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Selon les travaux d’une équipe franco-anglo-canadienne, les grands dinosaures herbivores ont commencé à décliner environ 10 millions d’années avant que la météorite qui mènera à leur extinction heurte notre Terre. En cause, une chute brutale des températures. © denissimonov, Adobe Stock

The dinosaurs crashed before the asteroid fell

Dinosaurs. In the collective imagination, they were the undeniable masters of our earth. Until a meteorite arrives to put an abrupt end to their rule. But researchers are now proposing a new reading of the fossil record. They present dinosaurs that had already fallen before the catastrophe. In particular, it involves sudden climate change. Fabian Condamine, a CNRS researcher at the Institute of Evolutionary Science in Montpellier, explains to us how his team came to these conclusions that revive the debate.

66 million years ago, a Meteor More than ten kilometers in diameter illuminated the sky of our earth. She finished her race on her side Peninsula Yucatan of Mexico. Putting an end to the regime Dinosaurs. “Bad times”, Ideas for us Fabian Condamine, CNRS researcher at the Institute of Evolutionary Science in Montpellier. “Because conflict occurs in a world Pressure. The world is experiencing its vegetation, climate and global change Sea level. A world where dinosaurs have not already done their best. “

Anyway, the result of the work he is now doing with a Franco-Anglo-Canadian team. A decision based on facts. Direct evidence from the registry Archeology. Evidence for the existence of certain species at a particular time, in a particular place. From that the researchers estimated the training rate or ratioExtinction of species. Thanks for the sophisticated method of Modeling Was able to limit the dependencies associated with the gaps in the register in the statistic. However, “With the knowledge that is constantly accumulating, we are not free from the different conclusions that will come in the next few years. This is also science.”, Fabian points out the condomine.

But, in the meantime, let’s come to this glorious conclusion. Because it still has something to wonder about. Because until then, it was generally accepted, in the end Cretaceous, Dinosaur groups are very prolific. They diversified and found solutions to fill different spaces. However, researchers today suggest the opposite.

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“We have identified the peak of diversity in dinosaurs – or at least, of the six large families targeted by the study – They were extinct at least 10 million years ago. Between this peak and the meteorite fall on the Yucatan Peninsula, we saw a significant decline in species diversity. – Understand, the number of organisms, Fabian Condomine explains. We were looking to shed light on the diversification dynamics of dinosaurs. We don’t think about the decline. It seemed to us in the data. “

A layered phenomenon of destruction

So once this decline is taken – if science can take anything at such a stage … -, the researchers chose to follow an integrated approach, including a dozen possible causes. Among them, the so-called causes abiotic, Related to the environment Physics In which dinosaurs evolved Temperature, Sea level or continental fragment. “Because at that time, our planet underwent a lot of tectonic changes.” Researchers have also studied so-called biological causes. Thus, changes observed at the level of plants.

“This is the moment when flowering plants take over the cones”, Find us Fabian condomine. The inherent diversity of dinosaurs is another possible biological cause. “Specific diversity for a group affects the diversity of species. We’re talking about diversity bias. As group diversification, opportunities to create a species are less likely to fill key spaces. The group finds fewer solutions to fill new spaces.

Finally, as researchers emerge from their work, two factors strongly influence this processExtinction of species. Is the first Global warming It decreases drastically over time. About 7 C. One would have thought that dinosaurs and the mesothermal animals they inhabit would be slightly affected. However, “We notice that dinosaurs are finally significantly dependent on the temperature of their environment.”, Fabian mentions the condomine.

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Another sign of the decline 10 million years before the extinction of the dinosaurs: the decline of dinosaur diversity Plant species. “It simply came to our notice then. Large plant species have the structure of an organism Ecosystem. Unclosures or trichotillomania played a major role in the Cretaceous ecosystem. As this species began to decline, due to its greater sensitivity to temperature changes, other plant species followed, followed by carnivorous foods. This is a layered erosion event that appears in the data. “

However the researcher is wary of these results. Because when we separate Vegetables and meat dishes, “Data loses its statistical power”. To confirm all of this, it is therefore necessary to expand the study to more dinosaurs. “We worked in only six families. Most known. Groups fromSouthern Hemisphere, But the records are less detailed. We should also be interested in titanosers – These are one of the largest animals ever to occur on our planet. They might tell us a slightly different story. “ However, the debate seems to have resumed …

Want dinosaurs to disappear?

The most accurate estimate of the origin and extinction rates of dinosaur species millions of years before the Cretaceous-tertiary crisis reveals that these spectacular animals have fallen. One can speculate that sooner or later they will inevitably lead to mammals.

Article Laurent Sacco Posted on 04/20/2016

For decades, hypotheses about the disappearance of one of the most successful groups of animals in the evolution of organisms have been widespread: Dinosaurs. From poisonous plants to mammals devouring eggs, overcoming climate change caused by sea recedes, almost everything happened. These are ultimately the hypotheses of an explosion Deccan traps And the impact of a celestial bodyAstronomy From சிக்க்சலப் It came to the center in the early nineties.

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However, an article was published Pnas By a group Biologists The picture is complicated. They used the pile of data found in the Earth’s geological records and, thanks to sophisticated techniques of statistical analysis, were able to estimate the rate of emergence of new organisms and their disappearance in the previous 50 million years. The famous Cretaceous-tertiary crisis, which occurred about 66 million years ago.

Surprisingly, the symptoms senescence Appeared, because the total balance shows a steady decrease in diversity Dinosaur species, Further marked in the case Plant species Long neck. So something already weakened these animals and drove them out Biosphere, Even though we still do not know what it is. Explosions Basaltic The impact of a celestial body may have already been dangerous to them because they had already fallen for millions of years.

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