The shape of the skull and, particularly, the dentition is the result of convergent evolution with the equids, perissodactyl mammals that developed on the northern continents.

The earliest forms of notohippids possessed low-crowned molars, but over the course of evolution, the teeth gradually became more prismatic, and covered with a thick layer of cement.

The first notohippids developed during the Lower Eocene, Pampahippus arising from ancestors likely found in the archaic families Isotemnidae or Oldfieldtomasiidae.

Later, over the course of the Oligocene, more specialized forms emerged, including Notohippus, Rhynchippus Eurygenium, Eomorphippus, Morphippus, Mendozahippus, Pascualihippus, Argyrohippus.

The notohippids are part of the notoungulates, a large group of South American mammals that developed various forms of different appearances andsizes over the course of the Cenozoic.