Scaphohippus
Encyclopedia
Scaphohippus is an extinct Miocene
genus
of equine
, with two known species, known from fossils found in California, New Mexico, Montana, and Nebraska.
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
s with hypsodont
(high-crowned) teeth.
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.
for the genus, was originally described in 1915 by John Merriam as Merychippus sumani from University of California Museum of Paleontology
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
. 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
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 Foramtion, Sioux County, Nebraska
.
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.
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
genus
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 equine
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...
, with two known species, known from fossils found in California, New Mexico, Montana, and Nebraska.
History
Both species in the genus were originally described as members of the wastebasket taxon MerychippusMerychippus
Merychippus is an extinct proto-horse of the family Equidae that was endemic to North America during the Miocene from 20.43—10.3 Ma living for approximately .It had three toes on each foot and is the first horse known to have grazed...
in the 1915 by John Merriam. The genus was described from specimens found in the Barstow Formation
Barstow Formation
The Barstow Formation is a series of limestones, conglomerates, sandstones, siltstones and shales exposed in the Mojave Desert near Barstow, California. It is early to middle Miocene in age, and lends its name to the Barstovian North American land mammal age...
of southeast California. Specimens of Scaphohippus were medium-sized horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s with hypsodont
Hypsodont
Hypsodont dentition is characterized by high-crowned teeth and enamel which extends past the gum line. This provides extra material for wear and tear. Some examples of animals with hypsodont dentition are cows, horses and deer; all animals that feed on gritty, fibrous material. The opposite...
(high-crowned) teeth.
Phylogenetic relationships
The genus is closely related to ProtohippusProtohippus
Protohippus is an extinct genus of horse....
and Callippus
Callippus
Callippus or Calippus was a Greek astronomer and mathematician.Callippus was born at Cyzicus, and studied under Eudoxus of Cnidus at the Academy of Plato. He also worked with Aristotle at the Lyceum, which means that he was active in Athens prior to Aristotle's death in 322...
. 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
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
late in the Hemingfordian, about 17 to 16 million years ago and invaded the Great Basin
Great Basin
The Great Basin is the largest area of contiguous endorheic watersheds in North America and is noted for its arid conditions and Basin and Range topography that varies from the North American low point at Badwater Basin to the highest point of the contiguous United States, less than away at the...
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.
Scaphohippus sumani
Scaphohippus sumani, the type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
for the genus, was originally described in 1915 by John Merriam as Merychippus sumani from University of California Museum of Paleontology
University of California Museum of Paleontology
The University of California Museum of Paleontology is a paleontology museum located on the campus of the University of California, Berkeley....
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, California
San Bernardino County is a county in the U.S. state of California. As of the 2010 census, the population was 2,035,210, up from 1,709,434 as of the 2000 census...
. 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
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 separate. The palate is divided into two parts, the anterior...
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 Foramtion, Sioux County, Nebraska
Sioux County, Nebraska
-National protected areas:* Agate Fossil Beds National Monument* Nebraska National Forest * Oglala National Grassland -Demographics:...
.
Scaphohippus intermontanus
Scaphohippus intermontanus, the second species in the Scaphohippus genus, is distinguishable from S. sumani by several distinct feature of the teeth. The upper cheek teeth have a height of 40–50 mm at the mesostyle and the protoconeProtocone
thumb|500px|right|Right upper molar showing the four main upper molars cusps.The protocone is a cusp of the molars of the upper dentition in Placental and Marsupial vertebrates .It is found at the mesiolingual area of the tooth...
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.