Wild horses seem to be the current “invasive species de jour,” with antagonists claiming they do not belong. However, horses of many different subspecies, including the modern horse, were native to North America long before Europeans arrived.
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Fossils from the Equidae family of horses and burros have been found from as early as the Paleocene epoch (66 to 56 million years ago). Although these initial horses were much smaller than the modern-day horses we know, they rapidly evolved into larger species during the Miocene epoch (23.8 to 5.3 million years ago). Paleontologists have excavated fossil remains of horses across North America with such abundance they were 60 percent of the biomass collected.
The current horse genus, Equus, was in place four million years ago. The oldest oldest-known species of the genus Equus in North America is Equus simplicidens, also known as the Hagerman horse, Hagerman zebra, and American zebra. Its appearance was relatively similar to the modern horse. These early species of Equus were so successful that they expanded their range outside the continent. They first migrated to South America and later spread into Asia, Europe, and Africa.
However, there was a period in time when horses vanished from the continent, and the reason remains unknown. About 10,000 years ago, most of North America’s large mammals, including Equus species, went extinct at the end of the Pleistocene. The cause of their extinction is widely debated among the scientific community, with no definitive conclusion.
When humans first explored North America, horses made up 25 percent of the biomass of all living creatures
