History of the domestic sheep exact line of descent between domestic sheep and their wild ancestors is unclear. The most common hypothesis states that "Ovis aries" is descended from the Asiatic ("O. orientalis") species of mouflon. A few breeds of sheep, such as the Castlemilk Moorit from Scotland, were formed through crossbreeding with wild European mouflon. The urial ("O. vignei") was once thought to have been a forebear of domestic sheep, as they occasionally interbreed with mouflon in the Iranian part of their range. However, the urial, argali ("O. ammon"), and snow sheep ("O. nivicola") have a different number of chromosomes than other Ovis species,
Wild horse taxonomists considered domesticated and wild horse two subspecies of the same species, the valid scientific name was "Equus caballus" Linnaeus 1758, with the subspecies labeled "E. c. caballus" (domesticated horse), "E. c. ferus" Boddaert, 1785 (tarpan) and "E. c. przewalskii" Poliakov, 1881 (Przewalski's horse). However, in 2003, the International Commission on Zoological Nomenclature decided that the scientific names of the wild species have priority over the scientific names of domesticated species, therefore mandating the use of "Equus ferus" for the horse, independent of the position of the domesticated horse. Przewalski's horse occupied the eastern Eurasian Steppes, perhaps from the Urals