Eohippus (now known as Hyracotherium) is a relative to modern horses, but whether a direct ancestor, or a distant cousin remains unclear.

There were, in fact, a number of related hyracothere species in existence at that time (just as now there are a number of different of horse species, which include zebras).

Hyracotheria lived in the early Eocene, a period marked by global warming (the so-called Palaeocene-Eocene thermal maximum - reference).