A new study has offered what it says is the first physical evidence to show that Triassic period dinosaurs regularly endured freezing conditions, allowing them to survive and eventually replace other species on the planet.
The study, published in the journal Progress of science on July 1, discusses the circumstances surrounding the Triassic-Jurassic Extinction 202 million years ago, which wiped out a number of large reptiles and led to the eventual dominance of the dinosaurs.
During the extinction event, researchers say cold snaps killed many cold-blooded reptiles.
Through the study of footprints and rock fragments in a remote desert of the Junggar Basin in northwestern China, researchers say that Triassic dinosaurs, a relatively minor group that populate Earth’s polar regions, survived the “neck of evolutionary bottle and dispersed”.
“Dinosaurs were there during the Triassic under the radar all along,” 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 fundamentally cold-adapted animals. When it was 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 period in southern temperate latitudes, the researchers say.
At that time, most of the land on Earth was united into one giant continent known as Pangea.
Dinosaurs arrived in the far north about 214 million years ago and until the mass extinction, reptiles dominated the tropical and subtropical regions of the planet.
While atmospheric carbon dioxide concentrations back then were 2,000 parts per million or more, or five times today’s levels, resulting in “intense” temperatures, the researchers say climate models suggest higher latitudes they experienced seasonal temperature drops and would have received little sunlight much of the year. .
At the end of the Triassic period, researchers say massive volcanic eruptions that could last hundreds of years killed more than three-quarters of all land and marine 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, but the researchers say evidence has shown that many, if not all, non-avian dinosaurs also had primitive feathers that would have been used primarily for insulation. It is also believed that many dinosaurs were warm-blooded and had high metabolisms.
“There’s a stereotype that dinosaurs always lived in lush rainforests, but this new research shows that higher latitudes would have been frozen and even covered in ice for parts of the year,” said Stephen Brusatte, professor of paleontology and evolution at the University of Edinburgh said.
“It turns out that dinosaurs living in high latitudes already have winter coats [while] many of its Triassic competitors became extinct.”
As for the physical evidence supporting their study, the researchers looked at fine-grained sandstone and siltstone formations left behind in the sediments of ancient shallow lake bottoms in the Junggar Basin, formed 206 million years ago during the Triassic. late. At that time, the basin would have been located above the Arctic Circle.
The footprints show that dinosaurs were present along shorelines, while pebbles about 1.5 centimeters wide, found far from any apparent shoreline, offered evidence of “ice-entrained debris,” they say.
Ice-entrained debris forms when ice builds up against a coastal landmass and absorbs chunks of underlying rock, the researchers say.
The ice eventually breaks off and moves away. As it melts, the rocks break off and mix with the sediment.
The researchers say the pebbles were likely collected during the winter when the lake waters froze and floated away as the climate warmed.
“This shows that these areas froze regularly and that the dinosaurs did well,” said study co-author Dennis Kent, a geologist at Lamont-Doherty.
The researchers say more work is needed to find fossils in ancient polar areas, such as the Junggar Basin.