Dinosaurs not cold after all

Thursday, June 23, 2011

The findings, based on tooth analysis, suggests that gigantic sauropod dinosaurs, including the brachiosaurus, which roamed the Earth 150 million years ago, may have had similar active control over their body temperature to modern warm-blooded species.

This would have profound implications for our understanding of dinosaurs' lifestyle and behaviour, suggesting that they were likely to have been quick and agile rather than lumbering, and would have had a high metabolism requiring a vast intake of food, totalling up to ten times the daily consumption of an elephant.

"Originally, dinosaurs were considered to have been cold-blooded animals because they were reptiles, just like salamanders or crocodiles," said Thomas Tutken, a biochemist from the University of Bonn and co-author of the study.

The latest findings suggest that the Brachiosaurus had a temperature of about 38 celsius, while its relative, the Camarasaurus, was about 36 celsius - 15 celsius warmer than modern crocodiles and alligators and a similar temperature to modern mammals.

The normal human body temperature is 37 celsius. The study, published today in the journal Science, estimated the absolute body temperature of dinosaurs by analysing the composition of their dental enamel, which acts as a sort of "chemical thermometer".

Enamel contains carbonate, a combination of carbon and oxygen, both of which come in heavier and lighter variants called isotopes. Heavy carbon and heavy oxygen are decreasingly likely to bond together to form carbonate as the surrounding environment gets warmer, so measuring the amount of heavy carbonate provides a proxy for temperature.

Applying the technique to the teeth of modern mammals suggests it is accurate to within about 1 celsius.

"This is like being able to stick a thermometer in an animal that has been extinct for 150 million years," said Robert Eagle, of the California Institute of Technology, who led the study.

The researchers analysed 11 teeth dug up in Tanzania, Wyoming, and Oklahoma, that belonged to Brachiosaurus brancai and Camarasaurus.

Previously scientists gauged dinosaur metabolism or body temperatures using more indirect measures, for instance by estimating how fast they ran based on the spacing of dinosaur tracks, or measuring the growth rates of bone. But these various lines of evidence were often in conflict.

"For any position you take, you can easily find counterexamples," said Professor John Eiler, a geochemist at Caltech.

The body temperature of reptiles depends almost entirely on the ambient temperature, meaning that lizards typically have to lie in the sun to warm up enough to be active.

"This is why, after a cold night, the mobility of today's reptiles is very limited," said Dr Tutken.

Warm-blooded animals, by contrast, are able to keep their body temperature constant by burning calories. An active heating and cooling system allows mammals to stay active continuously, but also means they require about ten times as much energy as a lizard would need.

"If genuinely warm-blooded, they would have had to hoover up a vast quantity of vegetation to get enough energy," said Dr John Hutchinson, a biomechanics expert at the Royal Veterinary College. "Even a few of them would have deforested a vast area extremely quickly."

However, the question whether dinosaurswere warm-blooded in the same way as modern mammals has not yet been resolved.

The sauropods' large body volume relative to their skin surface area means that body heat loss through their skin would have been slow. Another possibility is that the dinosaurs' huge size made them ideally adapted to keeping a stable, warm temperature, a phenomenon known as gigantothermy.

For more information related to dinosaurs, visit rareresource.com.


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