Ah, this thread. Excellent.
I have done much research on this topic. Much of it when I used to drink heavily, but that is beside the point.
The following is all the opinion of the Angry White Guy, and should not be regarded as actual fact. But if you don't agree, then you suck. ;D
Many cultures have stories of fantastic monsters. Many of these monsters are called "dragons". But if you read the descriptions of monsters, you will find that many of them resemble real creatures that actually existed, only they are now called "dinosaurs". The word "dinosaur" did not exist until the 19th century, but if you read any of the old stories and replace the word "dragon" with "dinosaur" the stories still make perfect sense.
Even the Bible talks about dinosaurs, in the book of Job. Leviathan and Behemoth. Some Biblical scholars have interpreted these stories as descriptions of crocodiles or hippos, but there is no way that those stories describe those animals. Hippos do not have "tails like cedars".
The Qur'an does not mention dinosaurs, but that doesn't mean that they didn't exist. We have the fossil evidence to prove that they did exist.
Now the hard part to accept comes if you believe the popular scientific theory of dinosaurs. Popular scientific opinion is that dinosaurs died out long before humans existed. So there is no way that humans could have fought and killed these "dragons" according to popular science.
So then where did the stories come from?