TORONTO - Fossils of a tropical fresh water Asian turtle that surfaced in Arctic Canada suggest they migrated to North America not around Alaska but directly across a freshwater sea floating atop the warm, salty Arctic Ocean.
The finding also suggests that a rapid influx of carbon dioxide some 90 million years ago was the likely cause of a super-greenhouse effect that created extraordinary polar heat.
‘We’ve known there’s been an interchange of animals between Asia and North America in the late Cretaceous period, but this is the first example we have of a fossil in the High Arctic region showing how this migration may have taken place,’ said John Tarduno, professor of geophysics at the University of Rochester, who lead the expedition.
In 2006, Tarduno led an expedition to the Arctic to study paleomagnetism - the Earth’s magnetic field in the distant past. Knowing from previous expeditions to the area that the rocks were rich with fossils, Tarduno kept an eye out for them and was rewarded when one of his undergraduate students uncovered the amazingly well preserved shell of a turtle.
Together with collaborator Donald Brinkman of the Royal Tyrrell Museum of Canada, they later named the fossil Aurorachelys, or aurora turtle. The turtle strongly resembles a freshwater Mongolian species, which raised obvious questions about how it came to be in the marine waters of the North American Arctic, said a Rochester release.
At the time the aurora turtle lived, the Arctic Ocean was probably even more separated from the global oceanic circulation system than it is today. Numerous rivers from the adjacent continents would have poured fresh water into the ancient Arctic sea.
Since fresh water is lighter than marine water, Tarduno thinks it may have rested on top of the salty ocean water, allowing a freshwater animal such as the aurora turtle to migrate with relative ease.
These findings were published in Geology.