Why frogs thrived after the dinosaurs were wiped out

Frogs around the world should be grateful for the forces that wiped out dinosaurs 66 million years ago.

That's according to new research from scientists in the United States and China that suggests whatever caused the mass extinction paved the way for the proliferation of frogs.

While frogs have been around for more than 200 million years, new research suggests that three main modern frog lineages — about 88 per cent of the living species of frogs — began to thrive shortly after the extinction event that signalled the end of all non-avian dinosaurs at the end of the Cretaceous Period.

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While we know that about 80 per cent of the world's species were killed off in the mass extinction, what's not known is whether that extended to frogs, as there are few fossilized remains that have been found.

However, the researchers of this new study say that whether or not many frog species became extinct, the event gave rise to the frogs we know today.

"Maybe there was some extinction that happened there," says David Blackburn, co-author of the paper published in the journal Proceedings of the National Academy of Sciences

"At the very least, what happened afterwards was that it seems like there must have been rapid diversification, where we had many new lineages evolve," said Blackburn, who is also associate curator of amphibians and reptiles at the Florida Museum of Natural History.

A changing landscape

Frogs make up about 90 per cent of the world's living amphibian species, and can be found in nearly every corner of the world, with more than 6,700 species.

In order to better understand just how they became one of the most diverse types of vertebrates, the researchers studied 95 genes from 156 previously studied species, together with an additional 145 species.

They found that three main lineages were able to rapidly thrive and diversify shortly after the mass extinction.

At first, when they saw the data come back about the almost simultaneous evolution of three distinct types of frogs — the Hyloidea, Microhylidae and Natatanura — they didn't believe it.

"Nobody had seen this result before," said Peng Zhang, co-author of the study and a professor in the department of biochemistry and molecular biology at Sun Yat-Sen University in China. 

"We redid the analysis using different parameter settings, but the result remained the same. I realized the signal was very strong in our data. What I saw could not be a false thing."

After re-examining their data, they realized that they could trace most of today's frogs to that particular point in time. 

The reason, they surmise, is that while the extinction event was devastating to forests, frogs are incredibly adaptable and able to exist in smaller microhabitats. And once the forests and ecosystems began to thrive again, the frogs were able to thrive along with them.

They were able to live in trees, escaping predators, but were also able to live under the leaves in forests, remaining hidden. They were also able to take advantage of an abundant food source: insects.

"What I think is really exciting about this study is that it sets up new expectations for ... how we might look at the fossil record and what we might hope to find in the fossil record in the future," Blackburn said.