[Lurking Libertarian]

Have paleontologists dug up many fossils and skeletons of these various species of dinosaurs? Do they in fact have a very good idea, if not definite knowledge, of the physical appearance of these animals? Since the answers to both of those questions is "yes," then we know those ancient drawings are in fact of real dinosaurs who we know for a fact once existed. I think your argument needs work.

You don't have to be a paleontologist to dig up dinosaur bones. The ancient Greeks found fossils, and knew they were bones of animals that they didn't see walking around. No reason to think the Indians didn't find bones of "dragons," and didn't repeat stories about those discoveries.

[Future Snake Eater]

No reason to think the Indians didn't find bones of "dragons," and didn't repeat stories about those discoveries.

...which would be a great explanation if we were talking about stories, but we're talking about actual drawings made by people thousands of years ago that clearly depict dinosaur species that have been discovered by more modern day scientists. How could these ancient peoples have known what dinosaurs looked like if they could never have seen one? Could they extrapolate their appearance based on a couple of bones? I doubt it.