• When a giant meteorite hit Earth 65 million years ago, wiping out the dinosaur reign, they were already in decline, according to a study.

  • Dinosaurs would have been hit hard by falling temperatures.

  • The first disappearances concerned herbivores, causing an imbalance of the entire ecosystem.

    Especially carnivores, which devour them.

When a meteorite hit Earth 65 million years ago, wiping out the dinosaur reign, these large reptiles were already in a bad way.

For 10 million years, they were even already on the decline.

This is the conclusion of a study, published Tuesday in the journal

Nature Communications,

conducted by Fabien Condamine, CNRS researcher at the Institute of Evolutionary Sciences in Montpellier (Hérault).

Particularly valuable results, for those interested in dinosaurs: paleontologists bicker over whether their extinction happened suddenly, or if the 12 km2 meteorite only dealt "the coup de grace", notes the researcher. , to an already well-worn group.

Fabien Condamine leans for the second hypothesis.

Falling temperatures

“Their decline would be due to major changes in the environment, including temperature drops during the Cretaceous,” he underlines. We would have lost 7 ° C, at the very least. For these species, unable to produce their own body heat, and which need high temperatures to feed, move or reproduce, this climate change would have been disastrous. “This drop in temperatures correlates with an increase in the extinction” of dinosaurs, continues Fabien Condamine.

To make matters worse, the first disappearances first concerned herbivores, leading to an imbalance of ecosystems.

And, in particular, a gradual extinction of the wicked carnivores, who found fewer and fewer herbivores to eat.

“If we make an analogy with today, with the African plains, for example, all herbivores, giraffes, elephants, zebras, wildebeest or gazelles are very structuring for the entire ecosystem, explains the Montpellier researcher. .

Because all predators depend on them.

But also parasites, and plants.

Without the elephants, there is no longer the same vegetation.

"

"A lesson" for the man whose "environment is deteriorating"

To achieve these results, the international team led by Fabien Condamine analyzed the evolution during the Cretaceous period of six large families of dinosaurs, including the famous tyrannosaurs, triceratops and hadrosaurs.

Researchers have accumulated heaps of fossil data over several years, and have estimated the evolution of each species over the millennia.

Our dossier on dinosaurs

For Fabien Condamine, this study highlights “a good example of a hyper-dominant group” which, faced with external disturbances, is gradually declining.

“We can compare that to other dominant groups,” says the researcher.

I am thinking in particular of certain groups of sharks, which today find themselves on the verge of extinction.

And to the man?

"It's a lesson for us, too, that's for sure," he notes.

Our environment is deteriorating.

Climatically speaking, moreover.

"

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