Ancient turtle rode 'freshwater wave' to migrate from Asia to North America
Washington, Feb 2 (ANI): In a new research, scientists have found a surprise fossil of a tropical, freshwater, Asian turtle in Arctic Canada, which suggests that the ancient animal migrated from Asia to North America directly across a freshwater sea floating atop the warm, salty Arctic Ocean.
The find, by a team of geologists from the University of Rochester in the US, rebuffs an earlier theory that said animals migrated from Asia to North America around Alaska.
"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 and leader of the Arctic expedition.
The finding also suggests that a rapid influx of carbon dioxide (CO2) some 90 million years ago was the likely cause of a super-greenhouse effect that created extraordinary polar heat.
"We're talking about extremely warm, ice-free conditions in the Arctic region, allowing migrations across the pole," said Tarduno.
In 2006, Tarduno led an expedition to the Arctic to study paleomagnetism, which incidentally led to the discovery of the 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.
Tarduno's paleomagnetic expertise, which allows him to ascertain when points on Earth's crust were at specific locations, allows him to rule out the possibility that millions of years of tectonic activity had brought the fossil from southern climes.
The turtle was clearly a native of the area.
As to how a freshwater turtle migrated across a salty ocean; Tarduno points to the results of drilling by the Integrated Ocean Drilling Program's ACEX expedition that demonstrated episodes of unusually fresh surface waters in the past Arctic Ocean.
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. (ANI)