I wonder if dragons are just a myth. On one hand, we have two different cultures, European and Asian, that seem to have "documentation" - in a manner of speaking - from about the middle ages, of the existence of some large, lizard-like or snake-like creatures. They're very scaly - usually green (just like some snakes and lizards), mean looking, and life-like. On the other hand, we've got these bone fossils that scientists have dug up; when they piece them together they get a picture of these large reptile-like and bird-like creatures. As far as I'm aware, all these types of fossils are considered dinosaurs; but I don't think I'm the only one who is amazed at the resemblances between dragons and dinosaurs. When dinosaurs are portrayed in drawings, they typically seem to be rather smooth-skinned, bland, cartoonish, and a little lifeless (but not so much when their bones are in a pose structure in a museum). Aside from the differences in some details, it's almost as though the two can corroborate each other. So what seems to be the problem with arguing that the two are identifying the same thing? Is there one, and why?
I think the problem, besides the potential claim that all fossils are dinosaurs (and implying that they all ceased to exist long before humans came into existence), is the way dragons are characterized by folklore and the drawings that are associated with them. The European version is a fire-breathing creatures with 2 legs, 2 arm-like appendages, and sometimes 2 wings. As far as I'm aware, there don't seem to be any vertebrates with more than 2 pairs of appendages in existence today (I'd be interested in finding out if there are). There also don't seem to be any organisms that can generate and aim (i.e., "breathe") fire - as in the chemical process of combustion, or a plasma.
Now let's put this into perspective. How many ostensive witnesses from the era of several centuries ago were biologists or any type of scientist? Even if they were, would they qualify or even be considered scientists or biologists by today's standards and criteria? I would surmise that if there were people encountering some large and hostile creatures back then, they were probably something like villagers being attacked by them, or knights in shining armor who were deployed to fight and destroy them. In either case, they're either people who had a fear of being attacked and eaten by these giant monsters, or warriors who were trained to try to chop its head off, and didn't have an understanding of biology like we do today - or of reality in general.
If that were the case, then these people probably didn't consider stopping and looking at it to observe many details about it. For example, it could have been that these monsters in question could jump very high, so it seemed like they could fly. They probably noticed that animals which could fly, such as birds, bees, and flies, had wings. This probably inspired the artists' renditions of dragons from back then to include wings. Notice how small they typically seem to be in relation to the rest of the body; would such a creature be able to use them to fly? Perhaps they were confusing a sail for a wing structure, since they probably didn't know any better. Another example could be that they didn't differenciate one type or species of dinosaurs from another, such as a spinosaurus-like creature that ran around and attacked them from a pteranodon-like creature that flew around and attacked them.
As far as the fire-breathing issue is concerned, I don't think it's very difficult to find an explanation for that. Consider that there are animals that inject venom, such as snakes and spiders. When bitten, people generally attribute the pain as a burning sensation in some cases. Now, why would they use the word burn if they know there is no fire involved? I'd say it's because the two forms of pain feel the same, not because venom is fire. If a person from the middle ages with limited scientific knowledge and understanding were attacked by some acid-spitting dilophosaurus-like creature, wouldn't they also describe the pain as burning and maybe even be under the impression of being shot with a flame thrown from its mouth? I'd think so. We do know of a creature that has a defense mechanism of spraying an unpleasant chemical and making a banging sound - the bombadier beetle. There are also fish that can shoot a stream of water to knock their prey off of a leaf and into the water. I believe that these cases can illustrate, when you combine the features, that there may be or have been creatures capable of achieving what may seem to be the ability to throw a flame.