Dinosaurs may have outsurvived other creatures living alongside them during a largescale extinction preceding the period where they became dominant due to their ability to survive in frosty conditions, according to a new peer-reviewed study published in Science Advances on Friday.
The period in which the dinosaurs were dominant was preceded, just as it ended, by a largescale extinction called the Triassic-Jurassic Extinction.
In general, the world was hot and steamy during the Triassic Period, when dinosaurs first showed up as a small group of species that stayed mostly in the polar regions, as high levels of carbon dioxide filled the atmosphere.
Up until recently, it was largely believed that the polar regions were warm as well, with forests growing there and no evidence of ice caps. Some climate models have suggested that the high latitudes were chilly sometimes, but no physical evidence for this had been found, up until now.
The Triassic period ended with extinction that killed off more than three-quarters of all terrestrial and marine species on the planet. What exactly caused the extinction is unclear, but scientists have connected it to a series of massive volcanic eruptions that may have lasted hundreds of years, as Pangea (the giant single continent) began to split apart into the continents we know today.
The eruptions would have caused the already high carbon dioxide levels in the atmosphere to rise substantially, causing severe temperature hikes and making ocean waters too acid for many creatures to survive.
Global winters brought dinosaurs to the top
But according to the authors, the eruptions caused another phenomenon, bursting sulfur aerosols into the air that deflected so much sunlight that it caused global volcanic winters that may have lasted over a decade.
These winters killed uninsulated reptiles, but the dinosaurs, insulated and adapted to the cold, were able to survive, according to the study.
The scientists found fine-grained sandstone and siltstone formations left by sediments in shallow ancient lake bottoms in the Junngar Basin formed 206 million years ago during the Late Triassic Period. At that time, the basin sat well above the Arctic Circle.
The scientists and others found footprints that show that dinosaurs were present along the shorelines of the ancient lakes. In the lakes themselves, the researchers found abundant pebbles up to about 1.5 centimeters across within the normally fine sediments far from where they should have been found.
According to the scientists, the pebbles were ice-rafted debris (IRD), which is created when ice forms against a coastal landmass and incorporates bits of the underlying rock. At some point, the ice becomes unmoored and drifts away in the adjoining water body. When it melts, the rocks drop to the bottom, mixing with the normal sediments.
While geologists have studied ancient IRD in the oceans, they rarely have studied them in lake beds. The pebbles found in the basin show “these areas froze regularly, and the dinosaurs did just fine,” said study co-author Dennis Kent, a geologist at Lamont-Doherty, in a news story on the website of the Columbia Climate School.
Feathery insulation, high metabolism helped dinosaurs stay warm
The authors of the study pointed to evidence that many dinosaurs had feathers, which they say may have been used for insulation. The dinosaurs also may have possessed warm-blooded, high-metabolism systems. These two qualities could have helped them survive chilly conditions.
“Severe wintery episodes during volcanic eruptions may have brought freezing temperatures to the tropics, which is where many of the extinctions of big, naked, unfeathered vertebrates seem to have occurred,” said Kent. “Whereas our fine feathered friends acclimated to colder temperatures in higher latitudes did OK.”
“There is a stereotype that dinosaurs always lived in lush tropical jungles, but this new research shows that the higher latitudes would have been freezing and even covered in ice during parts of the year,” said Stephen Brusatte, a professor of paleontology and evolution at the University of Edinburgh. “Dinosaurs living at high latitudes just so happened to already have winter coats [while] many of their Triassic competitors died out.”
Dinosaurs living at high latitudes just so happened to already have winter coats [while] many of their Triassic competitors died out.”
Stephen Brusatte, a professor of paleontology and evolution at the University of Edinburgh
According to Paul Olsen, a geologist at Columbia University’s Lamont-Doherty Earth Observatory, and the lead author of the study, the next step to better understand this period is for more researchers to look for fossils in areas that used to be in the poles.
“The fossil record is very bad, and no one is prospecting,” he said. “These rocks are gray and black, and it is much harder to prospect [for fossils] in these strata. Most paleontologists are attracted to the late Jurassic, where it’s known there are many big skeletons to be had. The paleo-Arctic is basically ignored.”