fact
Small Eocene Horses
The first equid was Hyracotherium, a small forest animal of the early Eocene. This little animal (10-20" at the shoulder) looked nothing at all like a horse. It had a "doggish" look with an arched back, short neck, short snout, short legs, and long tail. It browsed on fruit and fairly soft foliage, and probably scampered from thicket to thicket like a modern muntjac deer, only stupider, slower, and not as agile. This famous little equid was once known by the lovely name "Eohippus", meaning "dawn horse". Some Hyracotherium traits to notice:
Legs were flexible and rotatable with all major bones present and unfused.
4 toes on each front foot, 3 on hind feet. Vestiges of 1st (& 2nd, behind) toes still present. Hyracotherium walked on pads; its feet were like a dog's padded feet, except with small "hoofies" on each toe instead of claws.
Small brain with especially small frontal lobes.
Low-crowned teeth with 3 incisors, 1 canine, 4 distinct premolars and 3 "grinding" molars in each side of each jaw (this is the "primitive mammalian formula" of teeth). The cusps of the molars were slightly connected in low crests. Typical teeth of an omnivorous browser.
At this point in the early Eocene, equids were not yet very different from the other perissodactyl groups; the Hyracotherium genus includes some species closely related to (or even ancestral to) rhinos and tapirs, as well as species that are distinctly equine. [Note: the particular species that probably gave rise to the rest of the equids, H. vassacciense, may be renamed, perhaps to "Protorohippus".]
Though in retrospect we may consider Hyracotherium to be "primitive", it was a very successful animal in its time, and seems to have found a nice stable niche for itself. In fact,
throughout most of the Eocene (a good long 20 million years), only minor evolutionary changes took place in Hyracotherium and its near descendants. The body and feet stayed mostly the same, with slight changes in the toes. The major change was in the teeth; as Eocene equids started to eat more plant browse and less fruit, they developed more grinding teeth to deal with the slightly tougher food
Fact or CRaP
Today's horses evolved from a dog like ancestor, the Hyracotherium.