Equidae is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. The family evolved around 50 million years ago from a small, multi-toed ungulate into larger, single-toed animals. All extant species are in the genus Equus, which originated in North America. Equidae belongs to the order Perissodactyla, which includes the extant tapirs and rhinoceros, and several extinct families.
Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla, are animals—ungulates—that have reduced the weight-bearing toes to three or one of the five original toes. The nonweight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, the even-toed ungulates bear most of their weight equally on four or two of the five toes: their third and fourth toes. Another difference between the two is that odd-toed ungulates digest plant cellulose in their intestines, rather than in one or more stomach chambers as even-toed ungulates, with the exception of Suina, do.
Hyracotherium is an extinct genus of very small perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal is considered to be the earliest known member of Equidae before the type species, H. leporinum, was reclassified as a palaeothere, a perissodactyl family basal to both horses and brontotheres. The remaining species are now thought to belong to different genera, such as Eohippus, which had previously been synonymised with Hyracotherium.
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.
Equus is a genus of mammals in the family Equidae, which includes horses, asses, and zebras. Within the Equidae, Equus is the only recognized extant genus, comprising seven living species. Like Equidae more broadly, Equus has numerous extinct species known only from fossils. The genus most likely originated in North America and spread quickly to the Old World. Equines are odd-toed ungulates with slender legs, long heads, relatively long necks, manes, and long tails. All species are herbivorous, and mostly grazers, with simpler digestive systems than ruminants but able to subsist on lower-quality vegetation.
Hagerman Fossil Beds National Monument near Hagerman, Idaho, contains the largest concentration of Hagerman horse fossils in North America. The fossil horses for which the monument is famous have been found in only one locale in the northern portion of the monument called the Hagerman Horse Quarry. The 4,351-acre (17.61 km2) monument is internationally significant because it protects the world's richest known fossil deposits from the late Pliocene epoch, 3.5 million years ago. These plants and animals represent the last glimpse of that time that existed before the Ice Age, and the earliest appearances of modern flora and fauna. This is also significant because the fossils present during this period of the Pliocene represent species which were alive during the early stages in the evolution of humans, albeit on a different continent. The fossil beds were designated a National Natural Landmark in 1975 and was reclassified as a National Monument in 1988.
The wild horse is a species of the genus Equus, which includes as subspecies the modern domesticated horse as well as the endangered Przewalski's horse. The European wild horse, also known as the tarpan, that went extinct in the late 19th or early 20th century has previously been treated as the nominate subspecies of wild horse, Equus ferus ferus, but more recent studies have cast doubt on whether tarpans were truly wild or if they actually were feral horses or hybrids.
Equus lambei, commonly known as the Yukon horse or Yukon wild horse, is an extinct species of the genus Equus. Equus lambei ranged across North America until approximately 10,000 years ago. Based on recent examinations of the mtDNA of Equus lambei remains, scientists have concluded that E. lambei was probably much like the extinct tarpan, also known as the Eurasian wild horse, and the living Przewalski's horse. A partial carcass of Equus lambei is on display at the Yukon Beringia Interpretive Centre in Whitehorse, Yukon.
Stegomastodon is an extinct genus of gomphotheres, a family of proboscideans. It ranged throughout North America from the early Blancan ~4 Ma, to the early Irvingtonian. The South American species have been synonymized with Notiomastodon platensis.
Hippidion is an extinct genus of equine that lived in South America from the Late Pliocene to the end of the Late Pleistocene (Lujanian), between 2.5 million and 11,000 years ago. They were one of two lineages of equines native to South America during the Pleistocene epoch, alongside Equus (Amerhippus) neogeus.
The evolution of the horse, a mammal of the family Equidae, occurred over a geologic time scale of 50 million years, transforming the small, dog-sized, forest-dwelling Eohippus into the modern horse. Paleozoologists have been able to piece together a more complete outline of the evolutionary lineage of the modern horse than of any other animal. Much of this evolution took place in North America, where horses originated but became extinct about 10,000 years ago, before being reintroduced in the 15th century.
Equus simplicidens, sometimes known as the Hagerman horse or the American Zebra is an extinct species of equine native to North America during the Pliocene. It is one of the oldest and most primitive members of the genus Equus. Abundant remains of it were discovered in 1928 in Hagerman, Idaho. It is the state fossil of Idaho.
Carpocyon is an extinct genus of the Borophaginae subfamily of canids native to North America. It lived from the Middle to the Late Miocene, 13.6 to 5.3 Ma Mya, existing for approximately 16.5 million years. The four species in the genus varied in size, with the largest being about the size of a wolf; all had relatively small teeth, suggesting a diet that was more omnivorous than that of other contemporary borophagines.
The latter half of the Late Pleistocene to the beginning of the Holocene saw extinctions of numerous predominantly megafaunal species, which resulted in a collapse in faunal density and diversity across the globe. The extinctions during the Late Pleistocene are differentiated from previous extinctions by the widespread absence of ecological succession to replace these extinct megafaunal species, and the regime shift of previously established faunal relationships and habitats as a consequence. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors. Human impact on megafauna populations is thought to have been driven by hunting ("overkill") as well as possibly environmental alteration. The relative importance of human vs climatic factors in the extinctions has been the subject of long-running controversy.
Haringtonhippus is an extinct genus of equine from the Pleistocene of North America The genus is monospecific, consisting of the species H. francisci, initially described in 1915 by Oliver Perry Hay as Equus francisci. Prior to the naming of the genus, it was sometimes referred to as the New World stilt-legged horse, in reference to its slender distal limb bones, in contrast with those of contemporary "stout legged" caballine true horses.
Equus conversidens, or the Mexican horse, is a dubious Pleistocene species of horse, now extinct, that inhabited North America.
Equus semplicatus was a Pleistocene species of New World stilt-legged horse, and considered the type species for the stilt legged horses, one of three lineages of equids within the Americas, the other two being hippidionid and caballine horses. Now extinct, Equus semiplicatus once inhabited North America.
Equus neogeus is an extinct species of equine native to South America during the Pleistocene. It was formerly thought to be several distinct species within the subgenus Amerhippus, but was later shown to be a single morphologically variable species. It is thought to be closely related to true horses.
Horses have been an important component of American life and culture since before the founding of the nation. In 2008, there were an estimated 9.2 million horses in the United States, with 4.6 million citizens involved in businesses related to horses. There are an estimated 82,000 feral horses that roam freely in the wild in certain parts of the country, mostly in the Western United States.
Equus niobrarensis is an extinct species of Equus, the genus that includes the horse. E. niobrarensis may be synonymous with Equus scotti. It was "stout-legged" and belonged to the "big horses" category as defined by M. C. Winans. The skull of the horse was noted as being broader than Equus caballus.
