More than sixty years have passed since we definitively put aside the image we had of dinosaurs as big, slow and dumb lizards, yet there are still aspects of their physiology that are not entirely clear to us – as expected, given that we are talking about animals that have been extinct for millions of years and that we have no way of studying directly.
The most classic example is that of homeothermy, or put another way: were dinosaurs cold-blooded or warm-blooded? The second hypothesis is the most popular one today, as demonstrated by a new study which, for the first time, reconstructs the metabolism of T. rex (or Tyrannosaurus rex if you prefer the full name), one of the most iconic dinosaurs of all time which, as we read above Science Advanceshad a temperature very similar to modern endotherms.
The thermometer in the teeth
How do you study the body temperature of an extinct animal? The team led by Randon Flores of the University of California did it using teeth: three, to be precise, from the Hell Creek Formation in Montana. Two belonged to the same young man T. rexnicknamed Thomas and weighing more than three tons at the waist, while the third came from another individual.
The researchers studied the isotopes of carbon and oxygen stored in the enamel through a technique called clumped isotope paleothermometry: essentially, the way in which some heavy isotopes combine in minerals varies according to the temperature at which the latter were formed, thus transforming the fossil tooth into a kind of thermometer that has remained stationary for about 66 million years.
The average result of this measurement says that the T. rex had a body temperature of 36.3 ± 2.5 °C. To verify that that number did not simply reflect the warm climate of the Cretaceous, the authors also analyzed five teeth of crocodilians that lived in the same environment: their average was 30.9 ± 2.6 °C, significantly lower.
Even climate reconstructions of the region give ambient temperatures lower than those of the T. rexwhich therefore was not hot “because it was hot”: the fossil bivalves of the Hell Creek Formation, which mainly record warm season conditions, indicate an average temperature of around 25.9 °C. The T. rexIn short, it was warmer than both its ectothermic neighbors and the surrounding environment.
The advantages of “warm blood”
The reconstructed temperature is very similar to that of modern elephants, around 36°C, slightly lower than ours and not too far from that of large flightless birds such as ostriches and emus.
It is therefore another clue in favor of the idea that at least some theropod dinosaurs had an endothermic physiology, that is, they were capable of internally producing a good part of the heat necessary to maintain high body temperature.
However, the authors urge caution: a huge animal like T. rex it could also conserve heat thanks to its own mass, through the so-called thermal inertia, and it is not possible to reconstruct its metabolism with certainty from its body temperature alone. Furthermore, the study is based on just three teeth belonging to two individuals.
However, that internal heat could have had very concrete consequences on the life of the T. rex. Using the estimated temperature to build a model of its climate niche, the researchers found that much of Late Cretaceous North America could have been suitable for T. rexincluding relatively cold areas located at high latitudes.
The known fossils would therefore represent only a part of the potentially available range: a large predator capable of keeping itself warm would not have needed to limit itself to the milder regions of the continent.
