How dinosaurs conquered the world by doing the unthinkable

Dinosaurs are often thought of as creatures that thrived in warm climates and lush tropical forests. But now, new research is challenging this idea: Instead, dinosaurs experienced freezing temperatures, which eventually allowed them to rule in the Jurassic.

The study’s lead author, paleontologist Paul Olsen, ventured into China’s Junggar basin in 2016, an area rich in dinosaur fossils and footprints. On day one, and on their first stop, Olsen’s team came across something much rougher than sand and gravel. It seemed very unusual to Olsen.

“We didn’t budge for three hours debating what this was,” Olsen, who led the study published in the journal Science Advancesto Mashable.

“The whole dinosaur picture was underdeveloped. They were primarily cold-adapted animals.”

The research team narrowed down the strange deposits to “ice raft debris,” which are gravel-bearing sediments that formed about 206 million years ago. (Ice accumulates in the water next to land, eventually transporting and dropping the terrestrial rock that lodges in the ice to the bottom of the lake.) Its presence in the area shows floating ice ever existed in areas where dinosaurs roamed, and left clear trails. The researchers also determined that the Junggar basin lies above the Arctic circle, which means it is very cold there, especially in winter.

“The whole dinosaur picture was retarded. They were primarily cold-adapted animals,” Olsen emphasizes.

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Dinosaurs first appeared in the Triassic Period about 230 million years ago when Earth was a single giant landmass called “Pangea.” At the end of the Triassic, a massive volcanic eruption caused the planet’s temperature to skyrocket. Levels of carbon dioxide (which traps heat on Earth) spiked and the oceans became very acidic. These conditions proved inhospitable to most species; The fossil record shows three out of every four terrestrial and marine species extinct. But the dinosaurs somehow survived, and went on to rule the Jurassic era.

How exactly they succeeded has been a mystery.

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

This triggered the dimming of the Earth and caused a decade-long period of freezing temperatures called the “volcanic winter.” Importantly, the drop in temperature during a severe volcanic winter far outweighs the increase in temperature from carbon dioxide emissions.

Scientists found ice raft sediments in China’s Junggar basin, a clear sign of a cold climate.
Credit: Paul Olsen

Feather-like adaptations to cope with freezing temperatures

Many uninsulated land animals, especially in the tropics, could not adapt to the harsh cold and became extinct, including crocodile-like species closely related to dinosaurs. But dinosaurs survived with unique adaptations, Olsen said.

Dinosaurs, like birds, were isolated. Similar to the feathers of birds that protected them from the cold, dinosaurs also had feather-like structures called “protofeathers” that they inherited from their ancestors. (The largest dinosaurs, however, didn’t need furry isolation, as they were just giants and had high metabolic rates, Olsen told Mashable.)

“I think this research is interesting because it’s another story from another time that challenges dinosaur stereotypes.”

With most of their competition eliminated, the dinosaurs finally took over about 200 million years ago, both herbivores and carnivores.

Cold-adapted plants thrived during this period, allowing the herbaceous dinosaurs to thrive. “The rich vegetation allows herbivores to survive the winter. And that, of course, is food for the carnivores,” explains Olsen.

In the midst of snow and freezing temperatures, dinosaurs caught mammal prey.
Credit: Larry Felder

This discovery could rewrite our understanding of the dominance of dinosaurs in the Jurassic. “I think this research is interesting because it’s another story from another time, one that challenges dinosaur stereotypes,” said Anthony Fiorillo, a paleoecologist at Southern Methodist University who was not involved in the study. “Their isolation mechanism is very interesting,” Fiorillo, who has researched Arctic dinosaurs, told Mashable.

In freezing climates, dinosaurs also likely adapted. Dinosaur growth could have slowed during the colder months of the Arctic compared to the warmer months, Fiorillo explained. Fossilized bones have markings called bone rings, similar to tree rings, which indicate when they temporarily stopped growing. This allows the animal to conserve energy during harsh winters when food sources are dwindling.

Olsen and his team plan to continue to search for strong evidence (ice raft debris) that suggests dinosaurs reproduced in colder climates. Stay tuned: Our understanding of dinosaur rule is still being written.

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