Giant four-legged dinosaurs were not cold-blooded as previously thought, but had body temperatures similar to those of present-day birds and mammals, a study has found.
But scientists are still trying to work out how they kept cool.

The findings, based on studies of fossilised dinosaur teeth, lend support to the idea that dinosaurs were warm-blooded creatures which regulated their body warmth.

Cold-blooded lizards, snakes and crocodiles lack this ability and their temperature rises and falls according to ambient conditions.

As a result, modern reptiles slow down when the weather is cold and become more active when it is warm.

However, the new research does not settle the argument over dinosaur metabolism.
Animals as large as some of the biggest sauropod dinosaurs would be expected to retain heat because of the insulating effect of their huge bodies.

In fact, they should have been warmer than the tooth findings suggest. This suggests they had an as-yet-undiscovered method of cooling down, perhaps by lowering their metabolic rate or dissipating heat through air sacs in their bodies.

The research, reported in the journal Science, involved analysing 11 teeth from Brachiosaurus and Camarasaurus, two giant sauropods that lived more than 150million years ago.

Mineral formation in tooth enamel is influenced by temperature. By measuring relative levels of carbon and oxygen isotopes - different versions of the same element - in the enamel, the scientists could work out the dinosaurs' body temperature to within one or two degrees Celsius.

They found that Brachiosaurus had a temperature of around 38.2C (100.8F) and Camarasaurus of about 35.7C (96.3F).

'This is like being able to stick a thermometer in an animal that has been extinct for 150million years,' said lead researcher Dr Robert Eagle, from the California Institute of Technology.
'Nobody has used this approach to look at dinosaur body temperature before, so our study provides a completely different angle on the long-standing debate about dinosaur physiology.'
When dinosaurs were first discovered, experts assumed they were cold-blooded like other reptiles.

But research in the last few decades suggests many of them might have been warm-blooded and nimble, like the velociraptors depicted in the Jurassic Park films.

The scientists now want to calculate the temperature of smaller dinosaurs less able to retain heat.
If they also had high body temperatures, it would clearly indicate that they were warm-blooded.