Widespread volcanic eruptions around 202 million years ago had a significant impact on Earth’s climate, triggering a mass extinction event that wiped out three-quarters of the planet’s species, including many large reptiles. Dinosaurs, on the other hand, survived and thrived.
Dinosaurs are frequently thought to be heat-loving creatures, perfectly suited to the steamy greenhouse environment of the Triassic Period. But, unlike other reptiles of the time, their ability to adapt to cold temperatures may have been the key to their survival. Researchers report in Science Advances that the dinosaurs’ warm feather coats may have helped the creatures weather relatively brief but intense bouts of volcanic winter associated with the massive eruptions.
“We’ve known for a while that there were probably volcanic winters” associated with the massive eruptions, says paleontologist Paul Olsen of the Lamont-Doherty Earth Observatory at Columbia University. Along with carbon dioxide, volcanoes spew sulfur particles into the atmosphere that can darken skies for years and lower global temperatures — as the Philippines’ Mount Pinatubo did after its powerful 1991 eruption. “But how [such winters] fit into the picture of the end-Triassic mass extinction has been very unclear.”
Olsen and his colleagues present the first physical evidence that such winters occurred at the end of the Triassic, as well as that dinosaurs were present to weather them. The team discovered rock fragments that could only have been deposited by ancient ice alongside dinosaur footprints at a site called the Junggar Basin, which was discovered near the end of the Triassic period high in the Arctic Circle.
There’s a popular misconception that dinosaurs always lived in lush tropical jungles. But this new research shows convincingly that the higher latitudes would have been freezing and even covered in ice during parts of the year at the beginning of the rise of the dinosaurs.
Stephen Brusatte
“There’s a popular misconception that dinosaurs always lived in lush tropical jungles,” says Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved in the new study. “But this new research shows convincingly that the higher latitudes would have been freezing and even covered in ice during parts of the year” at the beginning of the rise of the dinosaurs, he says.
The Triassic Period ended with a bang beginning around 202 million years ago, as the supercontinent Pangea began to break apart. Massive volcanic eruptions burst forth as the crust split, opening up a basin that became the Atlantic Ocean. The hardened lava from those eruptions now spans 7 million square kilometers across Africa, Europe, and North and South America, forming a rock sequence collectively known as the Central Atlantic Magmatic Province, or CAMP.
Carbon dioxide levels were extremely high during the late Triassic and early Jurassic periods, with many of those levels now thought to have been pumped into the atmosphere by volcanic eruptions. As a result, Earth is thought to have been in a steamy greenhouse state. This hypothesis is supported by the lack of evidence of polar ice sheets at the time; instead, thick forests extended all the way to the poles.
The Junggar Basin in what is now northwestern China was one such area, with coniferous and deciduous forests growing alongside a massive ancient lake. Dinosaurs were undoubtedly present: No bones have yet been discovered at the site, but many footprints of the creatures are preserved in the shallow-water siltstones and sandstones that formed at the bottom of the lake.
The new data suggest that — despite the extremely high CO2 levels — this region also experienced harsh, frigid winters, with the lake at least partially freezing over. The evidence comes from the same rocks that bear the footprints. Analyzing the distribution of grain sizes in the rocks, the researchers determined that a large portion of the grains weren’t part of the original lake mud, but had been carried there from elsewhere.
The most likely explanation, Olsen says, is that these grains are “ice-rafted debris” — a well-known phenomenon in which bits of rock freeze to the base of ice along a shoreline, and then hitch a ride with the ice as it eventually drifts into open water. As the floating ice melts, the bits of rock sink, deposited in new territory.
Volcanic winters could last tens or hundreds of years, according to Olsen, depending on how long volcanoes continue to erupt. In this case, the massive lava sheets associated with the CAMP eruptions point to at least tens of thousands of years of eruption pulses, if not a million. That could have kept the winters going for a long time — long enough to wipe out many less-well-insulated reptiles, he adds. The team believes that episodes of freezing temperatures may have extended all the way to the tropics.
Evidence of feathers has been found in the fossils of many types of dinosaurs, from carnivorous theropods to herbivorous ornithischians. Recent reports that flying reptiles called pterosaurs had feathers too now suggests that the insulating fuzz has been around for even longer than once thought — possibly appearing as early as 250 million years ago, in a common ancestor of dinosaurs and pterosaurs.
Thanks to those insulating feathers, dinosaurs were able to survive the lengthy winters that ensued during the end-Triassic mass extinction, Olsen and colleagues say. Dinosaurs might then have been able to spread rapidly during the Jurassic, occupying niches left vacant by less hardy reptiles.
This study “shows the complexity of disentangling not only the success of certain groups, but also the causes and effects of mass extinction events,” says paleontologist Randall Irmis of the University of Utah in Salt Lake City, who was not connected with the study. “There’s a pretty good consensus that [the CAMP eruptions are] the cause of the mass extinction — but there are a lot of subtleties we haven’t appreciated.”
Irmis believes that dinosaurs living in the far north at the time were able to survive due to their feathery insulation. But it’s unclear whether a volcanic winter caused by dimming could have extended far enough south to freeze the tropics as well, giving dinosaurs a similar advantage there. “Dimming is a global effect, but how it manifests itself is much more severe at the poles than at low latitudes.”
According to Irmis, feathers are likely just one of many reasons dinosaurs diversified and spread rapidly across the globe at the start of the Jurassic period. “A lot goes into why they became such a successful group.”
