Dinosaur Biodiversity Declined Before Asteroid Chicxulub Impact: Study | Paleontology


The best-known mass extinction was the disappearance of non-avian dinosaurs at the end of the Cretaceous, 66 million years ago, after ruling the Earth for 170 million years. The best-supported extinction model is the impact of a large asteroid in Chicxulub, Mexico. However, it is widely debated whether or not dinosaurs were in decline prior to Chicxulub’s impact. A study in the review Nature Communication provides new evidence of an environmentally-related global decline among dinosaur groups long before the asteroid impact.

Condamine et al. analyze the speciation-extinction dynamics for six key dinosaur families and find a decline among dinosaurs, where diversification shifted to a declining diversity pattern 76 million years ago. Image credit: Jorge Gonzalez.

“We looked at the six most abundant dinosaur families (Ankylosauridae, Ceratopsidae, Hadrosauridae, Dromaeosauridae, Troodontidae and Tyrannosauridae) throughout the Cretaceous period, ranging from 150 to 66 million years ago, and found that they were all evolving and spreading and clearly a success, ”said Dr Fabien Condamine, researcher at the Institute of Evolutionary Sciences in Montpellier and at the CNRS.

“Then, 76 million years ago, they show a sudden slowdown. Their rates of extinction increased, and in some cases the rate of origin of new species dropped.

Dr Condamine and his colleagues used Bayesian modeling techniques to account for several types of uncertainties such as incomplete fossil records, uncertainties in the dating of fossils and uncertainties in evolutionary models.

The models were each run millions of times to examine all of these possible sources of error and to determine whether the analyzes would converge towards an agreed-upon most likely outcome.

“In all cases, we found evidence of the decline before the impact of the bolide,” said Dr Guillaume Guinot, researcher at the Institute of Evolutionary Sciences in Montpellier and at the CNRS.

“We also looked at how these dinosaur ecosystems function, and it became clear that phytophagous species tended to go extinct first, which made the last few dinosaur ecosystems unstable and prone to collapse if environmental conditions turned. damaging. “

“We have used over 1,600 carefully verified records of dinosaurs from across the Cretaceous Period,” added Professor Phil Currie, a paleontologist at the University of Edmonton.

“I have been collecting dinosaurs in North America, Mongolia, China, and other regions for quite some time, and have seen tremendous improvements in our knowledge of the age of rock formations containing dinosaurs.”

“It means the data is improving all the time. The decline of dinosaurs over their last ten million years makes sense, and it is indeed the best-sampled part of their fossil record, as our study shows. “

“In the analyzes, we explored different types of possible causes of the dinosaur decline,” said Professor Mike Benton, a paleontologist at the University of Bristol.

“It became clear that there were two main factors, first that the general climate was getting cooler, which made life more difficult for the dinosaurs who probably depended on the warm temperatures.”

“Second, the loss of herbivores left ecosystems unstable and prone to a cascade of extinction.”

“We also found that longer-lived dinosaur species were more susceptible to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.”

“It was a pivotal moment in the evolution of life,” said Dr. Condamine.

“The world had been dominated by dinosaurs for over 160 million years, and as they declined, other groups began to dominate, including mammals.”

“The dinosaurs were for the most part so huge that they probably barely knew the little furry mammals were out there in the undergrowth.”

“But the mammals started to increase the number of species before the dinosaurs left, and then after the impact, they got a chance to build new types of ecosystems that we see today.”


FL Condamine et al. 2021. Dinosaur biodiversity declined long before the impact of asteroids, influenced by ecological and environmental pressures. Nat Common 12, 3833; doi: 10.1038 / s41467-021-23754-0

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