Horse
The horse adapted to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families, but only three—Equidae (the horse and related species), Tapiridae (the tapir), and Rhinocerotidae (the rhinoceroses)—have survived to the present day.
Kiang
Molecular phylogenies indicate the most recent common ancestor of all modern equids (members of the genus "Equus") lived ~5.6 (3.9–7.8) mya. Direct paleogenomic sequencing of a 700,000-year-old middle Pleistocene horse metapodial bone from Canada implies a more recent 4.07 Myr before present date for the most recent common ancestor (MRCA) within the range of 4.0 to 4.5 Myr BP. The oldest divergencies are the Asian hemiones (subgenus "E. (Asinus)", including the kulan, onager, and kiang), followed by the African zebras (subgenera "E. (Dolichohippus)", and "E. (Hippotigris)"). All other modern forms including the domesticated horse (and many fossil Pliocene and Pleistocene forms) belong to the subgenus "E. (Equus)" which diverged ~4.8 (3.2–6.5) million years ago.