The dinosaurs were probably not in decline before the impact of the asteroid that, possibly associated with intense volcanic activity, killed them 66 million years ago.
Previously, the researchers used the fossil record and some mathematical predictions to suggest that dinosaurs could already have been in decline, with the amount and diversity of species that fall before the impact of the asteroid.
Now, in a new analysis that models the changing environment and distribution of dinosaur species in North America, researchers at Imperial College London, University College London and the University of Bristol have shown that dinosaurs were probably not declining before the meteorite.
Alessandro Chiarenza, a student at the Department of Earth Sciences and Engineering in Imperial, said in a statement: "Dinosaurs were probably not condemned to extinction until the end of the Cretaceous, when the asteroid struck, declaring the end of his reign and leaving the planet to animals such as mammals and lizards, and a smaller group of surviving dinosaurs: the birds.
"The results of our study suggest that the dinosaurs as a whole were adaptable animals, able to cope with environmental changes and climatic fluctuations that occurred during the last million years of the Upper Cretaceous. Climate change on long time scales did not cause much long-term decline of the dinosaurs in the later stages of this period. "
The study, published in Nature Communications, shows how the changing conditions of fossilization make previous analyzes have underestimated the number of species at the end of the Cretaceous.
The team focused its study on North America, where many Late Cretaceous dinosaurs are conserved, as Tyrannosaurus rex and Triceratops. During this period, the continent was divided in two by a large inland sea.
In the western half there was a constant supply of sediment from the Rocky Mountains, which were forming, and created the perfect conditions for dinosaurs to fossilize once they died. The eastern half of the continent was characterized by much less suitable conditions for fossilization.
Dinosaurs roamed throughout North America
This means that many more fossils of dinosaurs are found in the western half, and it is this fossil record that is often used to suggest that dinosaurs were in decline during the few million years before the asteroid attack.
Philip Mannion, of University College London, commented: "Most of what we know about the North American dinosaurs of the Late Cretaceous comes from an area smaller than a third of the current continent, and yet we know that the dinosaurs roamed throughout North America, from Alaska to New Jersey and to Mexico. "
Instead of using this uniquely known record, the team used the "ecological niche model." This approach models the environmental conditions, such as temperature and rainfall, that each species needs to survive.
The team then mapped where these conditions would occur across the continent and over time. This allowed them to create an image of where the groups of dinosaur species could survive as conditions changed, rather than simply where their fossils had been found.
The team discovered that habitats that could support a variety of dinosaur groups actually they were more widespread at the end of the Cretaceous, but they were in areas less likely to preserve fossils.
In addition, these areas potentially rich in dinosaurs were smaller wherever they occurred, reducing again the probability of finding a fossil in each of these areas.