How To Accurately Measure A Dinosaur's Body Temperature

One of the 150 million year old Camarasaurus teeth
from the Morrison Formation , North America, used
 by the Caltech researchers

One of the greatest debates in palaeontological history is  whether dinosaurs were cold or warm blooded. Their reptilian ancestry suggests they were cold blooded. Yet their size indicates they could have just as easily been warm blooded. Palaeontologists have, over the years, come up with theories and evidence to support solutions to the conundrum. Yet despite decades of research, no definitive solution has been presented.

A team of palaeontologists, led by John Eiler from the California Institute of Technology, believe that they have found a way to accurately take the temperature of a dinosaur by using oxygen isotope ratios in the fossil remains. While the process of analysing such ratios has been around for at least a decade, it had never been used for this kind of research. The team took 11, 150 million year old, Brachiosaurus and Camarasaurus teeth from Tanzania, Wyoming and Oklahoma.

Despite the teeth being damaged, they were still able to remove 100 milligram amounts of the enamel for analysis. As the enamel is the hardest part of the body and is replenished on a regular basis, it is very useful in studying the lifestyle of dinosaurs as it provides a long lasting and reliable weekly record of their activities. In fact a similar study using isotope ratios within the enamel of similar creatures proved that giant plant-eating dinosaurs migrated vast distances on a seasonal basis.

After grinding the enamel into a fine powder, a mass spectrometer was used to examine the levels of the oxygen-18 and oxygen-16 isotopes and the way they had clumped together within the teeth. The question is how does this allow scientists to calculate the body temperatures of dinosaurs? This answer to this lies in the way temperature affects the concentrations of specific isotopes. As oxygen-18 is heavier than the more abundant oxygen-16 by two neutrons, it requires more energy to evaporate when dissolved in water.

Higher temperatures mean there will be a higher concentration of oxygen-18. By examining the ratio to oxygen-16, the team was able to calculate the body temperatures of the various dinosaurs to within 2 degrees Celsius. The Brachiosaurus specimens had an average temperature of 38.2 degrees Celsius and the Camarasaurus 35.7 degrees Celsius. It turns out that the creatures were warmer than reptiles, but still cooler than their avian descendants.

While this does not necessarily mean that they were warm blooded, it does provide strong evidence to indicate that they were very different to any other reptiles that walked the Earth. 'What our study resolved is that at least some dinosaurs were physically 'warm', and so — in the simplest sense — were warm-blooded. But we need more information to tell how they were warm-blooded — whether through carefully controlled endothermy, like mammals and modern birds, or through some other physiological strategy, like the 'gigantothermy' used by some large ectothermic animals. We are actively working on the measurements of smaller dinosaurs that will resolve this issue.'