"Saint George Killing the Dragon" by Bernat Martorell (1430-1435)
The artist's intent: To depict his patron Saint delivering the death blow to the legendary dragon of the Middle East.
The outcome: A feathered dinosaur. There is much academic debate over whether the prominence of dragons in practically every culture's mythology is due to our ancestors stumbling upon dinosaur fossils and being all, "This exists? Uh oh." What makes this painting unique over the dozens of other depictions of Saint George slaying the dragon is that Martorell decked his dino out in feathers. Paleontologists now believe that even giant carnivores like T-Rex likely sported feathers, at least as juveniles. That's a pretty amazing, if accidental, prediction for a dude hanging around in the 15th Century!