Horses and donkeys, domesticated about 5000 BCE, are feral in open grasslands worldwide ("see" feral horse). In Portugal, feral horses are called Sorraia; in Australia, they are called Brumbies; in the American west, they are called Mustangs. Other isolated feral populations exist, including the Chincoteague Pony and the Banker Horse. They are often referred to as "wild horses," but this is not correct. There are truly "wild" horses that have never been tamed, most notably Przewalski's Horse. While the horse was originally indigenous to North America, the wild ancestor died out at the end of the last Ice Age. In both Australia and the Americas, modern "wild" horses have come from domesticated horses brought by European explorers and settlers that escaped, spread, and thrived.