Pliohippus, Meryhippus and Mesohippus were intermediates in this evolution.
The horse evolved from the tiny Eohippus 65 million years ago. Its evolution is known from the fossil record.
The Facts Are .....
The fossils said to form the ancestral tree of the modern horse have been put in order of ascending height, the number of their toes, and their assumed evolutionary age. These specimens have a few problems which negate their inclusion in the sequence:- the number of ribs varies within the series, from 15, to 19, and then down to 18; and the number of lumbar vertebrae changes from 6, to 8, and back to 6. Creation Ex Nihilo, Vol. 14, No. 1, 1992 p:50
As an example of the fact that evolution is not scientifically proven, there are not one, but twenty different genealogical trees of the so-called horse fossil series. Scott M. Huse, "The Collapse of Evolution", Baker Book House: Grand Rapids (Michigan), 1983 p:106
Fossils of three-toed and one-toed animals, which are said to be evolutionary ancestors of the modern horse, have been found preserved in the same rock formation (Nebraska, USA). This proves that they lived together at the same time, and it is obvious that one could not have evolved into the other. Evolution demands that there has to be many millions of years between the three-toed and the one-toed species in the 60-65 million year evolution of the horse. National Geographic, January 1981 p:74
Two modern-day horses, Equus nevadenis & Equus occidentalis, have both been found in the same fossil strata as the so-called “Dawn Horse”, Eohippus. This fact is fatal to the notion of the evolution of the horse, as both horses are equally as old as Eohippus, and therefore could not have evolved from it. Scott M. Huse, "The Collapse of Evolution", Baker Book House: Grand Rapids (Michigan), 1983 p:106
"The supposed pedigree of the Equidae [ie horses, asses, zebras etc] is a deceitful delusion, which
..... in no way enlightens us on the palaeontological origin of the horse". Written by French palaeontologist and evolutionist Charles Deperet in "Transformations of the Animal World", Arno Press: New York, 1980 p:105
"Classic cases of Darwinian change in the fossil record, such as the evolution of the horse in North America have had to be discarded or modified as a result of more detailed information". Written by palaeontologist and evolutionist Dr David Raup (Curator of the Field Museum of Natural History, Chicago) in his article "Conflicts Between Darwin and Paleontology", in The Field Museum of Natural History Bulletin, Vol. 50, No. 1, January 1979 p:25
"The uniform, continuous transformation of Hyracotherium into Equus, so dear to the hearts of generations of textbook writers, never happened in nature ....." Written by ardent evolutionist George Gaylord Simpson in his book "Life of the Past", Yale University Press: New Haven (Connecticut), 1953 p:125
"I admit that an awful lot of that has gotten into the textbooks as though it were true. For instance, the most famous example still on exhibit downstairs [in the American Museum] is the exhibit on horse evolution prepared perhaps 50 years ago. That has been presented as literal truth in textbook after textbook. Now I think that that is lamentable, particularly because the people who propose these kinds of stories themselves may be aware of the speculative nature of some of the stuff. But by the time it filters down to the textbooks, we've got science as truth and we've got a problem". The view of horse evolution expressed by Dr Niles Eldredge, curator at the American Museum of Natural History. Recorded in an interview with Luther Sunderland, and written in his book "Darwin's Enigma: Fossils and Other Problems", Master Books:California 1988 p:78
David Raup of the Field Museum of Natural History urges all to "..abandon belief in the evolution of the horse". Field Museum of Natural History Bulletin, Vol. 5, No. 1, 1979