Fossil hunters have traced the rise of the dinosaurs back to the frigid winters the beasts endured as they roamed the far north.
Animal tracks and stone deposits from northwestern China suggest that dinosaurs adapted to the cold in the polar regions before a mass extinction paved the way for their reign at the end of the Triassic.
With a covering of shaggy feathers to help keep them warm, the dinosaurs were better able to cope and take advantage of new territories when brutal conditions wiped out large swaths of the most vulnerable creatures.
“The key to its eventual dominance was very simple,” said Paul Olsen, lead author of the study at the Lamont-Doherty Earth Observatory at Columbia University. “They were fundamentally cold-adapted animals. When it was cold everywhere, they were ready and other animals were not.”
The first dinosaurs are thought to have emerged in the temperate south more than 230 million years ago, when most of Earth’s land formed a supercontinent called Pangea. Dinosaurs were initially a minority group that lived primarily at high altitudes. Other species, including the ancestors of modern crocodilians, dominated the tropics and subtropics.
But at the end of the Triassic, some 202 million years ago, more than three-quarters of terrestrial and marine species disappeared in a mysterious mass extinction event linked to vast volcanic eruptions that plunged much of the world into cold and darkness. The devastation set the stage for the reign of the dinosaurs.
writing in Progress of science, an international team of researchers explains how the mass extinction may have helped dinosaurs rise to dominance. They began by examining dinosaur tracks from the Junggar Basin in Xinjiang, China. These showed that dinosaurs lurked along coastlines at high latitudes. In the late Triassic, the basin lay well within the Arctic Circle, 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 were identified as “ice raft-borne debris,” meaning they were washed 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 the freezing conditions. Having adapted to the cold, the dinosaurs were poised to take over new territories as the dominant cold-blooded species perished in mass extinction.
Stephen Brusatte, a professor of palaeontology at the University of Edinburgh, who was not involved in the research, said dinosaurs were often pigeonholed as beasts that lived in tropical rainforests. 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 deal with snow and freezing and all the things that humans living in similar environments have to deal with today. So how could the dinosaurs do it? His secret was his feathers,” he said.
“The feathers of these early primitive dinosaurs would have provided a soft coat to keep them warm in the cold of high latitudes. And it seems that these feathers later came in handy when the world changed suddenly and unexpectedly, and giant volcanoes began erupting at the end of the Triassic, plunging much of the world into cold and darkness during repeated volcanic winter events.” .
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