University of Edinburgh (UK) Dinosaurs were on the up before asteroid downfall

Dinosaurs dominated the world right up until a deadly asteroid hit the earth, leading to their mass extinction, some 66 million years ago, a study reveals.

Fresh insights into the habitats and food types that supported the dinosaurs suggest that their environments were robust and thriving, until the fateful day, at the end of the Cretaceous period.

Strong evidence

The findings provide the strongest evidence yet that the dinosaurs were struck down in their prime and were not in decline, at the time the asteroid hit.

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.

The study, led by an international team of paleontologists and ecologists, analysed 1,600 fossil records from North America to find fresh answers.

Researchers modelled the food chains and ecological habitats of animals that lived on land and in freshwater during the last several million years of the Cretaceous and the first few million years of the Paleogene period, which followed the asteroid strike.

Diversification

Paleontologists have long known that many small mammals lived alongside the dinosaurs. But 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 ecological niches to which they were supremely well adapted.

Mammals did not 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 behaviours and and rapidly adapting to endure small shifts in climate.

Survival

Experts say these behaviours probably helped them to survive the asteroid strike, as they were better suited than the dinosaurs to cope with the radical and abrupt destruction.

“Dinosaurs were going strong, with stable ecosystems, right until the asteroid suddenly killed them off. Meanwhile, mammals were diversifying their diets, ecologies and behaviours while dinosaurs were still alive. So it wasn’t simply that mammals took advantage of the dinosaurs dying, but they were making their own advantages, which ecologically preadapted them to survive the extinction and move into niches left vacant by the dead dinosaurs.”

—Professor Steve Brusatte,Senior author and Personal Chair of Paleontology and Evolution, School of GeoSciences, University of Edinburgh.

“Our study provides a compelling picture of the ecological structure, food webs, and niches of the last dinosaur-dominated ecosystems of the Cretaceous period and the first mammal-dominated ecosystems after the asteroid hit. This helps us to understand one of the age-old mysteries of paleontology: why all the non-bird dinosaurs died, but birds and mammals endured.”

—Jorge García-Girón,First author, Geography Research Unit, University of Oulu, Finland and Department of Biodiversity and Environmental Management, University of León, Spain.

“It seems that the stable ecology of the last dinosaurs actually hindered their survival in the wake of the asteroid impact, which abruptly changed the ecological rules of the time. Conversely, some birds, mammals, crocodilians, and turtles had previously been better adapted to unstable and rapid shifts in their environments, which might have made them better able to survive when things suddenly went bad when the asteroid hit.”

—Alfio Alessandro Chiarenza,Co-lead author, Department of Ecology and Animal Biology, University of Vigo, Spain.

The research is published in the journal Science Advances. It was funded by National Science Foundation (USA), Academy of Finland, European Union Next Generation European Research Council (ERC) Starting Grant, European Union’s Horizon 2020 Research and Innovation Programme, Juan de la Cierva Formación 2020 Fellowship funded by the Ministry of Science and Innovation from the European Union Next Generation.