Astrohippus, Calippus, Equus (synonymized with Allozebra, Asinus, Onager, Plesippus, Neohippus, Equus semiplicatus, Equus tau), Hippidion, Onohippidium, Pliohippus, Protohippus (syn. Eoequus)
Astrohippus, Calippus, Dinohippus, Equus (synonymized with Allozebra, Asinus, Onager, Plesippus, Neohippus, Equus semiplicatus, Equus tau), Hippidion, Onohippidium, Pliohippus, Protohippus (synonymized with Eoequus).
The second was a group of smaller horses, known as protohippines, which included Protohippus and Calippus.