A new study says it has provided the first physical evidence that Triassic dinosaurs withstood regular freezing temperatures, allowing them to survive and eventually replace other species on the planet.
The study, published in the journal Science Advances on July 1, looks at the circumstances surrounding the Triassic-Jurassic Extinction 202 million years ago, which killed a number of large reptiles and led to the eventual takeover of dinosaurs.
During the extinction, researchers say cold snaps killed many cold-blooded reptiles.
Studying footprints and rock fragments in a remote desert of the Junggar Basin in northwestern China, the researchers say Triassic dinosaurs, a relatively small group that inhabit Earth’s polar regions, survived the “evolutionary bottleneck” and have spread.
“Dinosaurs were under the radar all along during the Triassic,” Paul Olsen, a geologist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the study, said in a statement.
“The key to their eventual dominance was very simple. They were essentially cold-adapted animals. When it got cold everywhere, they were ready and other animals were not.”
Dinosaurs are thought to have first appeared about 231 million years ago during the Triassic at temperate southern latitudes, the researchers say.
At that time, most of the Earth’s land had merged into one gigantic continent known as Pangea.
Dinosaurs reached the extreme north about 214 million years ago, and until the mass extinction, reptiles dominated the tropical and subtropical regions of the planet.
While atmospheric concentrations of carbon dioxide were then at or above 2,000 parts per million, or five times current levels, resulting in “intense” temperatures, the researchers say climate models suggest higher latitudes experienced seasonal temperature drops and low for much of the year. would have received sunlight.
By the end of the Triassic, the researchers say massive volcanic eruptions lasting possibly hundreds of years killed more than three-quarters of all life on Earth and in the sea on the planet.
The eruptions would also have caused carbon dioxide levels in the atmosphere to rise, causing deadly temperature spikes and making ocean waters too acidic for many life forms.
But the researchers say the eruptions would also have released sulfur aerosols, able to bend sunlight and trigger repeated “global volcanic winters” lasting a decade and possibly longer.
Not only were Triassic dinosaurs able to survive under these conditions, the researchers say evidence has shown that many, if not all, non-avian dinosaurs also had primitive feathers that would have been used primarily as insulation. Many dinosaurs are also believed to have been warm-blooded and had a high metabolism.
“There’s a stereotype that dinosaurs have always lived in lush tropical jungles, but this new research shows that the higher latitudes would be frozen and even covered in ice for parts of the year,” Stephen Brusatte, a professor of paleontology and evolution at the University of Edinburgh, said.
“Dinosaurs living in high latitudes happened to already have winter coats on [while] many of their Triassic competitors died out.”
As for the physical evidence supporting their study, the researchers looked at fine-grained sandstone and siltstone formations left behind in the sediments of shallow ancient lake beds in the Junggar Basin, formed 206 million years ago during the Late Triassic. At the time, the basin would have been located above the Arctic Circle.
Footprints show dinosaurs were present along the shorelines, while pebbles about 1.5 inches wide found far from any apparent shoreline provided evidence of “ice-ragged debris,” they say.
Ice raft debris forms when ice builds up against a coastal landmass and takes in bits of underlying rock, the researchers say.
The ice eventually loosens and floats away. When it melts, the rocks fall off and mix with the sediment.
The researchers say the pebbles were likely picked up during the winter when the lake water froze and drifted away as the weather warmed.
“This shows that these areas froze regularly, and the dinosaurs did just fine,” said study co-author Dennis Kent, a geologist at Lamont-Doherty.
The researchers say more work is needed to find fossils in former polar regions, such as the Junggar Basin.