Miohippus
Encyclopedia
Miohippus was a genus
of prehistoric horse existing longer than most Equidae
. Miohippus lived in what is now North America
during the Oligocene approximately 32-25 million years ago. While descending genera of this species lived during the Miocene period, the 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 Oligocene.
Miochippus species are commonly referred to as the three-toed horses. Their range was from Alberta, Canada to Florida
to California
.
in 1874 and its type is Miohippus annectens. It was assigned to Equidae
by Marsh in 1874. It was synonymized subjectively with Mesohippus
by Matthew
in 1899. It was assigned again by Hay
(1902), H. F. Osborn
in 1918, Hay (1930), Stirton (1940) and Carroll (1988); and to Anchitheriinae by MacFadden in 1998.
The species M. obliquidens dating from 34.9 to 30.0 Ma found in Montana
, North Dakota
, South Dakota
, and Nebraska
when calculated for estimated body mass were within the margin of 25 to 30 kg.
Mesohippus became much larger than Miohippus. They weighed around 40 to 55 kilograms. They were somewhat larger than most earlier Eocene
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 was subtly different. Miohippus also had a variable extra crest on its upper molar
s, 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
s, while the other remained suited to life on prairie
s. The forest form led to the birth of Kalobatippus (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
via the Bering Strait
land bridge, and from there moved into Europe
, where its fossil
s were formerly described under the name Anchitherium. Kalobatippus is then believed to have evolved into a form known as Hyohippus, which became extinct near the beginning of the Pliocene
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of prehistoric horse existing longer than most Equidae
Equidae
Equidae is the taxonomic family of horses and related animals, including the extant horses, donkeys, 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
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
during the Oligocene approximately 32-25 million years ago. While descending genera of this species lived during the Miocene period, the 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 Oligocene.
Miochippus species are commonly referred to as the three-toed horses. Their range was from Alberta, Canada to Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Taxonomy
Miohippus was named by MarshOthniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
in 1874 and its type is Miohippus annectens. It was assigned to Equidae
Equidae
Equidae is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus...
by Marsh in 1874. It was synonymized subjectively with Mesohippus
Mesohippus
Mesohippus is an extinct genus of early horse. It lived some 40 to 30 million years ago from the late Eocene to the mid-Oligocene...
by Matthew
William Diller Matthew
William Diller Matthew FRS was a vertebrate paleontologist who worked primarily on mammal fossils....
in 1899. It was assigned again by Hay
Oliver Perry Hay
Oliver Perry Hay was an American professor, herpetologist, ichthyologist, and paleontologist. From 1894-1895 he worked at the Field Museum of Natural History as Assistant Curator of Zoology where, despite his specialty in ichthyology, he worked in all non-ornithological fields of zoology...
(1902), H. F. Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
in 1918, Hay (1930), Stirton (1940) and Carroll (1988); and to Anchitheriinae by MacFadden in 1998.
Species
- M. anceps
- M. annectens syn. with M. crassicuspis
- M. assiniboiensis
- M. condon
- M. equiceps syn. with Anchitherium brachylophus
- M. gemmarosae
- M. gidleyi (syn. with Mesohippus grallipes, Mesohippus validus)
- M. grandis
- M. intermedius
- M. longicristis
- M. obliquidens syn. with Mesohippus barbour, Mesohippus brachystylus, Mesohippus eulophus, M. meteulophus, Pediohippus antiquus
- M. primus
- M. quartus
Morphology
Three specimens were examined for estimated body mass by M. Mendoza, C. M. Janis, and P. Palmqvist. These specimens were estimated to weigh:The species M. obliquidens dating from 34.9 to 30.0 Ma found in Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
, South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, and Nebraska
Nebraska
Nebraska is a state on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha, on the Missouri River....
when calculated for estimated body mass were within the margin of 25 to 30 kg.
Mesohippus became much larger than Miohippus. They weighed around 40 to 55 kilograms. They were somewhat larger than most earlier Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
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
Fossa (anatomy)
In anatomical terminology, fossa has come to mean a depression or hollow, in general, in a bone. Other parts of the body may be involved, for example, the antecubital fossa...
was deeper and more expanded, and the ankle joint was subtly different. Miohippus also had a variable extra crest on its upper molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s, 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
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
s, while the other remained suited to life on prairie
Prairie
Prairies are considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type...
s. The forest form led to the birth of Kalobatippus (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
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
via the Bering Strait
Bering Strait
The Bering Strait , known to natives as Imakpik, is a sea strait between Cape Dezhnev, Chukotka Autonomous Okrug, Russia, the easternmost point of the Asian continent and Cape Prince of Wales, Alaska, USA, the westernmost point of the North American continent, with latitude of about 65°40'N,...
land bridge, and from there moved into Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, where its fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s were formerly described under the name Anchitherium. Kalobatippus is then believed to have evolved into a form known as Hyohippus, which became extinct near the beginning of the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
.