Let me know if I'd be better of going to one of the sister subreddits. Thanks!
this threads may answer that:
https://www.reddit.com/r/AskHistorians/comments/3iarqe/do_historians_know_why_we_see_dragon_mythology_in/
https://www.reddit.com/r/AskHistorians/comments/yfh6s/when_and_where_was_the_first_ever_reference_to/
https://www.reddit.com/r/AskHistorians/comments/vaq25/when_and_where_did_myths_about_dragons_appear/
https://www.reddit.com/r/AskHistorians/comments/1a1rny/why_are_there_old_english_and_chinese_dragons_but/
https://www.reddit.com/r/AskHistorians/comments/1a74qb/where_did_the_stories_of_dragons_come_from_how/
https://www.reddit.com/r/AskHistorians/comments/4453w8/how_did_virtually_all_precolumbian_cultures/
or Here be dragons from FAQ