From Edward N. Haas:

Re: Killed twice in 1600s, hoax “dragon” slain again-in crea (May 8, 2013): The notion of dragons goes back even to very ancient times, and that fact has amazed many, because the notion of a dragon bears strong resemblance to modern depictions of some kinds of dinosaurs. In its article “Dragon” on page 209 of volume 4 of its 1992 edition, “Encyclopedia Britannica “puzzles over how “The belief in these creatures apparently arose without the slightest knowledge on the part of the ancients of the gigantic, prehistoric, dragon-like reptiles.” As Britannica points out on page 315 of vol. 17 of its 1992 edition, “there was no concept of anything like a dinosaur” prior to 1841. Whence comes this 5, 000 year old, startling similarity of dragons to creatures which, supposedly, were wholly unknown before 1841? An interesting explanation is found in a book by Wilhelm Bousset entitled “The Antichrist Legend” and translated by A. H. Keane in 1896. To the front of the book, Mr. Keane attached his own explanation of how the dinosaur like imagery of dragons came about in ancient Babylon. According to Mr. Keane, it all started when humanity switched to living off of crops and, therefore, had to grow food along the banks of serpentine rivers which often flooded and thereby brought large alligators into conflict with the human race. Stories of dragons, then, are, according to Mr. Keane, the way our ancient ancestors memorialized the troubles inflicted upon them by winding rivers and large alligators.