Scientists have discovered a tropical Asian turtle fossil not in Asia or in the tropics, but high in the Canadian Arctic.
The find supports the view that, tens of millions of years ago, the Arctic was much warmer then than it is now. The fossil also suggests that Asian turtles took advantage of those balmy conditions to migrate across the North Pole on a land bridge that was filled with lakes and rivers.
Previously, scientists thought turtles made the trek at lower latitudes.
"It is generally thought that a land bridge through Alaska helped bring Asian fauna across into North America, but that doesn't really explain how you get turtles on the east coast of North America at the same time as on the west," said University of Rochester geologist Rory Cottrell, one of the authors of the new study, which appeared last month in the journal Geology.
"One major significance to come out of this find is that there may have been another way."
An expedition team from the University of Rochester found the fossil in 2006 on Axel Heiberg Island in the High Canadian Arctic. Rock deposits on the island are full of vertebrate fossils, including turtles, crocodile reptiles, fish and "all sorts of other weird things," Cottrell said.
The turtle fossil was a particularly exciting because it was a nearly complete mold of both the top and bottom of the animal's shell. And the shell was big, measuring 30 centimeters (almost a foot) across. The animal belonged to a group called Macrobaenidae. The researchers nicknamed it Hugo.
Turtles are fair-weather creatures, and the icy Arctic today is way too cold to support them. Hugo, however, lived about 95 million years ago during a warm period called the Cretaceous. The era is often used as an example of what a greenhouse Earth would be like.
Even the Arctic was balmy at the time, with average temperatures hovering around 14 degrees Celsius (57 degrees Fahrenheit), said Don Brinkman, a paleontologist at the Royal Tyrrell Museum in Alberta, Canada, who helped analyze the turtle. The region would have felt like modern-day North Carolina. The fact that Hugo lived there helps show was happening at the poles at the time — and what could happen with future climate change.
"It gives us some idea of how dramatic the effect of temperature change was on biota in the past," Brinkman said. "There's no reason to think it would be any different today."
Hugo also helps fill in some blanks in what we know about the history of turtles on Earth, said Robert McCord, Curator of Paleontology at the Arizona Museum of Natural History, in Mesa. The fossil doesn't just suggest a new route for ancient migrations of Asian turtles. It also pushes the date of those migrations back more than 10 million years.
After a slow pace of discovery, several exciting papers have been published in recent months about ancient turtles, McCord added. "It's wild stuff all of a sudden in the turtle field."