There's lots of ancient literature from all around the world regarding giant reptilian-like beasts. Dragons didn't just spring from people's imaginations, they witnessed strange beasts, some of them giant, and exaggerated them over the generations into something altogether fanciful. But you take the legends at their most base level - someone battling/killing a great reptilian-like beast. There are ancient sculptures and engravings etc. This isn't some nut-job cryptology belief, this is something together far more plausible.