Fossil hunters trace the rise of the dinosaurs to the cold winters the beasts endured as they roamed the far north.
Animal tracks and rock deposits from northwestern China show that dinosaurs adapted to the cold of the polar regions before the mass extinction, paving the way for their reign at the end of the Triassic period.
With a misty blanket of feathers to help keep them warm, dinosaurs were better able to acclimatize and exploit new territories when brutal conditions wiped out vast areas of the most vulnerable creatures.
“The key to their eventual dominance was very simple,” said Paul Olsen, lead author of the study at Columbia University’s Lamont-Doherty Earth Observatory. They were essentially cold-adapted animals. When everything was cold, they were ready, but the 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 Earth’s land mass formed a giant subcontinent called Pangea. Dinosaurs were originally 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 land and sea species were wiped out in a mysterious mass extinction event involving massive volcanic eruptions that plunged much of the world into cold and darkness. The devastation paved the way for the age of dinosaurs.
Writing scientific progress, an international team of researchers explains how the mass extinction helped dinosaurs dominate. They began by studying dinosaur footprints in the Jonggar Basin in Xinjiang, China. These studies showed that dinosaurs hid along beaches at high latitudes. During the Late Triassic period, the basin was located in the Arctic Circle, about 71 degrees north latitude.
But the scientists also found small pebbles in the fine sediments of the basin, which once contained several shallow lakes. The pebbles have been identified as “ice-packed debris,” meaning they were carried from the shores of the lake onto the ice sheets before falling to the bottom when the ice melted.
Taken together, the evidence suggests that dinosaurs not only lived in the Arctic, but thrived despite the freezing conditions. Adapted to the cold, the dinosaurs prepared to take over new territories where the dominant cold-blooded species died out in a mass extinction.
Dinosaurs are often classified as tropical jungle animals, said Stephen Brusatz, a professor of paleontology at the University of Edinburgh who was not involved in the study. He said the new study showed that at higher latitudes they would have been exposed to snow and ice.
“Dinosaurs would have lived in these cold and icy regions and had to contend with snow and frost and all the things that people living in similar environments face today. So how did the dinosaurs do it? Their secret was their feathers.”
“The feathers of these first primitive dinosaurs would have provided a soft coat to keep them warm in the extreme cold. These feathers seem to have come in handy when the world suddenly and unexpectedly changed and giant volcanoes started erupting at the end of the year. The Triassic period, which plunged most of the world into cold and darkness during frequent volcanic winter events.
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