A new study has offered what it says is the first physical evidence showing that dinosaurs from the Triassic period regularly endured freezing conditions, allowing them to survive and eventually replace other species on the planet.
The study, published in the journal Science Advances on July 1, examines the circumstances surrounding the Triassic-Jurassic extinction event 202 million years ago, which killed off a number of large reptiles and led to the takeover possible dinosaurs.
During the extinction event, researchers say the cold snaps killed many cold-blooded reptiles.
By studying footprints and rock fragments in a remote desert in the Junggar Basin in northwest China, researchers say that Triassic dinosaurs, a relatively minor group inhabiting Earth’s polar regions, survived the “evolutionary bottleneck and expanded”.
“The dinosaurs were there during the Triassic under the radar all the time,” said Paul Olsen, geologist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the study, in a statement.
“The key to their eventual dominance was very simple. They were basically cold-adapted animals. When it was cold everywhere, they were ready, and other animals weren’t.”
Dinosaurs are believed to have first appeared around 231 million years ago during the Triassic period in southern temperate latitudes, researchers say.
Back then, most of the land on Earth was united into one giant continent known as Pangea.
The dinosaurs reached the far north around 214 million years ago and until the mass extinction, reptiles dominated the tropical and subtropical regions of the planet.
While atmospheric carbon dioxide concentrations then were 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 have experienced seasonal temperature drops and would have received little sunlight for much of the year. .
At the end of the Triassic period, researchers say massive volcanic eruptions lasting hundreds of years killed more than three-quarters of all land and sea life on the planet.
The eruptions would also have caused carbon dioxide levels in the atmosphere to rise, creating 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, capable of deflecting sunlight and causing repeated “global volcanic winters” lasting a decade and possibly longer.
Not only were Triassic dinosaurs able to survive in 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 possessed high metabolisms.
“There is a stereotype that dinosaurs have always lived in lush tropical jungles, but this new research shows that higher latitudes would have been freezing and even covered in ice during some parts of the year,” said Stephen Brusatte, professor of paleontology and evolution at the university. University of Edinburgh, said.
“It turns out that dinosaurs living at high latitudes already had winter coats [while] many of their Triassic competitors died out.”
As for the physical evidence supporting their study, the researchers examined fine-grained sandstone and siltstone formations left in the sediments of ancient shallow lake bottoms in the Junggar Basin, formed 206 years ago. million years at the end of the 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 centimeters wide, found far from any apparent shoreline, provided evidence of ‘ice debris’, they say .
According to the researchers, ice debris forms when ice piles up against a coastal landmass and absorbs pieces of underlying rock.
The ice eventually breaks off and moves away. As the rocks melt, they fall and mix with the sediments.
The researchers say the pebbles were likely picked up during the winter when the waters of the lake froze and floated as the weather warmed.
“It shows that these areas were freezing regularly and the dinosaurs were doing very well,” said study co-author Dennis Kent, a geologist at Lamont-Doherty.
Researchers say more work is needed to find fossils in ancient polar areas, such as the Junggar Basin.