what we use, and that’s what crocodilians (the dinosaurs’ second-closest living relatives) use too. And presumably it’s also what every animal that can actually roar uses too. So as long as dinosaurs vocalized using a larynx rather than the avian syrinx, then yes, roaring would well remain within possibility for them. We may not know whether they did, since I don’t think a larynx is tissue that would fossilize easily, but since the larynx is found in all other reptiles excluding birds, it doesn’t seem unreasonable to suppose dinosaurs had that feature too.
So don’t worry, the new finding doesn’t say non-avian dinosaurs couldn’t roar. It only means they couldn’t tweet like birds.