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Scientists Take Dinosaur’s Temperature

June 24, 2011

Scientists have found a way to take the temperature of dinosaurs that have been extinct for millions of years.

But since you cannot take their temperature like you do with humans, the researchers did the next best thing — study dinosaur teeth, which can reflect body temperature.

What they found is surprising.

Studying the teeth of the long-necked Brachiosaurus, they discovered it had a temperature of about 100.8 degrees F and the smaller Camarasaurus had a temp of 98.3 degrees. Humans average about 98.6.

The study, published in the online edition of the journal Science on Thursday, will not soon settle the long-theorized belief that dinosaurs are cold-blooded, however. The mainstream belief is that most all dinosaurs require outside sources of warmth to maintain movement, much like lizards of today do.

When dinosaurs were first discovered in the 19th century, paleontologists thought the massive beasts needed sunlight and warmth from the surrounding environment to keep agile. But research over the past few decades suggests that they were much faster and more nimble creatures, requiring body temperatures like mammals.

In cooperation with colleagues from the US California Institute of Technology (Caltech), researchers from the University of Bonn in Germany have just determined that the body temperatures of some large herbivorous dinosaurs were warm-blooded after all.

“Our analysis really allows us rule out that they could have been cold, like crocodiles, for example,” lead researcher Robert A. Eagle of the California Institute of Technology said in a briefing.

But, he added, “this doesn’t necessarily mean these large dinosaurs had high metabolism like mammals and birds … they could have been `gigantotherms’ and stay warm because they were so large.”

A giant body mass is very good at keeping temperatures constant, explained co-author Thomas Tuetken of the University of Bonn.

The teams’ research was on sauropods, the largest of the dinosaurs, and researchers explained that animals that large can retain body heat even with a relatively low metabolism, simply because they are so big. Brachiosaurus was a massive 40 tons, while Camarasaurus weighed in at 15 tons.

The Caltech team developed the new approach to measure dinosaur temps through their teeth, providing them with new insights into whether these huge beasts were cold or warm blooded. They measured the isotopic concentrations in the teeth and found that these dinosaurs were as warm as most modern mammals.

“This is like being able to stick a thermometer in an animal that has been extinct for 150 million years,” said Robert Eagle, a postdoctoral scholar at Caltech and lead author on the paper to be published online in the June 23 issue of Science Express.

“Nobody has used this approach to look at dinosaur body temperatures before, so our study provides a completely different angle on the longstanding debate about dinosaur physiology,” Eagle says.

“The consensus was that no one would ever measure dinosaur body temperatures, that it’s impossible to do,” added John Eiler, a coauthor and the Robert P. Sharp Professor of Geology and professor of geochemistry. And yet, using a technique pioneered in Eiler’s lab, the team did just that.

The finding “confirms that dinosaurs were not sluggish, cold-blooded animals,” commented Roger Seymour of the University of Adelaide, Australia, who was not involved in the new research. But “the debate about dinosaur metabolic rate will go on, no doubt, because it can never be measured directly and paleoscientists will often seek evidence to support a particular view and ignore contrary evidence,” he added.

Geoffrey F. Birchard of George Mason University in Fairfax, VA, agreed that the debate is likely to continue.

The findings confirm what the temperatures of these beasts were, but knowing what the temperature was in something so big doesn’t necessarily confirm it was a warm-blooded creature, Birchard told the Associated Press. Birchard was not part of the new research.

Aradhna Tripati, a coauthor of the study who is an assistant professor at UCLA and visiting researcher in geochemistry at Caltech, said: “The body temperatures we’ve estimated now provide a key piece of data that any model of dinosaur physiology has to be able to explain.”

“As a result, the data can help scientists test physiological models to explain how these organisms lived,” he added.

The measured temperatures are lower than what is predicted by some models of body temperatures, suggesting there is something missing in science understanding of dinosaur physiology. The models imply dinosaurs were gigantotherms and maintained warm temps by their sheer size. To explain lower temperatures, the researchers suggest that the dinosaurs could have had some physiological or behavioral adaptations that allowed them to avoid getting too hot.

The dinosaurs could have had lower metabolic rates to reduce the amount of internal heat, particularly as large adults. They could also have had something like an air-sac system to dissipate heat. Alternatively, they could have dispelled heat through their long necks and tails, researchers said.

Previously, researchers had to rely on indirect ways to gauge dinosaur metabolism or body temperatures. Examples of these earlier measurements including using dinosaur behavior and physiology, figuring out how fast they moved based on spacing of dinosaur tracks, studying the ratio of predators to prey in the fossil record, or measuring growth rates in bone. But these various areas of measurements were often debated and conflicts arose.

“For any position you take, you can easily find counterexamples,” said Eiler. “How an organism budgets the energy supply that it gets from food and creates and stores the energy in its muscles””there are no fossil remains for that. So you just sort of have to make your best guess based on indirect arguments,” he said.

The new developments, however, show that it is possible to take body temperatures of dinosaurs, and it leaves guessing out of the equation, Eiler concluded.

The researchers say their next goal is take temperatures of more dinosaur samples from a wider range of specimens and extend the study to other species of extinct vertebrates. Knowing the body temperatures of more dinosaurs and other extinct animals will help scientists learn more about how the physiology of modern animals and birds evolved. 

Image Caption: Skull reconstruction of Camarasaurus; its body temperature was similar to that of humans. Credit: Sauriermuseum Aathal, Switzerland

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