Dinohippus

Dinohippus (Greek: "Terrible horse") is an extinct equid which was endemic to North America from the late Hemphillian stage of the Miocene through the Zanclean stage of the Pliocene (10.3—3.6 mya) and in existence for approximately . Fossils are widespread throughout North America, being found at more than 30 sites from Florida to Alberta and Panama (Alajuela Formation).
Taxonomy.
Quinn originally referred ""Pliohippus" mexicanus" to "Dinohippus", but unpublished cladistic results in an SVP 2018 conference abstract suggest that "mexicanus" is instead more closely related to extant horses than to "Dinohippus".
Description.
"Dinohippus" was the most common horse in North America and like "Equus", it did not have a dished face. It has a distinctive passive "stay apparatus" formed from bones and tendons to help it conserve energy while standing for long periods. "Dinohippus" was the first horse to show a rudimentary form of this character, providing additional evidence of the close relationship between "Dinohippus" and "Equus". "Dinohippus" was originally thought to be a monodactyl horse, but a 1981 fossil find in Nebraska shows that some were tridactyl. The species "D. leidyanus" had an estimated body mass of approximately .