I saw something on NGC a while back that got me thinking about this topic. Wheter or not dragons really existed or not.
Dragons have existed in many different cultures. From ancient Babylon to the times of knights in Europe. While the appearances have changed, they pretty much have the same effect on the populous. In China, the dragon had a long slender body with five digits on each foot. It breathed fire and was reveared as a protector of the ruling family. In Japan, the dragon appeared more like a fish, dwelling in bodies of water. In ancient Europe, dragons had a more lizard like body, with a larger hind section and was mostly quadrapedal. The dragons of ancient Europe also had the ability to fly and terrorize the people, which were protected by the knights.
It was a very intriguing show, until the end. They stated that dragons were not real, but perhaps the misgivings of locals who happend to stumble upon the bones of dinosaurs and they couldn't decipher what they really were.
I believe this: Dragons at some point in time were in fact real. Now they didn't live among humans, but perhaps sometime during the time of the dinosaurs. The similiarities of all the dragon stories are in fact a little to similar to disprove they were not real.