Around 200 million years ago, a mass extinction event on the Earth killed off many of the reptile species that ruled the planet, ushering in the era of the dinosaurs.
Exactly how this event, known as the Triassic-Jurassic Extinction, occurred has remained somewhat of a mystery. But now, a study carried out at by a team of international researchers suggests that the dinosaurs’ domination of the Earth could be in part due to their ability to survive freezing temperatures.
During the Triassic Period, which stretched from roughly 250 million years ago to 200 million years ago, the environment on the Earth was largely hot and steamy. At this time most of the planet’s land was joined together in a supercontinent known as Pangaea. Back then, the balmy tropical and subtropical regions were dominated by reptiles, including the relatives of modern-day crocodiles.
Dinosaurs are thought to have first appeared around this time in the temperate southern regions of the Earth. But somewhere around 214 million years ago they began to migrate north as Pangea began to separate and form the continents we see today.
In this time of intense tectonic activity, massive volcanic eruptions began to belch out huge quantities of carbon dioxide, creating deadly temperatures on land, and turning ocean waters far too acidic for many of the Earth’s inhabitants to survive.
However, the fiercest of these eruptions would have thrown out huge amounts of sulphur into the atmosphere. Previous studies have shown that this phenomenon could have deflected so much sunlight that it led to regular volcanic winters.
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Now, new evidence based on recent excavations in the remote desert of northwest China’s Junggar Basin suggests that the decade-long periods of cold caused by these seismic events could have spread across the globe, killing off cold-blooded animals such as reptiles and paved the way for the warm-blooded, feather-insulated dinosaurs to thrive.
“Dinosaurs were there during the Triassic under the radar all the time,” said lead author Prof Paul Olsen, a geologist based at Columbia University’s Lamont-Doherty Earth Observatory.
“The key to their eventual dominance was very simple. They were fundamentally cold-adapted animals. When it got cold everywhere, they were ready, and other animals weren’t.”
The team came to the conclusion after finding footprints of dinosaurs in the Junggar basin along with pebbles scattered along the shoreline that were likely carried there by drifting ice rafts – an indication that the area was subject to periods of freezing and thawing.
“Severe wintry 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 co-author Dr Dennis Kent, a geologist based at Lamont-Doherty.
“Whereas our fine feathered friends acclimated to colder temperatures in higher latitudes did OK.”
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