Fossil hunters trace the rise of the dinosaurs to the freezing winters that beasts endured as they roamed the far north.

Animal footprints and stone sediments from northwest China indicate that dinosaurs adapted to the cold of the polar regions before a mass extinction event paved the way for their reign at the end of the Triassic period.

With a blanket of misty feathers to help keep them warm, dinosaurs were better able to acclimatize and take advantage of new territories when brutal conditions wiped out vast swaths of the most vulnerable creatures.

“The key to their ultimate dominance was very simple,” said Paul Olsen, lead author of the study at Columbia University’s Lamont-Doherty Earth Observatory. They were basically cold-adapted animals. When it was cold all over, they were ready, and the other animals weren’t.”

It is believed that the first dinosaurs appeared in the temperate south more than 230 million years ago, when most of the Earth’s land formed a giant subcontinent called Pangea. Dinosaurs were initially a minority group that lived mainly at high altitudes. Other species, including the ancestors of modern crocodiles, dominated the tropics and subtropics.

But at the end of the Triassic period, about 202 million years ago, more than three-quarters of terrestrial and marine species were wiped out in a mysterious mass extinction event linked to massive volcanic eruptions that drove much of the world into cold and dark. The devastation paved the way for the era of the dinosaurs.

Writing science progress, an international team of researchers explains how the mass extinction helped the dinosaurs rise to dominance. They began by examining dinosaur footprints from the Jonggar Basin in Xinjiang, China. These studies showed that dinosaurs lurked along beaches at high latitudes. In the late Triassic period, the basin was located within the Arctic Circle, at about 71 degrees N.

But the scientists also found small pebbles in the fine sediments of a basin that once housed several shallow lakes. The pebbles have been identified as “ice-packed debris,” meaning they were carried away from lake banks on sheets of ice before falling to the bottom when the ice melted.

Together, the evidence suggests that dinosaurs not only lived in the Arctic, but thrived despite freezing conditions. Having adapted to the cold, the dinosaurs were preparing to take over new territories where the dominant, cold-blooded species died out in mass extinction.

Dinosaurs are often categorized as tropical jungle animals, said Stephen Brusatte, a professor of palaeontology at the University of Edinburgh who was not involved in the research. He said the new research showed they would have been exposed to snow and ice at higher latitudes.

“Dinosaurs would have lived in these frigid and icy regions and had to deal with snow, frostbite, and all the things that humans living in similar environments have to deal with today. So how did dinosaurs do that? Their secret was their feathers.”

“The feathers of these first primitive dinosaurs would have provided a soft coat to keep them warm in the high cold. These feathers then seem to have come in handy when the world suddenly and unexpectedly changed, and giant volcanoes began to erupt at the end of the Triassic period, resulting in Plunging most of the world into cold and darkness during frequent volcanic winter events.”