Via the Verge:

… These illustrations aren’t static — given the fast pace of scientific discovery, Csotonyi often has to update pieces to coincide with new revelations. The relatively new concept of feathered dinosaurs, in particular, has changed the way he renders these prehistoric giants. “I’ve had to return to several of my previous illustrations to update them as new information has become available based on increasingly informative fossil finds, and also because as young as my career is, I have learned to correct mistakes that I made earlier on,” he explains….