Did the dinosaurs have warm blood? Just a little bit.
Some dinosaurs kept their bodies at a higher temperature than the ambient air, without being true homeotherms like birds and mammals. This is the conclusion of researchers who, for the first time, measured the temperature of sauropods and theropods almost directly, by analyzing the eggshell …
How to take the temperature of a dinosaur? Many have tried it for more than a century to answer this question: did they have the warm blood or not? Were they ectotherms like the present reptiles? In this case, their bodies had to take advantage of the heat of the environment, the ambient air or the sun’s rays. Were they not rather endotherms, like the current mammals and especially birds, these cousins of the theropod dinosaurs, a group to which belonged the famous Tyrannosaurus rex? By exploiting their internal heat, endotherms can push their metabolism further and thus resist the cold, run fast or fly.
The study of bone growth, the evaluation of energy expenditure, the analysis of their way of life or the reconstruction of the climates where they lived did not make it possible to decide clearly. And then there is dinosaur and dinosaur. This large family included very different animals and very different sizes.
Well-preserved eggshells of titanosaurs and oviraptorids
A team from UCLA (the University of California at Los Angeles), led by Robert Eagle, used an original method: measuring isotopes of oxygen and carbon in the eggshell and analyzing how 18O and 13C are chemically related. This parameter, explain the researchers, depends on the temperature at which the shell was formed, that is to say, that of the female. The method has been tested previously on several species of reptiles and birds today and had already been used in 2011 on dinosaur teeth.
The team worked on two very different species: a titanosaur found in Argentina and an oviraptorid from Mongolia. The first is a giant, sauropod tens of meters long, walking on all fours. The eggs they worked on are about 80 million years old. The second is a theropod, a group cousin of the present birds, and which already resembled them. Dating indicates an age of 71 to 75 million years.
The delicate method requires well-preserved shells on a chemical level. The researchers retained only three of the six titanosaur eggs, three of the thirteen theropods and zero fossils found in France.
The body of the dinos was 6 ° C warmer than the ambient air
According to the authors, who publish their results in the journal Nature Communications, the temperature of Argentinian titanosaur was 38 ° C, the same value as in the 2011 study of the teeth of an animal of the same group, and that of the Mongolian oviraptor of 32 ° C. But it was hot at that time on Earth, and was not this temperature simply that of the ambient air? To estimate it, the researchers made the same measurements on calcium carbonates drawn from the geological layers of the same regions and dating from the same periods.
Verdict: 6 ° C more inside each of these animals compared to the ambient air. The titanosaur lived in an environment where the temperature reached about 32 ° C and it was rather 26 ° C in what is today Mongolia.
The authors conclude that these dinosaurs were probably not homeotherms but that they were able to maintain a higher temperature in their bodies than the ambient air. Without reaching that of the current birds (often 40 ° C), it should, they explain, allow them to be more active than our current crocodiles and alligators, not so far from the birds but which can provide only brief efforts. Is the old hot-cold blood debate closed?