Dinosaurs are often thought of as creatures that thrive in warm climates and lush tropical jungles. But now new research challenges that idea: Rather, dinosaurs endured sub-freezing temperatures, which ultimately allowed them to reign in the Jurassic.
The study’s lead author, paleontologist Paul Olsen, ventured into China’s Junggar Basin in 2016, a region rich in dinosaur fossils and footprints. On day one, and at their very first stop, Olsen’s team encountered something much coarser than sand and gravel. That struck Olsen as quite unusual.
“We didn’t move for three hours arguing about what that is,” Olsen, who led the research published in the journal scientific advancessaid Mashable.
“The whole picture of dinosaurs is backward. They are primarily cold-adapted animals.”
The research team narrowed down the curious deposits to “ice-rafted debris,” which are sediments with pebbles that formed about 206 million years ago. (Ice accumulated in water adjacent to land and eventually transported earth rocks stuck in the ice and dropped them onto a lake bed.) Its presence in the region indicates that floating ice once existed in a region where dinosaurs roamed and left clear tracks. The researchers also noted that the Junggar Basin was above the Arctic Circle, meaning it was extremely cold there, especially in winter.
“The whole picture of dinosaurs is backward. They are primarily cold-adapted animals,” emphasized Olsen.
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Dinosaurs first appeared in the Triassic about 230 million years ago when the earth was a single giant landmass called “Pangaea”. At the end of the Triassic, massive volcanic eruptions caused the planet’s temperature to skyrocket. Carbon dioxide levels (which trap heat on Earth) skyrocketed and the oceans became extremely acidic. These conditions proved inhospitable to most species; The fossil record shows that three out of four land and ocean species are extinct. But the dinosaurs somehow survived and then dominated the Jurassic period.
Exactly how they managed to do this was a mystery.
But Olsen’s study now offers an explanation: The same volcanic eruptions that spewed vast amounts of heat-trapping carbon dioxide into the atmosphere also released the chemical sulfur dioxide, which blocks sunlight.
This triggered a darkening of the Earth, causing decades of periods of falling, freezing temperatures called “volcanic winters.” Crucially, the temperature drops during severe volcanic winters were far greater than the temperature increases from carbon dioxide emissions.
Scientists found ice-blown sediments in China’s Junggar Basin, a clear sign of cold climates.
Credit: Paul Olsen
Feather-like adaptation to freezing temperatures
Many non-isolated terrestrial animals, particularly in the tropics, failed to adapt to these severe cold snaps and became extinct, including a crocodile-like species closely related to dinosaurs. But the dinosaurs survived with a unique adaptation, Olsen said.
Dinosaurs were isolated like birds. Similar to bird feathers that protect them from the cold, dinosaurs also had a feather-like structure called “protofeathers” that they inherited from their ancestors. (The largest dinosaurs didn’t need featherweight insulation, however, since they were simply gigantic and had high metabolic rates, Olsen told Mashable.)
“I found the study exciting because it’s a different story from a different time that challenges the dinosaur stereotype.”
After their competition was largely eliminated, dinosaurs, both herbivores and carnivores, finally took over about 200 million years ago.
During this time, cold-adapted plants thrived and herbaceous dinosaurs thrived. “The lush vegetation allowed herbivores to survive the winters. And of course that was food for the carnivores,” explained Olsen.
In the midst of snow and freezing temperatures, a dinosaur catches prey from mammals.
Credit: Larry Fields
The discovery could rewrite our understanding of dinosaur dominance in the Jurassic. “I found the study exciting because it’s a different story from a different time that challenges the dinosaur stereotype,” said Anthony Fiorillo, a paleoecologist at Southern Methodist University who was not involved with the study. “Their isolation mechanism was particularly interesting,” Fiorillo, who studies arctic dinosaurs, told Mashable.
Dinosaurs are also likely to have adapted to frigid climates. Dinosaur growth may 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, that indicate when they’ve temporarily stopped growing. This allowed the animals to conserve energy during severe winters when food resources dwindled.
Olsen and his team plan to continue searching for compelling evidence (ice raft debris) that suggests dinosaurs thrived in colder climes. Stay tuned: Our understanding of dinosaur rule is still being written.