It is well known how a huge meteorite wiped out the dinosaurs 66 million years ago.
But 202 million years ago, there was a previous extinction that wiped out the large reptiles that had previously ruled the planet, clearing the way for dinosaur takeover.
What led to their flourishing after the so-called Triassic-Jurassic extinction while other creatures went extinct has been much speculation, but a new study claims it has a theory.
He turns the notion of heat-loving dinosaurs on its head by providing the first physical evidence that the Triassic dinosaur species—at that time a small group that lived mostly in the polar regions—were regularly exposed to frost.
The telltale signs were dinosaur footprints, as well as strange rock fragments that could only have been deposited by ice.
Against the backdrop of a lava flow in the distance, a primitively feathered theropod dinosaur is shown claiming a mammal sacrifice during a snowy volcanic winter caused by massive eruptions during the Triassic-Jurassic extinction event. A new study says dinosaurs survived because they were already adapted to the freezing conditions at high latitudes.
The authors of the study, led by Columbia University, say that during the extinction, a cold snap that had already occurred at the poles spread to lower latitudes, killing cold-blooded reptiles.
But because the dinosaurs had already adapted, they survived the evolutionary bottleneck and spread out, leading to their dominance when the world became generally hot and steamy during the Triassic and Jurassic periods.
“During the Triassic period, dinosaurs were constantly under attack,” said 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 essentially cold-adapted animals. When it got cold everywhere, they were ready, but the other animals were not.”
The study was based on recent excavations in the remote desert of the Junggar Basin in northwest China.
Dinosaurs are believed to have first appeared during 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.
They reached the far north about 214 million years ago.
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.
The supercontinent Pangea 202 million years ago, shortly before the Triassic-Jurassic extinction event. Evidence of early dinosaurs has been found in the areas shown. Most species lived at high latitudes, and the few that lived closer to the tropics tended to be smaller. The red area at the top is the Dzungarian Basin, now in northwestern China.
During the Triassic and most of the Jurassic, atmospheric carbon dioxide concentrations were 2,000 ppm or higher, five times today’s levels, so temperatures must have been high.
At that time, 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 cold for a time; even with all that CO2, they would get little sunlight for most of the year, and temperatures would drop, at least seasonally.
But so far, no one has produced any physical evidence that they froze.
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 died out, including armored creatures, corals and all large reptiles.
Some burrowing animals, such as turtles, survived, as did some early mammals.
It’s not clear exactly what happened, but many scientists attribute it to a series of massive volcanic eruptions that could last for hundreds of years on end.
At this time, Pangea began to separate, opening up what is now the Atlantic Ocean and separating what is now the Americas from Europe, Africa, and Asia.
Among other things, the eruptions would cause an explosion of carbon dioxide in the atmosphere above 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 came up with a third factor.
They believe that during the strongest phases of the eruptions, sulfuric aerosols erupted, reflecting so much sunlight that they caused recurring global volcanic winters that quelled 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.
They came up with this theory after discovering fine-grained sandstone and siltstone formations left by sediments on the shallow bottom of ancient lakes in the Dzungarian Basin.
A shale cliff in the Junggar Basin in northwest China, where scientists have found icy pebbles among fine-grained sediments.
The deposits were formed 206 million years ago at the end of the Triassic during the mass extinction and later. At that time, before the land was rebuilt, the basin was at about 71 degrees north latitude, well above the Arctic Circle.
Footprints found by the authors and others show that dinosaurs were present along the coastline.
Meanwhile, in the lakes themselves, researchers found large amounts of pebbles up to about half an inch (1.5 cm) in usually fine sediments.
Away from any visible shoreline, the pebbles had nothing to do there, so the researchers said the only plausible explanation for their presence was ice debris (IRD).
It is created when ice forms on a coastal land mass and includes pieces of underlying rock. At some point, the ice breaks away from the anchor and goes into a nearby body of water.
When the rocks melt, they sink to the bottom, mixing with the usual fine sediments.
Geologists have extensively studied the ancient IRD in the oceans, where it is delivered by glacial icebergs, but rarely at the bottom of lakes. The discovery of the Dzungarian Basin adds to the meager record.
The authors say that the pebbles were probably collected in the winter when the water in the lake froze along the pebble banks.
When the warm weather returned, chunks of this ice sailed away with the pebble samples in tow and later dropped them.
“This shows that these areas regularly froze and the dinosaurs were fine,” said study co-author Dennis Kent, a Lamont Doherty geologist.
Since the 1990s, evidence has been accumulating that many, if not all, non-avian dinosaurs, including tyrannosaurs, had primitive feathers that researchers say were used to insulation.
There is also evidence that, unlike cold-blooded reptiles, many dinosaurs had warm-blooded systems with high metabolisms. Both qualities would have helped them in cold conditions.
“Severe winter periods during volcanic eruptions may have resulted in sub-zero temperatures in the tropics, where large, naked, non-feathered vertebrates appear to have gone extinct,” Kent said.
“While our beautiful feathered friends, who adapted to cooler temperatures at higher latitudes, did just fine.”
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 fossil record is very bad and no one is doing exploration,” he said. “These stones are gray and black and much harder to find. [for fossils] in these layers.
“Most paleontologists are drawn to the Late Jurassic, where many large skeletons are known to be found. The Paleoarctic is largely ignored.”
Research published in the journal Scientific achievements.
DINOSAUR MURDER: HOW A CITY-SIZE ASTEROID DESTROYED 75 PERCENT OF ALL SPECIES OF ANIMALS AND PLANTS
About 66 million years ago, the non-avian dinosaurs were wiped out, and more than half of the world’s species were wiped out.
This mass extinction paved the way for the emergence of mammals and the emergence of humans.
The asteroid Chicxulub is often cited as a potential cause of the Cretaceous-Paleogene extinction event.
The asteroid crashed into shallow water in what is now the Gulf of Mexico.
The impact created a huge cloud of dust and soot that caused global climate change and wiped out 75 percent of all animal and plant species.
The researchers argue that the soot needed for such a global catastrophe could only come from a direct impact on rocks in the shallow waters around Mexico, which are especially rich in hydrocarbons.
According to experts, within 10 hours after the strike, a powerful tsunami wave swept along the Gulf of Mexico coast.
About 66 million years ago, the non-avian dinosaurs were wiped out, and more than half of the world’s species were wiped out. The asteroid Chicxulub is often cited as a potential cause of the Cretaceous-Paleogene extinction event (file image)
This caused earthquakes and landslides in areas such as Argentina.
When investigating this event, researchers found small particles of stone and other debris that was thrown into the air when the asteroid fell.
These small particles, called globules, have covered the planet in a thick layer of soot.
Experts explain that the loss of sunlight led to the complete collapse of the water system.
This is because the phytoplankton base of almost all aquatic food chains would be destroyed.
It is believed that more than 180 million years of evolution, which brought the world to the Cretaceous period, were wiped out in less than the lifespan of a Tyrannosaurus rex, which is 20 to 30 years.