(ORDO NEWS) — New evidence has emerged that the ancient high latitudes inhabited by early dinosaurs froze regularly, and that these creatures adapted – which apparently became the key to their subsequent dominance.
Many of us know the generally accepted theory of the extinction of the dinosaurs 66 million years ago: Earth‘s fiery impact with a meteorite and the subsequent global winter, when dust and debris choked the atmosphere.
But there was a previous extinction, much more mysterious and less discussed: 202 million years ago, which wiped out the large reptiles that until then ruled the planet and apparently cleared the way for the dinosaurs.
What caused the so-called Triassic-Jurassic extinction event, and why did dinosaurs thrive when other creatures died?
We know that during the pre-extinction Triassic period and the subsequent Jurassic period, which ushered in the age of the dinosaurs, the world was hot and hot.
However, a new study turns the notion of heat-loving dinosaurs on its head: It provides the first physical evidence that Triassic dinosaur species – at the time a minor group mostly relegated to the polar regions – regularly tolerated freezing conditions.
Telling Signs: Dinosaur footprints along with strange rock fragments that could only have been deposited by ice.
The authors of the study believe that during the extinction, colds already occurring at the poles spread to lower latitudes, killing cold-blooded reptiles. Dinosaurs, already adapted, survived and spread. The rest is ancient history.
“Dinosaurs in the Triassic were in the shadows all the time,” says Paul Olsen, a geologist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the study.
“The key to their ultimate dominance was very simple. They were fundamentally cold-adapted animals. When it got cold everywhere, they were ready, but other animals were not.”
Against the background of a lava flow in the distance, a primitively feathered theropod dinosaur carries off a mammalian prey during a snowy volcanic winter caused by powerful eruptions during the Triassic-Jurassic extinction event. Dinosaurs survived because they were already adapted to the cold at high latitudes, a new study says.
The study, based on recent excavations in a remote desert in the Junggar Basin in northwest China, has been published in the journal Science Advances.
It is believed that dinosaurs first appeared in the Triassic period in the temperate southern latitudes about 231 million years ago, when most of the planet’s land mass was united into one giant continent, which geologists call Pangea.
Approximately 214 million years ago, they reached the far north. Before the 202 million year mass extinction, the wider tropical and subtropical regions were dominated by reptiles, including relatives of crocodiles and other fearsome creatures.
During the Triassic and for most of the Jurassic, atmospheric carbon dioxide concentrations were 2,000 parts per million or higher five times what they are today so temperatures must have been high.
Then there was no evidence of the existence of polar ice caps, and excavations have shown that deciduous forests grew in the polar regions.
However, some climate models suggest that the high latitudes were cool during some time periods; even with all that CO2, they should have received little sunlight for most of the year, and temperatures should have dropped, at least seasonally. But so far, no one has provided any physical evidence that they froze.
The supercontinent Pangea 202 million years ago, shortly before the Triassic-Jurassic extinction event.
Evidence of early dinosaurs has been found in these areas; most species lived at high latitudes, and the few species closer to the tropics tended to be smaller. The red area at the top is the Junggar Basin, which is now in northwest China. (Olsen et al., Science Advances, 2022)
At the end of the Triassic, in a geologically short period of about a million years, more than three-quarters of all terrestrial and marine species on the planet became extinct, including armored creatures, corals, and all large reptiles.
Some burrowing animals, such as turtles, survived, as did some early mammals. It is not known exactly what happened, but many scientists attribute it to a series of powerful volcanic eruptions that could last for hundreds of years.
Among other things, eruptions could lead to a sharp increase in carbon dioxide levels in the atmosphere, which would cause deadly temperature fluctuations on land, and the ocean waters would become too acidic for many creatures to survive.
The authors of the new study cite a third factor: During the most ferocious phases, the eruptions spewed sulfuric aerosols that deflected so much sunlight that they caused recurring global volcanic winters that exceeded high levels of greenhouse gases.
These winters could last a decade or more; even in the tropics, persistent frosts could be observed. This killed non-isolated reptiles, but cold-adapted, isolated dinosaurs were able to survive, scientists say.
Researchers’ Evidence: Fine-grained sandstones and siltstones deposited on the bottom of shallow ancient lakes in the Dzhungar basin. The deposits were formed 206 million years ago in the Late Triassic, during and after the mass extinction.
At that time, before the restructuring of the land, the basin was located at 71 degrees north latitude, far beyond the Arctic Circle. Footprints found by the authors and others show that dinosaurs lived along the coastline.
Meanwhile, in the lakes themselves, the researchers found a large amount of pebbles up to 1.5 centimeters across among the usually fine sediments. Being far from the visible coastline, the pebbles could not be there. The only plausible explanation for their presence is ice debris (IRD).
A shale cliff in the Junggar Basin in northwest China where scientists have found ice-formed pebbles among other fine-grained deposits. (Paul Olsen)
Briefly, IRD is formed when ice forms on a coastal landmass and engulfs pieces of underlying rock. At some point, the ice becomes immobile and drifts into an adjacent body of water. When it melts, the rocks sink to the bottom, mixing with the usual fine sediments.
Geologists have extensively studied ancient IRDs in the oceans, where they are delivered by glacial icebergs, but rarely in the bottom of lakes; discovery in the Dzhungar basin added to the meager chronicle.
The authors say that the pebbles were most likely collected in winter, when the waters of the lake froze along the pebbly shores. As the weather warmed up, chunks of ice sailed away with the pebble samples in tow and then dropped them.
“This shows that these places regularly froze, and the dinosaurs did just fine,” said study co-author Dennis Kent, a Lamont Doherty geologist.
How did they do it? Evidence has been accumulating since the 1990s that many, if not all, non-aircraft-carrying dinosaurs, including tyrannosaurs, had primitive feathers. If not for flight, some veils may have been used for mating display purposes, but the researchers say their primary purpose was isolation.
There is also strong evidence that, unlike cold-blooded reptiles, many dinosaurs had warm-blooded systems with high metabolisms. Both qualities could help dinosaurs in cold conditions.
“Severe winter periods during volcanic eruptions may have brought low temperatures to the tropics, which is where large, hairless, featherless vertebrates seem to have gone extinct,” says Kent. “While our beautiful feathered friends, acclimatized to cooler temperatures at higher latitudes, did just fine.”
The findings contradict the conventional wisdom about dinosaurs, but some prominent experts say they are convinced.
“There is a stereotype that dinosaurs have always lived in lush tropical jungles, but this new study shows that at higher latitudes it was cold and even covered with ice for part of the year,” said Stephen Brusatte, professor of paleontology and evolution at the University of Edinburgh.
“It so happened that the dinosaurs that lived in high latitudes already had winter coats, [while] many of their competitors from the Triassic period died out.”
Randall Irmis, curator of paleontology at the Utah Museum of Natural History and specialist in early dinosaurs, agrees.
“This is the first detailed evidence from high paleolatitudes, the first evidence of the last 10 million years of the Triassic, and the first evidence of truly icy conditions,” he said. “People used to think it was a time when it was hot and humid all over the globe, but that wasn’t the case.”
Olsen says the next step to better understand this period will be to search for fossils in former polar regions such as the Junggar Basin.
“The fossils are very bad and no one is looking,” he said.
“These rocks are gray and black, and finding fossils in these beds is much more difficult.”
Most paleontologists are drawn to the Late Jurassic where many large skeletons are known to exist. The paleoarctic is practically ignored.”
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