The Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the latest Aquitanian and Burdigalian of the Early Miocene. The Hemingfordian is preceded by the Arikareean and followed by the Barstovian NALMA stages.
The Hemingfordian can be further divided into the substages of:
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.
The subfamily contains two tribes, the Equini and the Hipparionini, as well as two unplaced genera, Merychippus and Scaphohippus. Members of the family ancestrally had three toes, while members of the tribe Equini from the Middle Miocene onwards developed monodactyl feet.
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.
The Harrisonian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 24,800,000 to 20,600,000 years BP, a period of 4.2 million years. It is usually considered to overlap the Chattian and Aquitanian stages within the late Paleogene. The Harrisonian is preceded by the Monroecreekian and followed by the Hemingfordian NALMA stage.