Fossil hunters have traced the rise of the dinosaurs back to the freezing winters the beasts endured while roaming around the far north.
Footprints of the animals and stone deposits from north-west China suggest dinosaurs became adapted to the cold in 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 help keep them warm, the dinosaurs were better able to cope and to take advantage of new territories when brutal conditions wiped out great swaths of more vulnerable creatures.
“The key to their eventual dominance was very simple,” said Paul Olsen, the lead author on the study at the Lamont-Doherty Earth Observatory at Columbia University. “They were fundamentally cold-adapted animals. When it got cold everywhere, they were ready, and other animals weren’t.”
The first dinosaurs are thought to have emerged in the temperate south more than 230m years ago, when most of Earth’s land made up a supercontinent called Pangaea. The dinosaurs were initially a minority group, living mainly at high altitudes. Other species, including ancestors of modern crocodiles, dominated the tropics and subtropics.
But at the end of the Triassic, about 202m years ago, more than three-quarters of land and marine species were wiped out in a mysterious mass extinction event linked to vast volcanic eruptions that sent much of the world into cold and darkness. The devastation set the stage for the reign of the dinosaurs.
Writing in Science Advances, an international team of researchers explain how the mass extinction may have helped the dinosaurs rise to dominance. They began by examining dinosaur footprints from the Junggar Basin in Xinjiang, in China. These showed that dinosaurs lurked along shorelines at high latitudes. In the late Triassic, the basin lay well within the Arctic Circle, at about 71 degrees north.
But the scientists also found small pebbles in the normally fine sediments of the basin, which once held several shallow lakes. The pebbles were identified as “ice-rafted debris”, meaning they were carried away from the lakesides on sheets of ice before falling to the bottom when the ice melted.
Together, the evidence suggests dinosaurs not only lived in the polar region, but thrived despite freezing conditions. Having adapted to the cold, the dinosaurs were poised to take over new territories as dominant, cold-blooded species perished in the mass extinction.
Stephen Brusatte, a professor of palaeontology at the University of Edinburgh, who was not involved in the research, said dinosaurs were often typecast 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 frigid, icy areas and would have had to cope with snow and frostbite and all the things that humans living in similar environments have to deal with today. So how were dinosaurs able to do it? Their secret was their feathers,” he said.
“The feathers of these first, primitive dinosaurs would have provided a downy coat for keeping them warm in the high-latitude chill. And it seems these feathers then came in handy when the world suddenly and unexpectedly changed, and giant volcanoes began to erupt at the end of the Triassic, plunging much of the world into cold and darkness during repeated volcanic-winter events.”