One of the world's largest collections of prehistoric rock art has been discovered in the Amazonian rainforest. Hailed as "the Sistine Chapel of the ancients", archaeologists have found tens of thousands of paintings of animals and humans created up to 12,500 years ago across cliff faces that stretch across nearly eight miles in Colombia. Their date is based partly on their depictions of now-extinct ice age animals, such as the mastodon, a prehistoric relative of the elephant that hasn't roamed South America for at least 12,000 years. There are also images of the palaeolama, an extinct camelid, as well as giant sloths and ice age horses. These animals were all seen and painted by some of the very first humans ever to reach the Amazon. Their pictures give a glimpse into a lost, ancient civilisation. Such is the sheer scale of paintings that they will take generations to study. The discovery was made by a British-Colombian team, funded by the European Research Council. Its leader is José Iriarte, professor of archaeology at Exeter University and a leading expert on the Amazon and pre-Columbian history. He said: "When you're there, your emotions flow … We're talking about several tens of thousands of paintings. It's going to take generations to record them … Every turn you do, it's a new wall of paintings. "We started seeing animals that are now extinct. The pictures are so natural and so well made that we have few doubts that you're looking at a horse, for example. It's fascinating."