A mass extinction event sparked by a sudden shift in climate more than 200 million years ago reshaped life on Earth and ushered in the age of the dinosaurs, scientists claim.
An international team reviewed geological evidence and the fossil record and found that enormous volcanic eruptions in what is now western Canada coincided with a global loss of plants and animals.
While the crisis 233 million years ago wiped out great segments of life, it set the stage for the dinosaurs to take over, and for some of the first mammals, crocodiles and turtles to extend their ranges.
“There was clearly a mass extinction that we now call the Carnian Pluvial Episode, which was a bit hidden and mystical,” said Mike Benton, a paleontologist at Bristol University. “It brought an opportunity for the dinosaurs, which would have been the obvious things you would see, but also mammals, turtles and others.”
Jacopo Dal Corso, a scientist who worked on the project at Leeds University in England, said that geochemical signatures from the time point to massive volcanic eruptions which pumped vast amounts of greenhouse gas into the air, driving repeated spikes in global warming.
Dal Corso traced them back to the Wrangellia province of western Canada, where Triassic eruptions ejected volcanic basalt that now forms much of the west coast of North America.
The warming climate, and heavier rains it brought, might have helped life at first, but the conditions became extreme and were followed by an extended arid period.
Lush vegetation, such as seed ferns, died off and were replaced with less bountiful conifers. The plants made for slim pickings and many herbivore species crashed, the authors found.
It is unclear why the dinosaurs thrived after the crisis, but the fossil record shows that many species spread into new territories.
Another wave of herbivorous beasts, such as the 4 tonne Plateosaurus, found fresh grounds in what are now Germany, South America and southern Africa.
Some of the oldest crocodile-like creatures began to range far and wide too, with remains found in Argentina, Brazil, North America and India.
Similar evidence was found for beak-headed reptiles and early turtles, according to the researchers, who had funding from the Hanse-Wissenschaftskolleg Institute for Advance Study in Germany.
The mass extinction, which adds to the “big five” recorded over the past 500 million years, hit the oceans hard, wiping out an estimated third of marine life.
The destruction cleared the way for modern coral reefs and groups of plankton as life on Earth reset, the authors write in Science Advances.
Steve Brusatte, a paleontologist at the University of Edinburgh who was not involved in the review, said that there was mounting evidence for “a big spate of environmental and climate changes” about 233 million years ago, which preceded the appearance of dinosaurs in the fossil record.
He said that it was “tempting and exciting” to link the events, but the jury was still out.
“It’s going to come down to that age old issue: Did the climate change cause the dinosaur diversification, or is the timing a coincidence? Ultimately that means the timeline is going to be critical,” he said.
“We’ll see what the next few years bring. The authors have set out an ambitious agenda for testing this big, bold idea that dinosaur diversification was triggered by climate and environmental change. I think the odds are good and I hope it pans out, because what a story it would be,” he said.
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