The modern horse, Equus caballus, concerns to family horse group odd-toeds (Equidae) and forms together with donkeys, asses and zebras genus Equus.
Odd-toeds, including tapirs and rhinoceroses, are descendants of group for a long time dyed out primitive mammal Condylarthra from which there was all hoofed animals. Condylarthra were in size with the fox and are completely not similar on large horses. Their brain very small, and knobby molars testify to the bad adaptation to chafing vegetative food, on what specify and strongly advanced canines. Legs short, five-fingered, terminating in hoofs.
During millions years horse evolution under influence of varying conditions of an inhabitancy occured in a direction of increase in the sizes of animals, reductions of number of fingers and complications of dental system.
Ancestors of a horse at these stages of evolution lived basically on the American continent, but in a consequence there have been superseded by "new" predators and have remained mainly on the Euroasian continent.
The history of a horse totals approximately 60 million years and looks as follows:
55 million years ago Hyracotherium (Eohippus) - "dawn horse"