Eohippus angustidens (originally Eohippus validus Cope 1875, Marsh 1876; 30cm at shoulder; Early Eocene, 55mya) along with Mesohippus was derived from a sister to Hyracotherium and gave rise to horses and indricotheres. The canines are large. The engraving makes the premolars look like molars, but the skull does not indicate such a change. The postfrontal is rectangular. The prefrontal is large. The manus has four fingers. The pes has three toes that touch the ground.

Mesohippus bairdi (Marsh 1875; 1m in length; Middle Eocene) was derived from a sister toHyracotherium and gave rise to horses and indricotheres. Mesohippus had longer, more slender legs and smaller canines. The skull remained as longer as the neck. Several species are known.