Prehistory Mystery

I like to read and think about Tyrannosaurus rex, and gigantic brontosaurus, with his long and slender neck. Pterodactyl was a reptile that flew just like a crow. I wouldn't want him overhead, with me stuck down below. Their skeletons are on display, so everyone can see 'em. They're in a place--I think it's called the dinosaur museum. I've seen these creatures on TV, in movies, and in books, so I guess someone must really know exactly how they looked. But I wish someone would tell me how they determined whether these critters were upholstered with hair, or scales, or maybe--feathers.