A subtropical rainforest, with Macginitiea trees and lygodium ferns, lines the red banks of a medium-size river. Crocodiles and aquatic plants fill the channel, and a pair of hippolike Coryphodon meander along the shore. Ten million years have passed since the rainforest first formed on the flanks of the Front Range. The world is now in the grip of an intense phase of global warming. There are no polar ice caps, and crocodiles and turtles live above the Arctic Circle. Credit: Denver Museum of Nature and Science