Dinosaurs May Have Been Declining Before the Asteroid Struck Earth

The researchers say the cataclysmic impact may have simply been the final nail in the dinos’ coffin

An illustration depicting some of the dinosaurs that roamed the Earth during the Late Cretaceous. Jorge Gonzalez

Non-avian dinosaurs were already in decline some 10 million years before the asteroid impact that ended their reign over the planet 66 million years ago, according to a new study published this week in the journal Nature Communications.

“The alternative scenario is that dinosaur diversity was not that high and was instead lower just before the asteroid impact than millions of years before,” Fabien Condamine, a paleontologist at the Institute of Evolutionary Science of Montpellier in France and the study’s lead author, tells Krista Charles of New Scientist. “Here, the meteorite is seen as a coup de grâce for dinosaurs, which would have been declining.”

Condamine and his co-authors plugged the data from a trove of 1,600 dinosaur fossils from 247 species into a computer model to determine which way the arc of dinosaur diversification was bending toward the end of their time on Earth. The analysis revealed that in the Late Cretaceous, though dinosaurs still dominated most ecosystems, dinosaur extinction rates increased and relatively few new species appeared to replenish their declining diversity, reports George Dvorsky for Gizmodo.

"Many paleontologists think dinosaurs would have continued to live if the asteroid did not hit Earth. Our study brings new information for this question, and it seems that dinosaurs were not in good shape before the impact," Condamine tells Aylin Woodward of Business Insider.

Per Insider, the researchers say this waning diversity among the dinosaurs that did not evolve into birds coincided with a period of global cooling that started around 76 million years ago—and the changing climate may have been a contributing factor, especially among plant eating dinosaurs.

“It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures,” Mike Benton, co-author of the study and paleontologist at the University of Bristol’s School of Earth Sciences, says in a statement. “Then, the loss of herbivores made the ecosystems unstable and prone to [an] extinction cascade. We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.”

But not everyone is convinced.

“This kind of information cannot really be shown with these sort of methods because ultimately it is the underlying data that really matter. And the fossil record is really incomplete,” Alfio Alessandro Chiarenza, a paleontologist at the University of Vigo in Spain who wasn’t involved in the study, tells New Scientist.

In particular, Chiarenza highlighted the fact that roughly 60 percent of North America isn’t represented in the fossil record for the Late Cretaceous because only certain locations preserved fossils from that era.

“We don’t know what’s going on in Africa, we don’t know the diversity in most of Europe,” Chiarenza tells New Scientist. “In Asia, we don’t have the right rocks that precede the extinction.”