Dinosaurs are often seen as creatures that thrive in hot climates and lush tropical jungles. But now, new research is challenging that idea: Dinosaurs instead endured freezing temperatures, which ultimately allowed them to rule in the Jurassic.
The study’s lead author, paleontologist Paul Olsen, ventured to China’s Junggar Basin in 2016, an area rich in dinosaur fossils and footprints. On day one, and on their very first stop, Olsen’s team came across something much coarser than sand and gravel. This seemed quite unusual for Olsen.
“We didn’t move for three hours discussing what it is,” Olsen, who led the research published in the journal Scientists progresstold Mashable.
“The whole image of dinosaurs is retrograde. They are primarily cold-adapted animals.”
The research team reduced the curious deposits to “glacial debris”, which are sediments containing pebbles that formed around 206 million years ago. (Ice accumulated in water next to land, transporting and eventually dropping land rocks lodged in ice at the bottom of a lake.) Its presence in the region indicates that floating ice once existed in an area where dinosaurs roamed and left clear tracks. The researchers also determined that the Junggar Basin is located above the Arctic Circle, which means it is extremely cold there, especially in winter.
“The whole picture of dinosaurs is retrograde. They’re mostly cold-adapted animals,” Olsen pointed out.
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Dinosaurs first appeared in the Triassic about 230 million years ago when Earth was a single giant landmass called “Pangea”. During the late Triassic, massive volcanic eruptions caused the planet’s temperature to skyrocket. Carbon dioxide levels (which trap heat on Earth) have soared and the oceans have become extremely acidic. These conditions proved inhospitable to most species; the fossil record shows that three out of four terrestrial and oceanic species have disappeared. Yet the dinosaurs somehow survived and then ruled the Jurassic era.
How exactly they succeeded has been a mystery.
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 darkening of the Earth and caused decades-long periods of freezing and plummeting temperatures called “volcanic winters”. Basically, the temperature drops during the violent winter volcanic episodes were much larger than the temperature increase due to carbon dioxide emissions.
Scientists have found glacial sediments in China’s Junggar Basin, a clear sign of cold climates.
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Feather-like adaptation to cope with freezing temperatures
Many unisolated land animals, especially in the tropics, could not adapt to these severe cold spells and became extinct, including a crocodile-like species closely related to dinosaurs. But the dinosaurs survived with a unique adaptation, Olsen said.
Dinosaurs, like birds, were isolated. Similar to the feathers of birds that protect them from the cold, dinosaurs also had a feather-like structure called “protoplumes” which they inherited from their ancestors. (The larger dinosaurs, however, didn’t need feather insulation because they were just gigantic and had high metabolic rates, Olsen told Mashable.)
“I found the study fascinating because it’s another story from another time that challenges the stereotype of dinosaurs.”
With their competition largely eliminated, dinosaurs finally took over about 200 million years ago as both herbivores and carnivores.
Cold-adapted plants thrived during this time, allowing herbaceous dinosaurs to thrive. “The rich vegetation allowed the 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 dinosaur dominance in the Jurassic. “I thought the study was exciting because it’s another story from another time, challenging the stereotype of dinosaurs,” said Anthony Fiorillo, a paleoecologist at Southern Methodist University who didn’t. not participated in the study. “Their isolation mechanism was particularly interesting,” Fiorillo, who studies arctic dinosaurs, told Mashable.
In freezing climates, dinosaurs probably adapted too. Dinosaur growth could have slowed during the cold Arctic months compared to the warmer months, Fiorillo explained. Fossilized bones have marks called bone rings, similar to tree rings, indicating when they have temporarily stopped growing. This allowed the animals to conserve energy during harsh winters when food resources dwindled.
Olsen and his team plan to continue searching for compelling evidence (ice debris) to suggest that dinosaurs thrived in colder climates. Stay tuned: Our understanding of the kingdom of the dinosaurs is still being written.
