The age of the dinosaurs came to a tragic end 66 million years ago, when a 12-kilometer-wide asteroid hit Mexico’s Yucatan Peninsula, triggering the extinction of these remarkable beasts and three-quarters of Earth’s species.

But were the dinosaurs already on the verge of extinction, with diversification faltering and a rate of evolution stalling, as some scientists have suggested?

The answer is a definite no, according to a new study that simulated food chains and ecological habitats in North America, the part of the world best represented by archival dinosaur fossils, shows Reuters.

Dinosaurs would have gone extinct right at the peak of their species

The researchers examined the 18 million years before the asteroid impact that ended the Cretaceous and the four million years after, at the beginning of the Paleogene, when mammals took over after the dinosaurs died out – apart from their bird lineage.

The researchers drew on more than 1,600 fossils and reconstructed the food chains and habitat preferences of terrestrial and freshwater vertebrates. Among them were species such as the giant carnivore T. rex, Triceratops with three horns, Ankylosaurustank-like, crocodiles, turtles, fish and various small mammals.

Dinosaurs were rooted in stable ecological niches for which they were adapted, the researchers found.

“In other words, the dinosaurs were brought down right 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 new study.

Dinosaurs may have been extinct even before the asteroid

But mammals had begun to lay the groundwork for their subsequent rise, diversifying their ecological niches and developing more varied diets, behaviors, and climate tolerances.

Dinosaurs continued to evolve and adapt until near the end of their existence. Thus, new species appeared while others disappeared.

Previous studies have suggested that dinosaur biodiversity had already begun to falter long before the asteroid impact, based on fossils from various dinosaur families.

“There was this nagging theory that the dinosaurs would have been on the verge of extinction anyway, in the middle of a long-term decline, when the asteroid wiped it off the face of the planet. Now we can say with conviction that the dinosaurs were doing well, having stable ecosystems, even until the asteroid suddenly killed them,” said Steve Brusatte, paleontologist and co-author of the study.

How did small animals survive such a large asteroid?

The fact that the dinosaurs were so well adapted to their climate and environment may have even caused their extinction.

“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 was probably the interplay of many other ecological features, including body size, diets, behaviors and exospatial plasticity, that primed certain smaller animals for greater survival after the asteroid impact,” said the paleontologist and study co-author Alfio Alessandro Chiarenza of the University of Vigo, Spain.

“We had ancestors who looked at the asteroid”

After the mass extinction, new mammals emerged, including many true placentals—the group that gives birth to well-developed young that includes most mammals today, from whales to bats and aardvarks to humans. “Post-apocalyptic” mammals expanded rapidly in body size and ecological variety.

“Mammals and dinosaurs share the same origin story – both arose and began to diversify during the Triassic period, about 230 million years ago, on the supercontinent Pangea. But their destinies would be forever intertwined. The mammals were there when the asteroid hit. They managed to survive. We had ancestors who looked at the asteroid,” said Brusatte.

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