French Press Agency, Posted on Tuesday, June 29, 2021 at 17:13
Long before the asteroid impact ended 65 million years ago, dinosaurs were already in decline, victims of the planet’s cooling climate, according to a study published Tuesday.
The space object’s responsibility for the disappearance has been a consensus in the scientific community, since the discovery of a giant impact crater, in Mexico in 1980.
The collision caused a shockwave that covered Earth with a cloud of dust and gas, disrupting the climate and permanently erasing three-quarters of species, including non-avian dinosaurs, from the map.
But paleontologists are debating whether this mass extinction was sudden, or whether the meteorite just dealt the final blow to an already struggling group.
“This is a debate between antagonists,” biologist Fabian Kondamine, author of the study published in Nature Communications, told AFP.
Because the data are not strong enough to validate one hypothesis over another: “The fossil record (dinosaur bones, editor’s note) is incomplete, in poor conditions of preservation, certain geographic areas such as the tropics are underrepresented, and time periods are not well represented. better information than others. …”, developed CNRS researchers at the Institute of Evolutionary Sciences in Montpellier.
– 1600 fossils –
To correct for this bias, the French-Anglo-Canadian researchers and team used a new statistical modeling method, called Bayesian, which calculates causal probabilities from observations of known elements.
They selected 1,600 fossils belonging to six dinosaur families, including the iconic tyrannosaurs, triceratops and hadrosaurs, of which “Jurassic Park” is best known.
The three families of herbivores, and three of the carnivores, are rich in 247 species. Each fossil is assigned a code that makes it possible to trace successive diagnoses that scientists have made since their discovery.
Thanks to their model, the researchers were able to estimate an age of appearance and extinction for each of the species, over a period ranging from 145 million years, the end of the Cretaceous to 66 million years of Disaster.
The results: “We saw a peak of diversity 76 million years ago, with a high rate of new species formation. Then, a slow decline,” explains Fabian Condamine.
Thus, over a colossal period of 10 million years – longer than the era of the human race – the number of dinosaur species has decreased, from about fifty to less than twenty-66 million years.
Researchers compare these statistics with known and indisputable environmental data (climate, marine, geology, etc.).
– Decreased from 7 to 8 degrees –
The results show a perfect correlation with the climate curve: “The higher the rate of species loss, in the mirror, the lower the temperature,” explains macroevolutionists.
This significant cooling, which caused the Earth to lose 7-8 degrees, began to “build up” at the same time as the dinosaurs retreated.
“Back then, the weather was much warmer, and there were palm trees and mangroves in the Bering Strait” between Siberia and Alaska today, explains Fabian Kondamine.
However, these giants cannot generate their own body heat, as humans do. They depend too much on their environment for food, movement, reproduction… that their metabolism is incapable of adapting to change.
Another key variable: the first disappearances affected herbivores, about two million years before carnivores.
This study suggests that the scarcity of herbivores, prey for carnivores, may have unbalanced ecosystems and led to successive extinctions among other dinosaur families.
In this context, a meteorite with a diameter of 12 km hits Earth. Already weakened, the giant rule was unable to recover from this catastrophe, unlike some small mammals.
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