Fossil hunters have traced the rise of dinosaurs to the freezing winters when animals endured as they roamed the far north.
Animal footprints and stone deposits from northwest China suggest that dinosaurs adapted to the cold in the polar regions before a mass extinction event at the end of the Triassic paved the way for their reign.
Dinosaurs were better able to deal with downy feathers to help keep them warm, and better exploit new territories when brutal conditions wiped out a large area of more vulnerable creatures.
“The key to their eventual dominance was very simple,” said Paul Olsen, lead author of the study at the Lamont-Doherty Earth Observatory at Columbia University. “They were basically animals adapted to the cold. When it got cold everywhere, they were ready and the other animals were not.”
The first dinosaurs are thought to have emerged more than 230 million years ago in the temperate south, when most of Earth’s landmass formed a supercontinent called Pangea. Dinosaurs were originally a minority group that lived mostly at high altitudes. Other species, including the ancestors of modern crocodiles, ruled 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 disappeared in a mysterious mass extinction event associated with massive volcanic eruptions that sent much of the world into cold and darkness. The destruction laid the groundwork for the reign of the dinosaurs.
to write Science Advances, an international team of researchers explains how the mass extinction may have helped dinosaurs become dominant. They started by examining dinosaur footprints from the Junggar Basin in Xinjiang, China. These showed that dinosaurs lurked along coastlines at high latitudes. In the Late Triassic, the basin stretched within the Arctic Circle, about 71 degrees north.
But scientists have also found small pebbles in the normally thin sediments of the basin that once housed several shallow lakes. The pebbles have been described as “ice-shelf debris,” meaning they were carried over ice sheets from lake edges before falling to the bottom when the ice melted.
Together, the evidence shows that dinosaurs not only lived in the polar region, but thrived despite freezing conditions. Cold-adapted dinosaurs were poised to conquer new territories as dominant, cold-blooded species perished in the mass extinction.
Stephen Brusatte, a professor of paleontology at the University of Edinburgh, who was not involved in the research, said dinosaurs often looked like monsters that lived in tropical forests. The new research showed they would be exposed to snow and ice at high latitudes, he said.
“Dinosaurs lived in these cold, icy regions and had to deal with snow and frostbite and everything that humans living in similar environments have to deal with today. How did the dinosaurs do this? Their secret was their feathers,” he said.
“The feathers of these early, primitive dinosaurs would have provided a furry coat to keep them warm in the high latitude cold. These feathers seem to have formed much of the earth during repeated volcanic-winter events when the world suddenly and unexpectedly changed and giant volcanoes began to erupt at the end of the Triassic. it worked when you dragged it into the cold and the dark.
