Przewalski 's horse is one of three known subspecies of Equus ferus , the others being the domesticated horse , Equus ferus caballus and the extinct tarpan ( Equus ferus ferus ) .
Przewalski 's horse is one of three known subspecies of Equus ferus , the others being the domesticated horse , Equus ferus caballus and the extinct tarpan , Equus ferus ferus .