Climatic changes, understood as environmental factors, have been the main responsible for the great diversification of horses, characterized by a rapid accumulation of species, during the Indian Email Lists last 20 million years. This is the main conclusion of a work led by researchers from the Higher Council for Scientific Research (CSIC) that appears published in the latest issue of the journal Science. Scientists have analyzed 140 species, the vast majority extinct, and have synthesized decades of studies of the fossil record of horses around the planet. The research contradicts the classical theory that explained the multiplication of horse species around 18 million years ago, during the Lower Miocene. This theory suggested that the diversification of the horses would be related to a series of rapid adaptations in response to the expansion of a new environment: the prairies.

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Until now, it was stated that changes in body size and teeth in horses would have played a fundamental role in this great diversification, a scenario that is known in evolution as “adaptive radiation”. “According to classical theory, the horses that populated North America at that time would have changed faster by developing teeth that are more resistant to abrasion, typical of a diet rich in grass. In addition, they would have become bigger and bigger as a requirement to increase the effectiveness of the digestion of this less nutritious food and as a strategy against predators in the new open spaces ”, explains Juan López Cantalapiedra, researcher at the CSIC and the Museum für Naturkunde de Berlin Response to external factors Did size and dentition really evolve so fast during radiation moments of grazing horses? Everything points to no. According to these researchers,

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these morphological changes were slow, because the data collected indicates that the radiation gave rise to species that are very similar in ecology and shape. Therefore, environmental factors, rather than the evolution of these morphological features, influenced the rapid accumulation of species. “Environmental changes have caused the fragmentation of ecosystems on a global scale, which gave rise to isolated populations of horses, genetically different, but with similar morphologies”, points out Manuel Hernández Fernández, a researcher at the Complutense University of Madrid at the Institute of Geosciences. “They also affected productivity, generating ecosystems with enough energy to maintain several very similar species,” adds José Luis Prado, a researcher at the National University of the Center of the Province of Buenos Aires. The climatic changes also facilitated the two great dispersions of the horses from America to Eurasia. These dispersions took place around

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