''Miohippus'' (meaning "small horse") was a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of prehistoric horse existing longer than most

Equidae Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. All extant species are in the genus '' Equus'', ...

. ''Miohippus'' lived in what is now North America from 32 to 25 million years ago, during the late

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

to late Oligocene. ''Miohippus'' was a horse of the Oligocene. According to the Florida Museum of Natural History, Othniel Charles Marsh first believed ''Miohippus'' lived during the Miocene and thus named the genus using this incorrect conclusion. More recent research provides evidence that ''Miohippus'' actually lived during the Paleogene period. ''Miohippus'' species are commonly referred to as the three-toed horses. Their range was from

Alberta, Canada Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Territ ...

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

Taxonomy

The type species of ''Miohippus'', ''M. annectens'', was named by

Marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...

in 1874. It is classified as a member of the subfamily Anchitheriinae following MacFadden (1998).B. J. MacFadden. 1998. Equidae. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America 1:537-559.Paleobiology Database ''Miohippus'' entry
Accessed 8 December 2011

Species list

:* ''M. anceps'' Marsh, 1874 :* ''M. annectens'' Marsh, 1874

Type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

:* ''M. assiniboiensis'' Lambe, 1905 :* ''M. condoni'' Leidy, 1870 :* ''M. equiceps'' Cope, 1879 :* ''M. equinanus'' Osborn, 1918 :* ''M. gemmarosae'' Osborn, 1918 :* ''M. gidleyi'' Osborn, 1904 :* ''M. intermedius'' Osborn & Wortman, 1895 :* ''M. longicristis'' Cope, 1878 :* ''M. obliquidens'' Osborn, 1904 :* ''M. primus'' Osborn, 1918 :* ''M. quartus'' Osborn, 1918

Description

The species ''M. obliquidens'' dating from 34.9 to 30.0 Ma found in

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, So ...

South Dakota South Dakota (; Sioux: , ) is a U.S. state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota and Dakota Sioux Native American tribes, who comprise a large porti ...

, and

Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...

when calculated for estimated body mass were within the margin of 25 to 30 kg. ''Miohippus'' became much larger than ''Mesohippus''. They weighed around 40 to 55 kilograms. They were somewhat larger than most earlier

horse ancestors, but still much smaller than modern horses, which typically weigh about 500 kilograms. ''Miohippus'' was larger than ''Mesohippus'' and had a slightly longer skull. Its facial fossa was deeper and more expanded, and the

ankle joint The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...

was subtly different. ''Miohippus'' also had a variable extra crest on its upper molars, which gave it a larger surface area for chewing tougher forage. This would become a typical characteristic of the teeth of later equine species. ''Miohippus'' had two forms, one of which adjusted to the life in

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

s, while the other remained suited to life on

prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...

s. The forest form led to the birth of ''

Kalobatippus ''Kalobatippus'' ('stilt walking horse') was a genus of Anchitheriinae The Anchitheriinae are an extinct subfamily of the Perissodactyla family Equidae, the same family which includes modern horses, zebras and donkeys. This subfamily is more ...

'' (or ''Miohippus intermedius''), whose second and fourth finger again elongated for travel on the softer primeval forest grounds. The ''Kalobatippus'' managed to relocate to

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

via the Bering Strait land bridge, and from there moved into

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

, where its

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s were formerly described under the name ''Anchitherium''. ''Kalobatippus'' is then believed to have evolved into a form known as ''

Hypohippus ''Hypohippus'' (Greek: "under" (hypos), "horse" (hippos)) is an extinct genus of three-toed horse, which lived 17–11 million years ago. It was the largest anchitherine equid about the size of a modern domestic horse, at and long. It was a lo ...

'', which became extinct near the beginning of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 As many as eight species of ''Miohippus'' were described from the John Day Formation of Oregon, but recent work on the dental variation has determined that only one species of ''Miohippus'' was present within a given member.

References

Evolution of the Horse

by Kathleen Hunt

{{Taxonbar, from=Q942905 Fossils of Canada Paleontology in Alberta Eocene horses Oligocene horses Eocene mammals of North America Oligocene mammals of North America Prehistoric placental genera Prehistoric mammals of North America Eocene genus first appearances Oligocene extinctions Fossil taxa described in 1874 Taxa named by Othniel Charles Marsh

Taxonomy

Species list

Description

See also

References