WASHINGTON, Dec 8 (Reuters) – The age of the dinosaurs ended in cataclysm on a spring day 66 million years ago when a 12 km wide asteroid hit Mexico’s Yucatan Peninsula, causing the extinction of these remarkable beasts and about three quarters of the Earth. species.
But were the dinosaurs already endangered, with failing diversification and sluggish rates of evolution, as some scientists have proposed? The answer is a resounding “no,” according to a new study that modeled food chains and ecological habitats in North America, the part of the world best represented in the fossil record from that time.
The researchers looked at the 18 million years before the asteroid impact that ended the Cretaceous period and the following 4 million years at the start of the Paleogene period, when mammals asserted their dominance after the dinosaurs died out – outside of their bird lineage.
Based on more than 1,600 fossils, researchers have reconstructed the food chains and habitat preferences of terrestrial and freshwater vertebrates. These included animals like the giant meat-eater T. rex, the three-horned Triceratops, the tank-like Ankylosaurus, crocodiles, turtles, frogs, fish, and various small mammals that lived under the dinosaur feet.
The dinosaurs were entrenched in stable ecological niches for which they were well adapted, the researchers found.
“In other words, the dinosaurs were slaughtered at their peak,” said ecologist Jorge García-Girón of the University of Oulu in Finland and the University of León in Spain, lead author of the research. published in the journal Science Advances.
But the mammals had begun to lay the groundwork for their subsequent rise, diversifying their ecological niches and developing more varied diets, behaviors and climatic tolerances, García-Girón added.
Dinosaurs continued to evolve and adapt during the twilight of their reign, with new species appearing and old ones disappearing, the study found. Some of the main plant eaters like the horned and duck-billed dinosaurs were being replaced by a wider variety of medium-sized herbivores.
Some previous research has suggested that dinosaur biodiversity declined long before the asteroid impact, based on the fossil record of various dinosaur families.
“There was this nagging thought that maybe the dinosaurs were on the verge of extinction anyway, in the midst of a long-term decline, when the asteroid lifted them out of their misery,” the paleontologist said. from the University of Edinburgh and study co-author Steve Brusatte. “We can now say with conviction: the dinosaurs were going strong, with stable ecosystems, until the asteroid suddenly killed them.”
The fact that the dinosaurs were so well adapted to their climate and environment may have been their undoing.
“When the asteroid hit, it threw everything into chaos, and the dinosaurs couldn’t cope with the sudden change in a world they were so used to,” Brusatte said.
“Our study suggests that it is likely the interplay between many other ecological traits, including their body size, diet, behaviors, and ecospace plasticity that primed some smaller animals for greater survival. after the asteroid impact,” said paleontologist and study co-author Alfio Alessandro. Chiarenza from the University of Vigo in Spain.
Mammals around before the asteroid included a now-extinct group of rodents called multituberculates, as well as relatives of today’s marsupials called metatherians and relatives of today’s placentals called eutherians.
After the mass extinction, new mammals appeared, including many true placentals – the group that gives rise to well-developed young, encompassing most of today’s mammals, from whales to bats and aardvarks to humans. Post-apocalyptic mammals rapidly expanded in body size and ecological variety.
“Mammals and dinosaurs have the same origin story – they both originated and began to diversify during the Triassic period, around 230 million years ago, on the supercontinent of Pangea” , Brusatte said.
“From there they split, with the dinosaurs seeking greatness and the mammals relegated to small sizes in the shadows,” Brusatte added. “But their fates would be forever linked. The mammals were there when the asteroid hit. They made it through. We had ancestors staring at the asteroid.”
Reporting by Will Dunham in Washington, editing by Rosalba O’Brien
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