Asked by: Roger Sayers, Tunbridge Wells
There is no way to tell from a fossil whether the animal was sleeping when it died or not. But it seems likely that the four-legged dinosaurs probably mostly slept standing up to allow them to respond to predators more rapidly. Two-legged dinosaurs like T-Rex almost certainly lay down though. Balancing while you are asleep is just too tricky.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.