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Giant turtles built for comfort, not speed.

Giant turtles built for comfort, not speed

It's not easy to measure the metabolism of a 1,000-pound turtle. But three researchers who took pains to do so have characterized a mechanism that allows these large reptiles, traditionally considered "cold-blooded," to stay warm in chilly environs. Their findings support the controversial proposition that cold-blooded dinosaurs could have lived comfortably in the Cretaceous Arctic, about 100 million years ago.

Frank V. Paladino of Purdue University at Fort Wayne, Ind., working with Michael P. O'Connor and James R. Spotila of Drexel University in Philadelphia, studied the leatherback turtle, Dermochelys coriacea, one of today's largest reptiles. Biologists classify turtles as ectothermic, or unable to adjust their body temperatures significantly using metabolic reactions. But somehow, leatherbacks range from the tropics to the Arctic and can maintain internal temperatures of 25 [degrees]C in 7[degrees]C seawater.

The researchers put respirators over the snouts of six leatherbacks, then suspended the animals in tripod-supported hammocks for a few hours before measuring oxygen consumption rates. They also measured these rates in active, nesting leatherbacks and used mathematical models to predict heat-exchange rates through turtle tissues and blood. The bottom line, they report in the April 26 NATURE, is that although leatherbacks feature metabolic rates far lower than those in mammals, their insulating bulk lets them retain heat efficiently in cold environs. (In warm climes, they note, leatherbacks apparently enhance heat loss by increasing blood flow to their extremities.) The researchers suggest a new term for large reptiles' use of body mass to stay warm in the cold: gigantothermy.

Fossils verify that dinosaurs spent time in the Arctic, but scientists remain divided over whether these huge reptiles simply migrated through the region -- which was cold in the winters but not permanently frozen -- or lived there year-round. Paladino says gigantothermy could have allowed dinosaurs to survive the chilly climate even without the high metabolic rates or hyperactive behaviors that others have proposed.
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Author:Weiss, R.
Publication:Science News
Date:Apr 28, 1990
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