University of Colorado researchers have conducted a study that explains how ancient alligators and giant tortoises were able to thrive on Ellesmere Island well above the Arctic Circle, despite six months of darkness each year.

The study has implications for the impacts of future climate change as Arctic temperatures continue to rise, said Professor Jaelyn Eberle.

The team concluded the average temperatures of the warmest month on Ellesmere Island during the early Eocene were from 66 to 68 degrees Fahrenheit (19-20 degrees C), while the coldest month temperature was about 32 to 38 degrees F (0-3.5 degrees C).

"We use the water that the animals were drinking as a proxy for paleotemperature," said Eberle.

The team looked at teeth from a large, hippo-like mammal known as Coryphodon, as well as bones from bowfin fish and shells and bones from aquatic turtles from the Emydidae family, the largest and most diverse family of contemporary pond turtles.

"By looking at a host of animals with different physiologies, we were better able to pin down warm- and cold-month temperatures," she said.

The new study showed that Eocene alligators could withstand slightly cooler winters than their present-day counterparts, although data from captive alligators show they are heartier than other members of the crocodilian family and can survive short intervals of subfreezing temperatures by submerging themselves in the water.

However, the case of large land tortoises is puzzling, since today's large tortoises inhabit places like the Galapagos Islands where the cold-month average temperature is about 50 degrees F (10 degrees C.), said Eberle.

She added that the tortoises' present range in the Americas does not represent their fullest geographic range as allowed by climate. Factors like hunting by early Native Americans and the past extent of glaciers probably are playing a role in today's distribution of giant tortoises, she said.

The new study highlights the impacts of continuing global warming on Arctic plants and animals, Eberle said.

And increasing human activities in the area are causing temperatures in the Arctic to rise twice as fast as those at mid-latitudes as greenhouse gases build up in Earth's atmosphere, according to scientists.

The study was published in this month's issue of Earth and Planetary Science Letters. (ANI)