Contrary to popular images of dinosaurs roaming a steamy tropical planet, the prehistoric creatures may also have spent long periods living among enormous ice sheets where they evolved feathers to survive the arctic conditions, according to a new study by Chinese and French scientists.
Researchers studying volcanic rocks in northern China found that continental ice sheets might have reached as far south as present-day Hebei province about 124 million years ago, early in the Cretaceous period.
Judging from the deep intrusion by ice melt water in the rock formations, the scientists believe the world then featured an ice-capped landscape, with average annual temperatures as cold as today's polar regions.
Their paper, published online in Nature supports a hypothesis that dinosaurs lived through climate change more volatile than previously thought.
The Cretaceous period has been regarded as one of the earth's hottest eras. Dinosaurs were "greenhouse" creatures living in a tropical environment.
However, Prof. Xu Xing, one of the paper's authors, says the new findings suggest a different scenario. "We had thought the temperature might have dropped as low as it does today in northeastern China, but it turned out to be as cold as the polar regions," says Xu, a researcher with the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences.
Their findings coincide with a drop in global sea levels and a decline in the amount of carbon isotopes — an indicator of organic matter — in Pacific sediments, which also suggested an icy world, Xu says.
"The climate couldn't have been all warm and comfortable for as long as 200 million years for the dinosaurs. They must have gone through some tough times, and those were very likely to include climate change that was far more complex and volatile than our earlier guesses," he says.
"If our findings are correct, the next big question will be how did the dinosaurs survive?"
Feathers may have played a role. Researchers have found many fossils from the Jehol Biota deposit in northern China that show feathers on Cretaceous-era dinosaurs. Today's birds are direct descendants of dinosaurs. But the feathers of that era were too thick for a warm environment.