Why have horses changed over time?

A fresh look at the evolution of the horse

Changes in the environment and in ecosystems have been the driving force behind the evolution of horses over the past 20 million years. This is the conclusion reached by a new study by a team of paleontologists from Spain and Argentina, including Juan L. Cantalapietra, Humboldt Fellow at the Museum für Naturkunde Berlin, which is now being carried out in Science is published. The research team examined 140 species of horses, most of which are extinct. It summed up decades of research into the fossil fuel evolution of this popular group of mammals.

Their conclusions challenge a classic theory that links the evolutionary success of horses to various new adaptations to life in open grasslands 18 million years ago. “According to this theory, horses should have developed faster in the steppe environment. They developed more resilient teeth that did not wear out as quickly with the predominant consumption of grass. They also got bigger in order to better utilize this nutritionally poor feed. In addition, the size offered protection from predators in this new, open habitat, ”explains Juan L. Cantalapiedra, researcher at the Museum für Naturkunde in Berlin.

Previously, it was assumed that teeth and body size developed in a short time. According to recent results, these evolutionary changes may have taken more time than previously thought. Cantalapiedra and his colleagues were even able to show that all newly developed horse species were ecologically very similar. It therefore looks as if the evolutionary changes cannot be explained by a new diversity of ecological roles, but rather by an increasing diversity of the environment.

“Changes in the environment could have created a mosaic of fragmented ecosystems in which different horse populations with similar needs and adaptations to the environment could develop in isolation from one another. Different species with a similar appearance could have developed, ”explains Manuel Hernández Fernández from the Universidad Complutense in Madrid. "That was probably only possible in ecosystems in which there was a lot of energy and biomass available, so that species that were very similar and otherwise would have competed strongly with one another could all survive," adds Jose Luis Prado of the Universidad del Centro de la Provincia de Buenos Aires added.

The diversification of horse species accelerated twice more when the changed sea level eleven million years ago and then again four million years ago enabled horses to migrate from North America to Eurasia and Africa. At that time, new species actually appeared very quickly, but did not show any dramatic changes on the outside.

Original publication:

J.L. Cantalapiedra, J.L. Prado, M. Hernández Fernández, M. T. Alberdi. Decoupled ecomorphological evolution and diversification in Neogene-Quaternary horses. Science.