Equinae

Merychippus is an extinct proto-horse of the family Equidae that was endemic to North America during the Miocene, 15.97–5.33 million years ago. It had three toes on each foot and is the first horse known to have grazed.

Equinae is a subfamily of the family Equidae, known from the Hemingfordian stage of the Early Miocene (16 million years ago) onwards. They originated in North America, before dispersing to every continent except Australia and Antarctica. They are thought to be a monophyletic grouping. Members of the subfamily are referred to as equines; the only extant equines are the horses, asses, and zebras of the genus Equus, with two other genera Haringtonhippus and Hippidion becoming extinct at the beginning of the Holocene, around 11–12,000 years ago.

Equini is the only living tribe of the subfamily Equinae, which has lived worldwide (except Australia) since the Hemingfordian stage of the Middle Miocene (16–0 mya). It is considered to be a monophyletic clade.

Hipparionini is an extinct tribe of three-toed equids in the subfamily Equinae. They had body forms similar to modern equines, with high-crowned teeth. They first appeared in North America during the Early Miocene around 17 million years ago, before migrating into the Old World around 11.4-11.0 million years ago. The youngest species date to the end of the early Early Pleistocene, becoming extinct following the arrival of modern equines of the genus Equus to the Old World.