How dinosaurs conquered the world by doing the unthinkable

Dinosaurs are often thought of as creatures thriving in warm climates and lush tropical jungles. But now, new research challenges this idea: Rather, dinosaurs endured freezing temperatures, which ultimately allowed them to reign in the Jurassic. 

The study's lead author, paleontologist Paul Olsen, ventured out to the Junggar basin in China in 2016, a region rich in dinosaur fossils and footprints. On the very first day, and at their very first stop, Olsen’s team stumbled upon something much coarser than sand and gravel. It seemed quite unusual to Olsen.

"We didn't move for three hours arguing about what this is," Olsen, who led the research published in the journal Science Advances, told Mashable. 

"The whole picture of dinosaurs is backward. They're primarily cold-adapted animals."

The research team narrowed the curious deposits down to "ice-rafted debris," which are sediments containing pebbles that formed some 206 million years ago. (Ice amassed in the water next to land, ultimately transporting and dropping terrestrial rocks lodged in the ice to a lake bottom.) Its presence in the area indicates floating ice once existedin a region where dinosaurs roamed, and left clear tracks. The researchers also determined the Junggar basin was located above the Arctic circle, meaning it was extremely cold there, particularly in the winter. 

"The whole picture of dinosaurs is backward. They're primarily cold-adapted animals," Olsen emphasized. 

SEE ALSO: Scientists reveal the wild history of Earth’s CO2 since the dinosaurs died

Dinosaurs first appeared in the Triassic Period some 230 million years agowhen Earth was a single, giant landmass called "Pangea." At the end of the Triassic, massive volcanic eruptions caused the planet's temperature to skyrocket. Carbon dioxide levels (which trap heat on Earth) soared and the oceans became extremely acidic. These conditions proved inhospitable to most species; the fossil record shows three out of every four land and ocean species went extinct. Yet the dinosaurs somehow survived, and then ruled the Jurassic era.

How exactly they succeeded has been a mystery. 

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But Olsen’s study now offers an explanation: The same volcanic eruptions that spewed huge amounts of heat-trapping carbon dioxide into the atmosphere also released the chemical sulfur dioxide, which blocks sunlight.

This triggered a dimming of Earth and caused decade-long periods of plummeting, freezing temperatures called "volcanic winters." Crucially, the drops in temperature during severe volcanic winter snaps were far great than the rise in temperature from carbon dioxide emissions. 

Scientists found ice-rafted sediments in China's Junggar basin, a clear sign of cold climes. Credit: Paul Olsen

Feather-like adaptation to cope with freezing temperatures

Many uninsulated land animals, notably in the tropics, couldn’t adapt to these fierce cold snaps and went extinct, including a crocodile-like species closely related to dinosaurs. But the dinosaurs survived with a unique adaptation, said Olsen. 

Dinosaurs, like birds, were insulated. Similar to birds' feathers that protect them from cold, dinosaurs also had a feather-like structure called "protofeathers" that they inherited from their ancestors. (The largest dinosaurs, however, didn't need feathery insulation, as they were simply gigantic and had high metabolic rates, Olsen told Mashable.)

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"I thought the study was exciting because it's another story from another time that challenges the dinosaurian stereotype."

With their competition largely eliminated, the dinosaurs ultimately took over some 200 million years ago, both herbivores and carnivores alike.

Cold-adapted plants thrived during this period, allowing herbaceous dinosaurs to flourish. "The rich vegetation allowed herbivores to survive the winters. And that, of course, was food for the carnivores," Olsen explained. 

Amid snow and freezing temperatures, a dinosaur captures mammalian prey. Credit: Larry Felder

The discovery could rewrite our understanding of the dinosaurs' dominance in the Jurassic. "I thought the study was exciting because it's another story from another time, that challenges the dinosaurian stereotype," said Anthony Fiorillo, a paleoecologist at Southern Methodist University who was not involved in the study. "Their insulation mechanism was especially very interesting," Fiorillo, who researches Arctic dinosaurs, told Mashable. 

In freezing climes, dinosaurs also likely adapted. The growth of dinosaurs could have slowed during the cold months in the Arctic compared to the warmer months, Fiorillo explained. The fossilized bones have markings called bone rings, similar to tree rings, indicating when they temporarily stopped growing. This allowed the animals to conserve energy during harsh winters when food resources diminished.

Olsen and his team plan to continue looking for the compelling evidence (ice-rafted debris) that suggests dinosaurs thrived in colder climes. Stay tuned: Our understanding of the reign of the dinosaurs is still being written.