Fossil hunters have traced the rise of dinosaurs to the frigid winters the beasts endured on their forays into the far north.
Animal footprints and stone deposits from northwestern China suggest that dinosaurs had adapted to the cold in polar regions before mass extinctions paved the way for their domination at the end of the Triassic.
With a covering of fluffy feathers to keep them warm, the dinosaurs were better able to navigate new territories and take advantage when brutal conditions wiped out large swathes of vulnerable creatures.
“The key to their eventual dominance was very simple,” said Paul Olsen, the study’s lead author at Columbia University’s Lamont-Doherty Earth Observatory. “These were basically cold-adapted animals. When it got cold everywhere, they were ready, other animals were not.”
The first dinosaurs are believed to have appeared in the temperate south more than 230 million years ago, when most of the earth formed a supercontinent called Pangea. The dinosaurs were originally a minority 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 202 million years ago, more than three-quarters of land and sea life was wiped out in a mysterious mass extinction event linked to massive volcanic eruptions that plunged much of the world into cold and darkness. The devastation paved the way for dinosaur domination.
In Science Advances, an international team of researchers explains how the mass extinction may have helped dinosaurs become supreme. They began studying dinosaur footprints from the Junggar Basin in Xinjiang, China. These showed that dinosaurs lurked along coasts at high latitudes. In the late Triassic, the basin was 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 contained several shallow lakes. The pebbles have been identified as “ice raft debris,” meaning they were carried away from the lake shores on sheets of ice before falling to the bottom as the ice melted.
Taken together, the evidence suggests that dinosaurs not only lived in the polar region, but thrived despite frigid conditions. Having adapted to the cold, dinosaurs were poised to conquer new territories as dominant, cold-blooded species perished in mass extinctions.
Stephen Brusatte, a professor of paleontology at the University of Edinburgh who was not involved in the research, said dinosaurs are often referred to 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 cold, icy areas and would have had to deal with snow and frostbite and all the things that humans living in similar environments have to deal with today. How could the dinosaurs do that? Her secret was her feathers,” he said.
“The feathers of those first, primitive dinosaurs would have provided a downy coat to keep them warm in the cold of the high latitudes. And it seems these feathers came in handy when the world changed suddenly and unexpectedly, and huge volcanoes began erupting at the end of the Triassic, dumping much of the world into cold and darkness during repeated volcanic winter events.”