Where did Dragon Lore Come From?

Perhaps this is more of a GQ, but considering that literature and film play a large part in the question, I’m going to try it in this forum.

Hubby reads a lot of sci-fi/fantasy, and the other day, we started discussing dragons, and the various ways they’re portrayed in novels and movies, as well as in historical legend. He pointed out that several cultures have ancient stories and legends of dragons.

What is the root? The portrayals seem somewhat uniform. What’s the earliest mention of dragons in written legend, and what in the world could have inspired it?

I don’t know it previous threads help, but http://boards.straightdope.com/sdmb/showthread.php?&threadid=10909

http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=158210&highlight=dragons
There are numerous others.

You might want to check out The Flight of Dragons, which attempts to come up with a scientific basis for dragons as described in folk legend. I don’t think the guy actually believes this stuff, but he does a good job of not “breaking character.”

I wonder if the idea of dragons came about when ancient peoples found dinosaur bones but couldn’t connect them with any actual living creatures.