Equidae
Equidae (commonly known as the horse family) is the Taxonomy (biology), taxonomic Family (biology), family of Wild horse, horses and related animals, including Asinus, asses, zebra, zebras, and many extinct species known only from fossils. The fa ...
tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...
Equini, the same tribe that contains the only living equid genus, '' Equus''. Fossil remains have been found in the
central United States
The Central United States is sometimes conceived as between the Eastern United States, Eastern and Western United States, Western as part of a three-region model, roughly coincident with the United States Census Bureau, U.S. Census Bureau's d ...
,
Florida
Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
Jalisco
Jalisco, officially the Free and Sovereign State of Jalisco, is one of the 31 states which, along with Mexico City, comprise the 32 Political divisions of Mexico, Federal Entities of Mexico. It is located in western Mexico and is bordered by s ...
, and
Guanajuato
Guanajuato, officially the Free and Sovereign State of Guanajuato, is one of the 32 states that make up the Political divisions of Mexico, Federal Entities of Mexico. It is divided into Municipalities of Guanajuato, 46 municipalities and its cap ...
. The fossils date in time from the oldest dating from the
Barstovian
The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 16,300,000 to 13,600,000 years BP, a period of . It is usua ...
in the
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 ...
to the youngest dating in the
Hemphillian
The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered t ...
faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by conven ...
of the early
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58
Based on study of the tooth morphology it is considered unlikely that ''Astrohippus'' could be an ancestor of modern
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 the most likely ancestor of ''Astrohippus'' being '' Pliohippus''.MacFadden, B. J. (1984). "Astrohippus and Dinohippus". ''J. Vert. Paleon''. 4(2):273–283.
The species '' Astrohippus ansae'' was originally described by W. D. Matthew and R. A. Stirton based on several cheek teeth found in the Coffee Ranch quarry,
Hemphill County
Hemphill County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 3,382. The county seat and only incorporated community in the county is the city of Canadian. The county was created in 1876 and or ...
,
Texas
Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
. This quarry has produced the remains of six other equid genera including ''
Dinohippus
''Dinohippus'' ( Greek: "Terrible horse") is an extinct equid which was endemic to North America from the late Hemphillian stage of the Miocene through the Zanclean stage of the Pliocene (10.3—3.6 mya) and in existence for approximately . Foss ...
'' and ''
Nannippus
''Nannippus'' is an extinct genus of three-toed horse endemic to North America during the Miocene through Pleistocene, about 13.3—1.8 million years ago (Mya), living around 11.5 million years. This ancient species of three-toed horse grew up to ...
''.Paleobiology Database Ranch Quarry at the Paleobiology Database 1/210 /ref> '' Astrohippus stockii'' was described from the Yepomera locality in Chihuahua, Mexico, by J.F. Lance in 1950 as ''Pliohippus stockii''. The species was moved to ''Astrohippus'' five years later by Quinn. The species ''Astrohippus albidens'' was named by O. Mooser in 1965 from Mexico, the taxon was reassigned to the genus ''
Dinohippus
''Dinohippus'' ( Greek: "Terrible horse") is an extinct equid which was endemic to North America from the late Hemphillian stage of the Miocene through the Zanclean stage of the Pliocene (10.3—3.6 mya) and in existence for approximately . Foss ...
'' in 1988 by T. S. Kelly and E. B. Lander. In 1998 ''A. stockii'' and ''A. albidens'' were combined by T. S. Kelly, with the older ''A. stockii'' name being retained and ''A. albidens'' becoming a junior synonym.
Both species of ''Astrohippus'' have been reported to occur in the
Ocote Local Fauna
Ocote is a common name for various species of pine trees in the genus ''Pinus'' that occur in the Spanish speaking Americas—Latin America.
They include:
*''Pinus apulcensis''
*''Pinus ayacahuite''
*'' Pinus cooperi''
*''Pinus devoniana''
*''Pi ...
of Guanajuato, Mexico by O. Mooser in 1973. 1973 "Pliocene Horses of the Ocote Local Fauna, Central Plateau of Mexico Pliocene Horses of the Ocote Local Fauna, Central Plateau of Mexico" ''The Southwestern Naturalist'' 18(3):257–268