Dinosaurs were in their prime until an asteroid hit the Earth 66 million years ago

A study suggests that dinosaurs ruled the planet until a devastating asteroid strike caused their global extinction 66 million years ago.

Led by the University of Edinburgh, the University of Oulu, and the University of León researchers, the study shows the most compelling proof that dinosaurs were wiped off in their prime. As per the University of Edinburgh, dinosaurs were not extinct when the Chicxulub asteroid struck the Earth.

Scientists have long discussed why mammals and other animals, such as turtles and crocodiles, survived while non-bird dinosaurs, such as Tyrannosaurus rex and Triceratops, perished.

The researchers examined 1,600 fossil records from North America in search of novel explanations. After the asteroid collision, during the last few million years of the Cretaceous period and the first few million years of the Paleogene, researchers modeled the food chains and biological environments of animals that lived on land and in freshwater.

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

"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."

Important components of ecosystems

Long known to paleontologists, numerous small mammals coexisted with dinosaurs. But as the Cretaceous period progressed, the research showed that these mammals were changing their diets, adjusting to their habitats, and playing a bigger role in ecosystems.

The dinosaurs, on the other hand, were firmly established in ecological niches to which they were remarkably well adapted. According to researchers, mammals didn't only benefit from the demise of dinosaurs. By diversifying, they were developing benefits for themselves. They did this by occupying new ecological niches, changing their diets and behaviors, and quickly responding to minuscule climatic changes.

"Dinosaurs were going strong, with stable ecosystems"

Experts believe these behaviors helped them survive the asteroid attack because they were more adapted than dinosaurs to deal with sudden and violent damage.

"Dinosaurs were going strong, with stable ecosystems, right until the asteroid suddenly killed them off. Meanwhile, mammals were diversifying their diets, ecologies, and behaviors while dinosaurs were still alive," said Prof. Steve Brusatte, senior author and Personal Chair of Paleontology and Evolution, School of GeoSciences, University of Edinburgh.

"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."

The study was published in Science Advances on December 7.

Study abstract:

It has long been debated why groups such as non-avian dinosaurs became extinct, whereas mammals and other lineages survived the Cretaceous/Paleogene mass extinction 66 million years ago. We used Markov networks, ecological niche partitioning, and Earth System models to reconstruct North American food webs and simulate ecospace occupancy before and after the extinction event. We find a shift in the latest Cretaceous dinosaur faunas, as medium-sized species counterbalanced a loss of megaherbivores. Still, dinosaur niches were otherwise stable and static, potentially contributing to their demise. Smaller vertebrates, including mammals, followed a consistent trajectory of increasing trophic impact and relaxation of niche limits beginning in the latest Cretaceous and continuing after the mass extinction. Mammals did not simply proliferate after the extinction event; rather, their earlier ecological diversification might have helped them survive.