<P> The famous fossils found near Hagerman , Idaho were originally thought to be a part of the genus Plesippus . Hagerman Fossil Beds ( Idaho ) is a Pliocene site , dating to about 3.5 mya . The fossilized remains were originally called Plesippus shoshonensis , but further study by paleontologists determined the fossils represented the oldest remains of the genus Equus . Their estimated average weight was 425 kg , roughly the size of an Arabian horse . </P>
when did equus first appear in fossil record
about 3.5 mya