''Sifrhippus'' is an extinct

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 ...

equid 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 ...

containing the species ''S. sandrae''. ''Sifrhippus'' is the oldest known equid, living during the early

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

. Its fossils were discovered in the

Bighorn Basin The Bighorn Basin is a plateau region and intermontane basin, approximately 100 miles (160 km) wide, in north-central Wyoming in the United States. It is bounded by the Absaroka Range on the west, the Pryor Mountains on the north, the Bigho ...

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

Description

''Sifrhippus'' would have looked quite different to modern horses, being more slender and much smaller, with a relatively small head and longer hindlimbs. Its body was built to leap around the forest undergrowth instead of galloping on open grasslands like later equids. Individuals likely weighed between ; the size variance, according to one theory, depended on the warmth of the climate. Image:Sifrhippus sp..JPG, Life restoration in the Swedish Museum of Natural History Image:Sifrhippus grangeri Wikipedia Juandertal.jpg, Life reconstruction based on living small-bodied, forest-dwelling ungulates.

Taxonomy

''Sifrhippus sandrae'' is referred to in earlier literature as ''Hyracotherium sandrae'', but Froehlich, arguing that the traditional genus ''

Hyracotherium ''Hyracotherium'' ( ; "hyrax-like beast") is an extinction, extinct genus of small (about 60 cm in length) perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal is (for some scientists) considered t ...

'' was not

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, reassigned many of its species to other genera. Froehlich gave ''H. sandrae'' the new generic name ''Sifrhippus'', derived from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

'' صِفْر'' (''ṣifr''), "zero", and

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

ἵππος Hippos () or Sussita (Aramaic, ) is an ancient city and archaeology, archaeological site located on a hill 2 km east of the Sea of Galilee, attached by a topographical saddle to the western slopes of the Golan Heights. Hippos was a Hellenis ...

'' (''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 Perissodactyla Prehistoric placental genera Ypresian life Wasatchian Paleogene mammals of North America Fossil taxa described in 2002