The most terrifying of all dinosaurs were the theropods, a group that encompasses the fierce T-Rex. You can only imagine what early fossil hunters must have thought when they stumbled upon theropod bones. In fact, many experts believe that dinosaur remains may have given rise to belief in dragons, as ancient cultures attempted to account for fossils of creatures they had never seen alive. As for all the mythology behind fire-breathing and treasure hoarding, you can probably chalk that up to human imagination.