''Astrohippus'' ("Star horse") is an extinct member of the
Equidae
Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. All extant species are in the genus '' Equus'', ...
tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confli ...
Equini, the same tribe that contains the only living equid genus, '' Equus''. Fossil remains have been found in the central
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
,
Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...
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 usu ...
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 the 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 convent ...
of the early
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million 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 million yea ...
s, with the most likely ancestor of ''Astrohippus'' being ''
Pliohippus
''Pliohippus'' (Greek (, "more") and (, "horse")) is an extinction, extinct genus of Equidae, the "horse family". ''Pliohippus'' arose in the middle Miocene, around 15 million years ago. The long and slim limbs of ''Pliohippus'' reveal a quick- ...
Texas
Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
. 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 Pleistoceneabout 13.3—1.8 million years ago (Mya), living around 11.5 million years. This ancient species of three-toed horse grew up to 3 ...
''.http://paleodb.org/cgi-bin/bridge.pl?action=displayCollectionDetails&collection_no=18097&is_real_user=1Coffee Ranch Quarry at the Paleobiology Database 1/2109 '' 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 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