How did the dinosaurs survive the icy ‘apocalypse’?

The story of how the dinosaurs they disappeared 66 million years ago is quite famous: a giant meteor slammed into Earth, and dust and debris ‘choked’ the atmosphere, producing a global winter. But a long time before, specifically 202 million years, There was a lesser-known, but much more mysterious, extinction that wiped out the great reptiles and raised the dinosaurs as great kings of the world.

The specific causes that explain this relief are still not entirely clear. A new study, published in the journal ‘Science Advances‘sheds some light on the matter: the dinosaurs’ adaptation to the cold, among other things because of their feathers, was the key to their survival.

202 million years ago, during the Triassic, and after the great extinction, at the beginning of the period known as the Jurassic, Earth was, in general, a hot and humid place. However, the discovery of footprints next to rock remains that could only have been deposited by ice confirms with physical evidence that Triassic dinosaurs, then a minor group largely relegated to the polar regions, regularly endured extreme conditions. of freezing.

That is why the authors of the study maintain that, during the Triassic-Jurassic Extinction, cold snaps that were already occurring at the poles spread to lower latitudes, killing cold-blooded reptiles. The adapted dinosaurs survived the evolutionary bottleneck and then spread throughout the world.

dinosaurs

“Dinosaurs were in the coldest areas during the Triassic”it states Paul Olsena geologist at Columbia University’s Lamont-Doherty Observatory and lead author of the study. “The key to their eventual dominance was very simple: they were cold-adapted animals. When temperatures dropped around the world, they were ready and other animals were not.”

Dinosaurs are thought to have first appeared during the Triassic Period in southern temperate latitudes about 231 million years ago, when most of the land masses coalesced into a giant continent named Pangea. They then spread to the northern hemisphere about 214 million years ago. At that time, the intermediate tropical and subtropical regions (the largest areas of the planet) were dominated by giant reptiles. But the cold appeared 202 million years ago and changed the entire balance.

During the Triassic and most of the Jurassic, carbon dioxide levels in the atmosphere were five times higher than they are today, making global temperatures much hotter. This is why there is no evidence of polar ice caps during that time, but there is evidence of deciduous forests that grew in the colder regions.

However, some climate models suggest that high latitudes did experience freezing conditions at least during the winter, because despite all that carbon dioxide, those places received little sunlight for much of the year. But no evidence of these ‘freezing moments’ had been found. Until now.

Extinction at the end of the Triassic

The end of the Triassic, a geologically brief period of perhaps a million years, saw the extinction of more than three-quarters of all terrestrial and marine species on the planet, including creatures with shells, corals, and all reptiles on Earth. considerable size. Some animals that lived in burrows, such as turtles, survived, as did some early mammals. It’s not clear what exactly happened, but many scientists link it to a series of massive volcanic eruptions that lasted hundreds of years.

At this time, Pangea began to break apart, opening up what is now the Atlantic Ocean, and separating what are now the Americas from Europe, Africa, and Asia. Among other things, the eruptions would have caused atmospheric carbon dioxide to skyrocket beyond its already high levels, causing deadly temperature spikes on land and making ocean waters too acidic for many creatures to survive.

The authors of the new study cite a third factor: During the most explosive phases of the eruptions, they would have spewed sulfur aerosols that deflected so much sunlight that they caused repeated global volcanic winters that exceeded high levels of greenhouse gases. These winters could have lasted a decade or more; even the tropics may have seen sustained freezing conditions. This killed the reptiles, adapted to the heat, but the dinosaurs, isolated in colder areas, were able to withstand this climatic ‘apocalypse’.

Tests

The evidence the authors have found in the Junggar Basin in northwest China is fine-grained sandstone and siltstone formations left behind by sediments on shallow ancient lake bottoms. This layer formed 206 million years ago during the late Triassic, and spanned the mass extinction and beyond. At the time, before the landmasses reorganized, the basin lay about 71 degrees north, well above the Arctic Circle.

The footprints found by previous studies show that dinosaurs were present along the coasts. Meanwhile, in the lakes themselves, the researchers found abundant pebbles up to about 1.5 centimeters across within the normally fine sediments. Far from any apparent shoreline, the pebbles didn’t have to be there. The only plausible explanation for their presence is that they were transported by ice.

How does this phenomenon originate?

This phenomenon originates when ice forms against a coastal land mass and incorporates rock fragments from the area. At some point, the ice cracks and moves into the adjoining body of water. When it melts, the rocks fall to the bottom, mixing with normal fine sediments. It is something that has often been seen on the bottom of the oceans, but rarely on the bottom of lakes; the Junggar discovery adds to this meager record.

The authors say the pebbles were likely collected during winter, when the lake waters froze along the pebble-formed shorelines. When the weather got warmer, pieces of that ice floated with remnants of these pebbles, which were transported to the bottom of the lake. “This shows that these areas froze regularly and that the dinosaurs did well.”points Dennis Kent, Lamont-Doherty geologist and co-author of the study.

The key: the feathers of the dinosaurs

Since the 1990s, evidence has been accumulating that many – if not all – non-avian dinosaurs, including tyrannosaurs, they had primitive feathers. It is clear that their function was not flight, so it is believed that the dinosaurs used them to attract the attention of their potential partners during mating. Now researchers point to another possible cause: insulation from the cold. There is also evidence that, unlike cold-blooded reptiles, many dinosaurs were of hot blood. Both of these qualities would have helped dinosaurs in cold conditions.

“Severe winter episodes during volcanic eruptions could bring sub-zero temperatures to the tropics, which is where many of the extinctions of large naked and featherless vertebrates appear to have occurred. Kent says. Whereas feathered dinosaurs, acclimatized to cooler temperatures at higher latitudes, fared better.”.

stereotype about dinosaurs

There is a stereotype that dinosaurs always lived in lush tropical jungles; nevertheless, “This new research shows that higher latitudes would have been frozen and even covered in ice for parts of the year”Explain Stephen Brusatte, professor of palaeontology and evolution at the University of Edinburgh. “It turns out that the dinosaurs that lived in high latitudes already had ‘coats’ to spend the winter, while many of their Triassic competitors did not, and that is why they became extinct”.

Olsen says the next step in understanding this period better is for more researchers to look for fossils in ancient polar areas, such as the Junggar Basin: “The fossil record is very bad and no one is digging in these areas. These rocks are gray and black, which makes it much more difficult to search for these remains in these strata. Most paleontologists are drawn to the Late Jurassic, where many large skeletons are known to exist. The paleo-Arctic is a time quite ignored».

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