Environmental factors driving the rapid expansion of species over the past 20 million years

Changing environments and ecosystems have driven the evolution of horses over the past 20 million years. This is the main conclusion of a new study published in Science by a team of Spanish and Argentinian paleontologists. The team analyzed 140 horse species, most of them extinct, synthesizing decades of research into the fossil history of this popular group of mammals.

Their findings challenge a classic theory, which links the evolutionary success of horses to several new adaptations in response to the spread of grasslands around 18 million years ago. “According to the classic view, horses would have evolved more rapidly when the grasslands appeared, developing teeth that were more resistant to the stronger wear that accompanies a grass-dominated diet. They also grew larger to digest this more efficiently. poor quality food, and as a strategy against predators in these new open habitats,” says Juan L. Cantalapiedra, a researcher at the Museum für Naturkunde in Berlin, Germany.

But have teeth and body size really evolved so quickly? It seems not. According to the new findings, these evolutionary changes could have been much slower than previously assumed. In fact, Cantalapiedra and his colleagues were able to show that all of these newly evolved horse species were ecologically very similar. Thus, rather than a multiplication of ecological roles, the new findings point to external factors, such as increasing environmental heterogeneity, as the main evolutionary force.

“Environmental changes would have produced much more fragmented, mosaic-like ecosystems, where populations of horses with similar requirements and adaptations could have evolved in isolation from each other, resulting in different species but with a similar appearance,” points out Manuel Hernández Fernández at the Complutense University of Madrid. “This was probably only possible in ecosystems rich in energy and biomass, so that very similar species, which otherwise would have been in strong competition, were all able to survive,” adds Jose Luis Prado, from the University. National Center. of the Province of Buenos Aires.

Diversification was further accelerated twice, “when changes in sea level allowed their migration from North America to Eurasia and Africa, 11 and 4 million years ago”, explains María Teresa Alberdi, from the National Museum of Natural Sciences in Madrid. “Then, again, new species appeared very quickly, but without showing dramatic changes in appearance,” Cantalapiedra concludes.

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Material provided by Spanish National Research Council (CSIC). Note: Content may be edited for style and length.

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