Dinosaurs have only been properly discovered and analysed quite recently, before then people thought they were bones of giants or dragons. Generally all that remains of this are the drawings of a 16th century Englishman or a mention of Dragons bones being found in a mountain in a Chinese chronicle, we don't really get the specimen itself. Dragons being large aerial creatures would of course not live in the same conditions that the classical dinosaurs that we find are discovered in, and so much like flying cats they would likely not survive into the fossil records. Both Dragons and flying cats would likely live in lofty mountains that have solid grounds and don't permit the fossils to seep into boggy soil and be preserved that way like most dinosaurs did. It is interesting that we lack fossils form the time from Scandinavia, well clearly something lived there, just what though? Clearly probably dragons that may have either failed to be preserved due to the climate and such or that was left more exposed in the mountainous and cold regions and discovered by early man leading to the dragon myths of the regions. It could even be said that many of these dragons that were found by people long ago in England and even China as well were actually just that, dragons. But of course they never looked after these dragon skeletons.