Extinction is Key for High Species Diversity Today

In order to get terrestrial diversity, you may need extinction. Scientists have found that periods of high extinction on Earth have been the drivers of the diversification of amniotes, which include today's land vertebrates, such as reptiles, birds, and mammals.

In this latest study, the researchers examined the issue of adaptive radiations among early amniotes, from 315 to 200 million years ago. This time period witnessed some of the most profound climate changes on a global scale, including the dramatic shrinking of the southern polar icecap, the disappearance of equatorial rainforests, a substantial increase in temperature, and prolonged drought conditions. The time period under study also included the largest mass extinction in Earth's early history about 252 million years ago.

The idea of adaptive radiation is key to modern evolutionary biology. An adaptive radiation is an extremely rapid increase in the number of species in a group, often as a result of a key evolutionary innovation, which gives the group an advantage over its competitors or allows it to exploit a new resource.

What's interesting is that researchers found that even an appearance of an important innovation in the larger group does not trigger a large proliferation of species until a major next extinction takes place.

"We really did not expect any of these patterns," said Johannes Muller, co-author of the new study, in a news release. "Our results go against many of the traditional predictions from evolutionary biology, and show that the scientific views about the relevance of key innovations should be carefully reconsidered."

The findings are published in the journal Scientific Reports.

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