''Scaphohippus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of equine, with two known species, known from fossils found in California, New Mexico, Montana, and Nebraska.The Paleobiology Database ''Scaphohippus'' entry
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History

Both species in the genus were originally described as members of the wastebasket taxon '' Merychippus'' in the 1915 by John Merriam. The genus was described from specimens found in the Barstow Formation 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 mi ...

s with hypsodont (high-crowned) teeth.

Phylogenetic relationships

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 The Great Plains is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...

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 International_Code_of_Zoological_Nomenclature, 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 spe ...

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 ...

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 and sometimes abbreviated as S.B. County, is a County (United States), county located in the Southern California, southern portion of the U.S. state of California, and is locat ...

. 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 sep ...

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, Cajon Valley, California and one from the Olcott Formation, Sioux County, Nebraska.The Paleobiology Database East Sand Quarry entry
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''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.

References

{{Taxonbar, from=Q7430156 Miocene horses Miocene Perissodactyla Fossil taxa described in 2006 Miocene mammals of North America Serravallian extinctions Prehistoric placental genera Aquitanian genus first appearances Equinae