When we talk about the dinosaurs, their demise is quickly mentioned by a meteorite impact. We never talk about the period in which they did manage to survive, while almost all other species perished.
How the dinosaurs became extinct 66 million years ago is well known to many people: a gigantic meteorite 12 kilometers across crashed in what is now Mexico. A devastating shock wave destroyed everything in its path. The whole world was on fire and the atmosphere filled with dust and soot. Due to a lack of sunlight, the planet was shrouded in darkness. A long, cold and dark period followed in which many plant and animal species became extinct. The dinosaurs also found their Waterloo in this way.
The Triassic Jurassic Extinction
But there has been a mass extinction of species on Earth much earlier. Much less research has been done on this mysterious Triassic-Jurassic extinction 202 million years ago, when the Triassic transitioned into the Jurassic period. We know that both the Triassic and Jurassic periods have generally been very warm and humid eras. But that wasn’t the case everywhere: Excavations at the Junggar Basin in northwestern China show that dinosaurs were regularly exposed to sub-zero temperatures during the Triassic. At that time, this area was at latitude 71 degrees north.
Insignificant animal species
Dinosaurs were only found above the Arctic Circle at the time, and it was only an insignificant group on Earth. Giant crocodiles and other reptiles ruled the roost. We know about the existence of the Arctic dinosaurs because footprints have been found in rock fragments that must have been formed by ice deposits. The researchers think that during the mass extinction there were increasingly longer ice periods, first only at the poles, but later also around the equator. As a result, the cold-blooded reptiles died, while the dinosaurs had already adapted to the cold in the Arctic regions. After the mass extinction, they were able to spread further over the earth and the 135 million year long age of the dinosaurs began.
Below the radar
“During the Triassic, dinosaurs were constantly moving under the radar,” says geologist Paul Olsen van Columbia University† “The key to their success in the Jurassic period was very simple. They were very well prepared for cold temperatures. When it started to freeze everywhere, they were all set. Other animals were taken by surprise,” explains the lead author, whose study was recently published in the professional journal Science Advances popped up.
The idea is that dinosaurs first walked the Earth about 231 million years ago, somewhere in the Southern Hemisphere. There was only one continent then: Pangea. The dinosaurs arrived in the far north about 17 million years later, where they adapted to the colder climate. Until 202 million years ago, the rest of the world was the domain of crocodiles, reptiles and other prehistoric beasts.
Hot and humid
In the Triassic and a large part of the Jurassic, the CO2 concentrations were five times as high as today. It was very hot and humid, probably there were no polar ice caps. Excavations show that there were dense forests above the Arctic Circles. However, climate models also show that at times it was very cool in the polar regions. At the end of the Triassic comes a ‘short’ time of no more than a million years, during which more than three quarters of all land and sea animals become extinct. Some turtle species survive, along with some mammals. And the dinosaurs.
It is unclear what exactly happened. Many scientists attribute the extinction to highly active volcanic periods, which could last as long as a hundred years. The primordial continent of Pangea broke into pieces and our present continents slowly drifted apart. All these volcanic eruptions resulted in an even higher concentration of CO2 in the air. Temperatures on earth continued to rise and the acidity of the oceans became too much for many marine plants and animals.
sulfur gas
But Olsen and his team come up with a new theory: In the most violent phases of the eruptions, so much sulfur gas would have been sprayed into the air that hardly any sunlight could reach the surface of the earth. This caused volcanic ice winters that could last ten years or more.
It may even freeze in the tropics. A disaster for the cold-blooded reptiles, but a blessing for the warm-blooded dinosaurs. According to the scientists, they were already prepared for the cold because of their warm fur and feathers. Evidence for this theory of the rise of the dinosaurs has been found in the aforementioned Chinese excavations. The composition of rock formations in the basin, dating to 206 million years ago, can only be explained by drifting ice. In addition, dinosaur footprints from the same period have been found on the beach. “You can conclude from this that this area regularly froze over. The dinosaurs coped well with this,” says co-author and geologist Dennis Kent.
feathered friends
“The severe winter spells that followed the massive volcanic eruptions may have cooled the tropics for several years in a row. Many of the large, naked and featherless species have been destroyed by this,” Kent said. “Our feathered friends, on the other hand, were already used to the winter conditions because of their past in the polar regions. They survived the freezing cold.”
Randall Irmis, curator of paleontology and expert on early dinosaurs, agrees. “This is the first clear evidence of dinosaurs above the Arctic Circle in icy conditions during the latter period of the Triassic. People always think that the whole world was humid and warm back then, but this shows that this was not the case.”
Difficult to find
Project leader Olsen hopes that more attention will be paid to fossils in former polar regions, such as the Junggar basin. “The fossil record is poor, no one is looking,” he explains. The rocks there are gray and black, it’s very hard to find fossils under those conditions. Most paleontologists focus on the late Jurassic. It’s a lot easier to find a large skeleton from that period. Hardly anyone is interested in the prehistoric Arctic.”
While it is precisely these finds that can turn our whole picture of the dinosaurs and their survival mechanisms upside down.
Source material:
†Dinosaurs took over amid ice, not warmth” – Science Advances
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