Wild Horse - Evolution and Taxonomy

Evolution and Taxonomy

The horse family Equidae and the genus Equus evolved in North America, before the species moved into the Eastern Hemisphere. Studies using ancient DNA as well as DNA of recent individuals, shows the presence of two closely related horse species in North America, the Wild Horse and the "New World stilt-legged horse;" the latter is taxonomically assigned to various names. Currently, three subspecies that lived during recorded human history are recognized. One subspecies is the widespread domestic horse (Equus ferus caballus), as well as two wild subspecies, the recently-extinct Tarpan (Equus ferus ferus) and the endangered Przewalski's Horse (Equus ferus przewalskii). Genetically, the pre-domestication horse, Equus ferus ferus, and domesticated horse, Equus ferus caballus, form a single homogeneous group (clade) and are genetically indistinguishable from each other. The genetic variation within this clade shows only a limited regional variation, with a notable exception of Przewalski's Horse. Przewalski's Horse has several unique genetic differences that distinguishes it from the other subspecies, including 66 instead of 64 chromosomes, unique Y-chromosome gene haplotypes, and unique mtDNA haplotypes. Besides genetic differences, osteological evidence from across the Eurasian wild horse range, based on cranial and metacarpal differences, indicates the presence of only two subspecies in post-glacial times, the Tarpan and Przewalski's Horse.