Paleontology has been immersed in a profound debate for many years: were the dinosaurs warm-blooded or cold-blooded? Why is this question important? Knowing whether dinosaurs were cold-blooded or warm-blooded could give us clues about how active they were and what their daily lives were like. Now, a team of scientists from the California Institute of Technology (USA) believes they have found the final answer. What is the solution to the dilemma? That varies between species.
Cold blooded or warm blooded?
Thus, predatory dinosaurs like Velociraptor and Tyrannosaurus rex had very high metabolic rates and were probably warm blooded and others like Stegeosaurus or Triceratops , were like reptiles, cold blooded.
“This is really exciting for us as paleontologists: the question of whether dinosaurs were warm-blooded or cold-blooded is one of the oldest questions in paleontology, and we now think we have a consensus that most dinosaurs were warm-blooded. hot”. explains Jasmina Wiemann, lead author of the article published in the journal Nature.
“The new proxy developed by Jasmina Wiemann allows us to directly infer metabolism in extinct organisms , something we only dreamed of a few years ago. We also found different metabolic rates characterizing different groups, which was previously suggested based on other methods.” , but never tested directly,” says Matteo Fabbri, a postdoctoral researcher at the Field Museum in Chicago and one of the paper’s authors.
The importance of metabolism
In essence, metabolism is the way an organism effectively converts oxygen into chemical energy or fuels for the body. Animals with high metabolic rates are endothermic or warm-blooded. For example, birds and mammals need a lot of oxygen and use a lot of calories to keep their bodies warm (it’s part of the reason marine mammals need to come to the surface to breathe). On the other hand, exothermic or cold-blooded animals like reptiles, breathe less and eat less with their lifestyle, which is less energetic than warm-blooded animals. That also means that they depend on the outside world to keep their bodies warm.
And how have they managed to determine this data?
Taking a dinosaur’s temperature would have been an activity – apart from impossible – quite risky during the Cretaceous, but researchers have managed to estimate the body heat of many known species. They found that if they could identify how much oxygen the dinosaurs were consuming, they would have a pretty good indication of how warm they were staying ; a much more reliable method than checking the isotope ratios in your bones, among others.
The team analyzed the femurs of 55 different groups of animals , including dinosaurs, pterosaurs, plesiosaurs, modern birds, mammals, and lizards. They compared the amount of molecular byproducts related to respiration to known metabolic rates in living animals. These data were then used to infer the metabolic rates of the extinct animals. Dinosaurs can be divided into two main groups: the saurischians (reptile hips) and the ornithischians (bird hips). The results of the study suggest that these two groups had very different metabolic rates.
warm blooded dinosaurs
Velociraptor, Tyrannosaurus rex, and Brachiosaurus , all had high metabolic rates and were probably warm-blooded.
cold blooded dinosaurs
Triceratops and Stegosaurus had low metabolic rates and were probably cold-blooded.
“Giant warm-blooded sauropods were herbivores and a lot of plant matter would be needed to fuel this metabolic system,” the authors explained. “They had very efficient digestive systems, and since they were so large, it was probably more of a problem for them to get cold than warm.”
“Reconstructing the biology and physiology of extinct animals is one of the most difficult things to do in paleontology. This new study adds a critical piece of the puzzle to understanding the evolution of physiology in deep time and complements previous proxies used to To investigate these questions, you can now infer body temperature through isotopes, growth strategies through osteohistology , and metabolic rates through chemical proxies.”
Reference: Wiemann, J., Menéndez, I., Crawford, JM et al. Fossil biomolecules reveal an avian metabolism in the ancestral dinosaur. Nature, 2022 DOI: 10.1038/s41586-022-04770-6