Dinosaurs may have already been going extinct before the asteroid hit

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dinosaurs

Even before an enormous asteroid struck Earth, dinosaurs may have been losing species diversity

Jorge Gonzalez

There is new evidence that the diversity of non-avian dinosaur species may have been declining 10 million years before they vanished when a large asteroid hit Earth 66 million years ago.

Palaeontologists have been debating whether this was the case for decades. Many believe that the diversity of  non-avian dinosaur species was still high prior to their extinction. Some researchers even suspect that the dinosaurs were still diversifying at the time.

“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,” says Fabien Condamine at the Institute of Evolutionary Science of Montpellier in France. “Here, the meteorite is seen as a coup de grâce for dinosaurs, which would have been declining.”

Condamine and his colleagues analysed data related to 1600 dinosaur fossils and used the information to model diversity trends.

They found a pattern of declining dinosaur diversity toward the end of the Cretaceous period, supporting the idea that dinosaurs were more diverse several million years before their extinction than they were just prior to the extinction event.

The team also suggests that global cooling at the end of the Cretaceous and a decline of herbivorous dinosaurs – which would have been the cornerstone holding these ecosystems together – would have eventually led to a cascade effect triggering extinctions even if the asteroid hadn’t struck.

However, on the other side of the debate, Alfio Alessandro Chiarenza at the University of Vigo in Spain still isn’t convinced. He and others believe that the extinctions were sudden and wouldn’t have happened without the asteroid impact.

“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,” says Chiarenza. He points out that we don’t have fossils from 60 per cent of North America, because late Cretaceous rocks aren’t preserved in many places. “We don’t know what’s going on in Africa, we don’t know the diversity in most of Europe. In Asia, we don’t have the right rocks that precede the extinction.”

Journal reference: Nature Communications, DOI: 10.1038/s41467-021-23754-0

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