The classic image of gigantic dinosaurs living in a hot and steamy prehistoric jungle isn’t wrong — but it is incomplete.

Paleontologists digging in China have found dinosaur tracks alongside evidence of ancient ice. This new evidence contributes to a long-standing debate about whether dinosaurs could have survived freezing temperatures and whether Earth ever fell below freezing during the Late Triassic and early Jurassic. In a paper published Friday in the peer-reviewed journal Science Advances, paleontologist Paul E. Olsen and colleagues draw on recent fieldwork to argue that dinosaurs could — and did — survive low temperatures.

Olsen told IE it’s “a total misconception” that all dinosaurs lived in a hot, prehistoric forest. “Dinosaurs [living] in high latitudes and in polar regions — in places [where] it’s freezing in the winter times — is not marginal. That’s what they did,” he says.

New evidence supports a chilly Triassic

The new evidence comes in the form of what researchers call “lake ice-rafted debris.” When a lake freezes in the winter, ice that forms on the shore picks up large grains of sediment. “When spring comes and the ice breaks up, chunks of ice carrying coarse grains from the shoreline drift out to the middle and drop down,” Olsen says. As sediment accumulates over time, those large grains are sealed in place. It’s a powerful method for researchers trying to understand ancient climates because ice-rafting is the only way for large grains to be transported.

“There’s no hydrodynamic way to get those big grains out in the middle of the lake unless they were rafted out there,” Olsen says. While the sediment analysis was the group’s “fundamental discovery,” they found something else, too: dinosaur footprints. “So, we know dinosaurs were living in that era,” he says.

Proof is mounting that dinosaurs were furry

This is hardly the first evidence that dinosaurs lived in very cold climates. Olsen says many paleontologists have been slow to accept the mounting body of evidence that many (if not all) types of dinosaurs had insulation like feathers or hair-like structures on their bodies. Scientists first documented a dinosaur with filaments (a specialist term for hair-like structures or proto-feathers) in the 1830s, “but everybody ignored that work,” Olsen says.

That specimen was a flying dinosaur that belonged to the order Pterosaur. “Since then, every pterosaur that’s been properly looked at has these filaments,” he says. And it’s not just pterosaurs. Ten years ago, researchers also working in China reported Yutyrannus, which means “feathered tyrant.” It got the name from similar filaments. 

Were all dinosaurs covered in filaments?

In the new paper, Olsen and his co-authors use their new lake sediment data to make the case that all dinosaurs had these filaments on their bodies. “Since pterosaurs are close relatives of dinosaurs, and these filaments are present in pterosaurs and dinosaurs, the simplest argument you can make in terms of the origin of these structures [is that] the common ancestor of pterosaurs and dinosaurs had the filaments,” Olsen said. “The purpose of these filaments is clearly insulation.”

Why is Olsen so sure these structures were for insulation rather than flight? He says it comes down to where they’re found on the body: everywhere. “In pterosaurs, it’s a covering like fur all over their bodies,” he says. He points to something else, too: all kinds of dinosaurs sported the filaments, not just those that could fly. 

There’s no doubt that Earth was much warmer during the Late Triassic and early Jurassic than it is today. This new study shows that the ancient Earth — like the planet today — was very different in different places. 

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