Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...
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 n ...
of equine, with two known species, known from fossils found in California, New Mexico, Montana, and Nebraska.The Paleobiology Database ''Scaphohippus'' entry /ref>
History
Both species in the genus were originally described as members of the
wastebasket taxon
Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically define ...
'' Merychippus'' in the 1915 by John Merriam. The genus was described from specimens found in the
Barstow Formation
The Barstow Formation is a series of limestones, conglomerates, sandstones, siltstones and shales exposed in the Mojave Desert near Barstow in San Bernardino County, California.Dibblee, T.W., Jr. (1967). Areal Geology of the Western Mojave ...
of southeast California. Specimens of ''Scaphohippus'' were medium-sized
horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million ...
The genus is closely related to '' Protohippus'' and '' Callippus''. In the Barstow Formation, the two species of ''Scaphohippus'' occur with only one other hypsodont horse, '' Acritohippus stylodontus''. ''Scaphohippus'' apparently developed on the Great Plains late in the Hemingfordian, about 17 to 16 million years ago and invaded the Great Basin at about 15 million years ago. The Great Plains and Great Basin were then isolated by tectonic barriers and ''Scaphohippus'' became extinct in the Great Plains, but survived in the Great Basin, until the barriers disappeared at about 13 million years ago and ''Scaphohippus'' also became extinct in the Great Basin.
Species
''Scaphohippus sumani''
''Scaphohippus sumani'', the
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 specimen( ...
for the genus, was originally described in 1915 by John Merriam as ''Merychippus sumani'' from
University of California Museum of Paleontology
The University of California Museum of Paleontology (UCMP) is a paleontology museum located on the campus of the University of California, Berkeley.
The museum is within the Valley Life Sciences Building (VLSB), designed by George W. Kelham and ...
specimen number 21422, consisting of four teeth. The specimen was collected from fossiliferous layers of the Barstow Formation outcropping in Rodent Hill Basin,
San Bernardino County, California
San Bernardino County (), officially the County of San Bernardino, is a county located in the southern portion of the U.S. state of California, and is located within the Inland Empire area. As of the 2020 U.S. Census, the population was 2,18 ...
. Specimens of the species have also been found in three other sites in California and one in Nebraska. While numerous specimens of isolated teeth and partial
palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly s ...
s have been found at the type locality, comparatively few complete skulls are known. The few examples from the location are badly crushed or have been altered due to pressure during fossilization. Detailed measurement of teeth from the type locality enabled identification of a ''S. sumani'' skull from the
Punchbowl Formation
The Punchbowl Formation is a sedimentary sandstone geologic formation in the northern San Gabriel Mountains, above the Antelope Valley in Los Angeles County, southern California.Olcott Formation,
Sioux County, Nebraska
Sioux County is a county in the U.S. state of Nebraska. As of the 2010 United States Census, the population was 1,311. Its county seat is Harrison.
Sioux County is included in the Scottsbluff, NE Micropolitan Statistical Area.
In the Nebrask ...
.The Paleobiology Database East Sand Quarry entry /ref>
''Scaphohippus intermontanus''
''Scaphohippus intermontanus'', the second species in the genus ''Scaphohippus'', is distinguishable from ''S. sumani'' by several distinct features of the teeth. The upper cheek teeth have a height of 40–50 mm at the mesostyle and the protocone connects with the protoconule after approximately 30% wear. The enamel fossettes are both simpler and possess fewer plications than those of ''S. sumani''. The species was first described as ''Merychippus intermontanus'' in the same 1915 paper by John Merriam in which ''"Merychippus" sumani'' was described. The type specimen for ''S. intermontanus'' is a section of jaw containing 6 teeth found in the ''Hemicyon'' Tuff, Barstow Formation, that outcrops in Hellgate Basin, San Bernardino County. The species has been confidently identified from several California sites with possible specimens known from Montana and New Mexico.