A couple of the horses here remind me of early horses I have seen in illustrations of early wildlife about 30,000 years ago. These drawings could be 10,000 to 30,000 years old. Water seeps into the caves over the millennia and damages these fine drawings. Bacteria also grows on the cave walls. Both of these processes damages the superficial layers of the cave walls causing thin layers of rock to flake off or to discolor the cave wall and these fine drawings.