Archaeohippus is an extinct genus of horse that existed during the Miocene epoch, approximately 23-5.3 million years ago. Other synonyms for Archaeohippus include "Hypohippus", "Anchitherium", and "Megahippus". These names were assigned to various species of the horse genus based on their physical characteristics. For example, "Hypohippus" means "little horse" and was named because of the animal's relatively small size. "Anchitherium" was named after its resemblance to a donkey, while "Megahippus" means "large horse" and was named based on its size. All of these synonyms refer to different species of horses within the Archaeohippus genus, which were crucial to the evolution of modern-day equines.