Most dinosaurs were warm-blooded

Most dinosaurs were warm-blooded, like birds and mammals, rather than cold-blooded like reptiles, a study revealed Wednesday that provides the first direct measure of their metabolism.

It is based on a new technique measuring the metabolic rate of dinosaurs, that is to say their greater or lesser capacity to convert oxygen into energy to live, according to scientists led by paleobiologist Jasmina Wiemann, from California. Institute of Technology.

Warm-blooded animals, such as birds or humans, have a high metabolism. They absorb a lot of oxygen, necessary for the production of calories allowing them to maintain their temperature and remain active.

Conversely, cold-blooded ones, such as reptiles, have more moderate activity and depend on external conditions to maintain their body temperature. In short, they don’t bask in the sun for pleasure, but out of necessity.

This dichotomy has posed a problem for dinosaur naturalists. Because one of their descendants, the birds, are warm-blooded, while their closest cousins ​​at the time, like the crocodiles, were cold-blooded reptiles.

So much so that a resounding study from 2014 even attributed to dinosaurs a system… with warm blood. But always by estimating their metabolism by indirect and unreliable methods, taking into account the temperature of formation of minerals in their bones or their rate of bone growth.

The study published in Nature looks at the key element of metabolism, the use of oxygen, and more specifically the study of its traces in the form of “leftovers” in the bones.

“It leaves a record of how much oxygen a dinosaur breathed, and therefore its rate of metabolism,” Jasmina Wiemann said in a statement.

His team applied this non-destructive method, based on infrared spectroscopy, to the femurs of 55 groups of animals, including dinosaurs, to measure “the molecular markers (of the remains) which are linked to the metabolic rate”. , according to the researcher.

Result: in the two large groups of dinosaurs, that of the ornithischians had cold-blooded specimens, such as the triceratops, with its large collar and two imposing horns, or the stegosaurus, with its backbone. Massive but slow-moving herbivores.

On the other hand, the other group, that of the saurischians, the most numerous in terms of species and especially of descent, was essentially warm-blooded. With giant herbivores, such as sauropods, and iconic carnivores, such as the Tyrannosaurus, or the aptly named Velociraptor, popularized by the film Jurassic Park.

This group is most famous for being home to all the lineages of birds, the only descendants of the dinosaurs to survive the great extinction of species that occurred 65 million years ago.

It was believed that the warm blood and high metabolism of the birds had enabled them to survive this disaster, due to the climatic upheaval caused by a gigantic meteorite.

In the case of dinosaurs, warm blood did not protect them from it, the study notes.

“We are experiencing a sixth species extinction,” Wiemann said, “so it is important to understand how current and extinct animals have responded to previous climate change and environmental disruption.” To better understand the future challenges of biodiversity.

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