Only two never-domesticated "wild" groups survived into historic times, Przewalski's horse ("Equus ferus przewalski"), and the Tarpan ("Equus ferus ferus"). The Tarpan became extinct in the late 19th century and Przewalski's horse is endangered; it became extinct in the wild during the 1960s, but was re-introduced in the late 1980s to two preserves in Mongolia. Although researchers such as Marija Gimbutas theorized that the horses of the Chalcolithic period were Przewalski's, more recent genetic studies indicate that Przewalski's horse is not an ancestor to modern domesticated horses. Other now-extinct subspecies of "Equus ferus" appears to have been the stock from which domesticated horses are descended.