Fossil hunters have traced the rise of the dinosaurs to the frigid winters the beasts endured as they roamed the far north.
Animal footprints and rock deposits from northwestern China suggest that dinosaurs adapted to the cold of the polar regions before a mass extinction paved the way for their reign at the end of the Triassic.
With a covering of downy feathers to help keep them warm, dinosaurs were better able to cope and take advantage of new territories when brutal conditions wiped out large groups of more vulnerable creatures.
“The key to their eventual dominance was very simple,” said Paul Olson, lead author of the study at Columbia University’s Lamont-Doherty Earth Observatory. “They were fundamentally cold-adapted animals. When it got cold everywhere, they were ready and the other animals weren’t.”
The first dinosaurs are thought to have appeared in the temperate south more than 230 million years ago, when most of Earth’s landmass made up a supercontinent called Pangea. Originally, dinosaurs were a minority group living mostly at high altitudes. Other species, including 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 were wiped out in a mysterious mass extinction linked to massive volcanic eruptions that sent much of the world into cold and darkness. The devastation ushered in the reign of the dinosaurs.
Writing in Science Advances, an international team of researchers explains how the mass extinction may have helped dinosaurs rise to dominance. They began by examining dinosaur footprints from the Junggar Basin in Xinjiang, China. They showed that dinosaurs lurked along coasts 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 usually fine sediments of the basin, which once contained several shallow lakes. The pebbles were identified as “ice shelf debris,” meaning they were washed up from the shores of the lake on ice sheets before falling to the bottom when the ice melted.
Together, the evidence suggests that dinosaurs not only lived in the polar region, but thrived despite the freezing conditions. Having adapted to the cold, dinosaurs were poised to conquer new territories as the dominant, cold-blooded species perished in the mass extinction.
Stephen Brusat, a professor of paleontology at the University of Edinburgh who was not involved in the research, said dinosaurs were often typified as beasts that lived in tropical jungles. The new research showed that they would have been exposed to snow and ice at high latitudes, he said.
“Dinosaurs would have lived in these cold, icy areas and would have had to deal with snow and frost and all the things that people living in similar environments have to deal with today. So how did the dinosaurs manage to do it? Their secret was their feathers,” he said.
“The feathers of these first, primitive dinosaurs would have provided a down coat to keep them warm in the high latitude cold. And those feathers seem to have come in handy when the world suddenly and unexpectedly changed and giant volcanoes began erupting at the end of the Triassic, plunging much of the world into cold and darkness during recurring volcanic winter events.
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