Around 36 million years ago, soon after the development of "Mesohippus", "Miohippus" ("lesser horse") emerged, the earliest species being "Miohippus assiniboiensis". As with "Mesohippus", the appearance of "Miohippus" was relatively abrupt, though a few transitional fossils linking the two genera have been found. "Mesohippus" was once believed to have anagenetically evolved into "Miohippus" by a gradual series of progressions, but new evidence has shown its evolution was cladogenetic: a "Miohippus" population split off from the main genus "Mesohippus", coexisted with "Mesohippus" for around four million years, and then over time came to replace "Mesohippus".