''Sifrhippus'' is an extinct
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
equid
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'', w ...
containing the species ''S. sandrae''. ''Sifrhippus'' is the oldest known equid, living during the early
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
. Its fossils were discovered in the
Bighorn Basin of
Wyoming
Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
.
Description
![Sifrhippus sp](https://upload.wikimedia.org/wikipedia/commons/f/fe/Sifrhippus_sp..JPG)
''Sifrhippus'' looked similar to modern horses, but were more slender and much smaller. Individuals likely weighed between ; the size variance, according to one theory, depended on the warmth of the climate.
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Taxonomy
''Sifrhippus sandrae'' is referred to in earlier literature as ''Hyracotherium sandrae'', but Froehlich, arguing that the traditional genus '' Hyracotherium'' was not monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
, reassigned many of its species to other genera. Froehlich gave ''H. sandrae'' the new generic
Generic or generics may refer to:
In business
* Generic term, a common name used for a range or class of similar things not protected by trademark
* Generic brand, a brand for a product that does not have an associated brand or trademark, other ...
name ''Sifrhippus'', derived from the Arabic
Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...
'' صِفْر'' (''ṣifr''), "zero", and Greek '' ἵππος'' (''híppos''), "horse".
Since Froehlich's reorganization of ''Hyracotherium'' based on the morphological differences between fossil specimens, one further study has suggested that ''Sifrhippus sandrae'' and ''Minippus jicarillai'' are synonymous, and also that ''Minippus index'', although not seen by the authors of this study, is a synonym for the same taxon, which should then be named ''Sifrhippus index''. It has been argued that the differences in the fossils are more likely caused by individual variation in animals.
References
{{Taxonbar, from=Q291458
Eocene horses
Eocene odd-toed ungulates
Prehistoric placental genera
Ypresian life
Wasatchian
Paleogene mammals of North America
Fossil taxa described in 2002