eohippus
noun
eo·hip·pus ˌē-ō-ˈhi-pəs 
: any of a genus (Hyracotherium synonym Eohippus) of very small primitive horses from the Lower Eocene having 4-toed forefeet and 3-toed hind feet
called also dawn horse
Word History
Etymology
New Latin, from eo- + Greek hippos horse — more at equine
First Known Use
circa 1879, in the meaning defined above