Tropical Turtle Fossil Gives Clues of the Ancient Arctic Scene

Author:  Dunia Rassy
Institution:  London School of Hygiene and Tropical Medicine

Once, an Asiatic freshwater turtle decided to migrate to an attractively warm paradise called the Arctic. Ninety millions years later, a shivering team, from the University of Rochester found its fossilized shell haphazardly in the same area. The decision of migrating may now prove to be the wisest in the turtle's life, since its fossil is helping us build in our minds what the Arctic used to be like and how the Earth's dynamics have radically transformed the landscape. The findings were published in the February edition of the journal Geology.

The fossil was discovered in 2006 and confirms that many animal species crossed from Asia to North America and vice versa 65 to 165 million years ago. With the help of Donald Brinkman of the Royal Tyrrell Museum of Canada, the team identified the fossil as a relative of the Mongolian freshwater turtle, which made the researchers wonder how the turtle reached the Arctic's salty water. The leader of the project, John Tarduno, ruled out that earthquake-like activity had brought the fossil to the pole. Tarduno then recalled the results of a former ocean drilling expedition showing that there was a superficial layer of fresh water in the ancient Arctic. Rivers most likely supplied the water, and as fresh water is lighter than marine water, the former stayed on top.

While a freshwater superficial layer made the journey more easily, observations have led the scientists to believe that volcano activity created the conditions for tropical species to inhabit the Arctic. The fossil itself was found on top of the last solid lava layers. Volcanoes probably pumped huge amounts of carbon dioxide into the atmosphere in a short time, trapping heat from the sun and bringing about a greenhouse. These eruptions may have also been responsible for creating a chain of underwater islands, which allowed animals to hop from one to another on their way from Asia to northernmost America.

It also appears this is not the first time the Arctic has experienced warming. The problem, as Tarduno stated, is that "it is difficult to separate short-term climate trends (as global warming might be) from a longer term pattern". Consequently, Tarduno wishes to return to the Arctic to unearth more pieces and present us with a much more complete explanation of why the Arctic was once warm. Ideally, this would allow us to understand current weather changes and anticipate the Earth's future climate.

Written by: Dunia Rassy

Edited by: Jeff Kost (News and Features Editor) and Nira Datta (Professional Reviewer)