Extinction key to vertebrate diversity: Study

Periods of high extinction on Earth, rather than evolutionary adaptations, may have been a key driver in the diversification of today's dominant land vertebrates, including reptiles, birds, and mammals, suggests new research.

Mass extinctions among some groups of amniotes coincide with numerous and large diversifications in other closely related groups, the findings showed.

The research challenges commonly held views that support a relationship between the evolution of "key innovations" in a group and the rapid increase in its number of species.

"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," said study co-author Johannes Muller, professor at Museum fur Naturkunde in Berlin, Germany.

The study examined the issue of adaptive radiations among early amniotes, from 315 to 200 million years ago.

The concept of adaptive radiation is central 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.

Often, if the appearance of an evolutionary novelty coincides temporarily with a large increase in species richness, it is assumed that the innovation is responsible for this pattern.

The scientists used statistical methods to identify which of the amniote groups present during this time were significantly more species-rich than their close relatives, and attempted to identify the factors responsible for this diversity imbalance.

The results showed that usually, large differences in diversity between two closely related groups are not because more species evolve in the larger group, but rather because more species of the smaller group go extinct.

The study was published in the journal Scientific Reports.