I've always been fairly certain that something similar to dragons have existed at some point, but I've always thought that they weren't as fantastic as the ones we see depicted today...probably more like a mere lumbering, land-bound beast, a general leviathan. The fact that dragons, or creatures similar to them, have been integral parts of vastly different and nonconnected cultures, as well as the Bible (read the book of Job), seem to point to there being a dragon-like creature at some time in our earth's history, and even more so, in the past ten or so millennia. I do not think they could fly or breathe fire (though I think that they may have had septic breath like komodo dragons, so toxic that it makes the creature breathed on feel a horrific burning sensation) but they were large lizards, possibly amphibious, and that what we see as the European dragon (long neck, wings, gigantic size) is an exaggeration passed down from generation to generation which has become the mainstream image of what dragons look like, while the wingless, snakelike dragons of asia are likely far closer to reality.