A new study provides the strongest evidence yet that the dinosaurs were struck down in their prime and were not in decline, at the time the asteroid hit.

Landmark study reveals that dinosaurs dominated the world right up until a deadly asteroid hit Earth, leading to their mass extinction, around 66 million years ago.

The findings, which were published in the journal Science Advances on December 7, provide the strongest evidence yet that dinosaurs were struck down in their prime. At the time the Chicxulub asteroid hit, dinosaurs were not in decline.

Scientists have long debated why non-bird dinosaurs, including Tyrannosaurus rex and Triceratops, became extinct – whereas mammals and other species such as turtles and crocodiles survived.

Led by an international team of paleontologists and ecologists, the study analyzed 1,600 fossil records from North America. Researchers modeled the food chains and ecological habitats of land-living and freshwater animals during the last several million years of the Cretaceous, and the first few million years of the Paleogene period, after the asteroid hit.

For some time paleontologists have known that many small mammals lived alongside the dinosaurs. However, this research reveals that these mammals were diversifying their diets, adapting to their environments, and becoming more important components of ecosystems as the Cretaceous unfolded. Meanwhile, the dinosaurs were entrenched in stable niches to which they were supremely well adapted.

Mammals didn’t just take advantage of the dinosaurs dying, experts say. They were creating their own advantages through diversifying – by occupying new ecological niches, evolving more varied diets and behaviors, and enduring small shifts in climate, by rapidly adapting. These behaviors probably helped them to survive, as they were better able than the dinosaurs to cope with the radical and abrupt destruction caused by the asteroid.