Animal tracks and rock deposits from northwest China suggest that dinosaurs adapted to the cold in the polar regions before a mass extinction event paved the way for their reign at the end of the Triassic. With a covering of fuzzy feathers to keep them warm, dinosaurs could better cope and take advantage of new lands when brutal conditions wiped out large swaths of more vulnerable creatures. “The key to their eventual dominance was very simple,” said Paul Olsen, the study’s lead author at the Lamont-Doherty Earth Observatory at Columbia University. “They were essentially cold-adapted animals. When it was cold everywhere, they were ready and other animals were not.” The first dinosaurs are thought to have appeared in the temperate south more than 230 million years ago, when most of the earth was a supercontinent called Pangaea. Dinosaurs were originally a minority group, living mainly at high altitudes. Other species, including the ancestors of modern crocodiles, dominated the tropics and subtropics. But at the end of the Triassic, about 202 million years ago, more than three-quarters of land and sea species disappeared in a mysterious mass extinction event linked to massive volcanic eruptions that sent much of the world into cold and darkness. The destruction set the stage for the reign of the dinosaurs. Writing in Science Advances, an international team of researchers explains how the mass extinction may have helped dinosaurs gain dominance. They started by looking at dinosaur tracks from the Junggar Basin in Xinjiang, China. These showed that dinosaurs were hiding along coastlines at high latitudes. By the end of the Triassic, the basin was well within the Arctic Circle, about 71 degrees north. But the scientists also found small pebbles in the usually fine sediments of the basin, which once contained several shallow lakes. The pebbles were identified as “ice-raft debris,” meaning they were washed away from lake shores on ice sheets before falling to the bottom when the ice melted. Together, the evidence shows that dinosaurs not only lived in the polar region, but thrived despite the freezing conditions. Having adapted to the cold, dinosaurs were poised to occupy new territories as dominant, cold-blooded species perished in the mass extinction. Stephen Brusatte, professor of palaeontology at the University of Edinburgh, who was not involved in the research, said dinosaurs were often described as beasts that lived in tropical jungles. The new research showed they would have been exposed to snow and ice at high latitudes, he said. “Dinosaurs would have lived in these frozen, frozen areas and had to deal with snow and frost and all the things that people living in similar environments have to deal with today. So how were the dinosaurs able to do it? Their secret was their wings,” he said. “The feathers of these early, primitive dinosaurs would have provided a stone coat to keep them warm in the high-latitude cold. And it seems those feathers came in handy when the world changed suddenly and unexpectedly and giant volcanoes began erupting at the end of the Triassic, plunging much of the world into cold and darkness during repeated volcanic-winter events.
