Belongs within: Equoidea.
Contains: Anchitheriinae.
The Equidae, horses and their fossil relatives, are a group of perissodactyls known from the early Eocene to the present. Most members of the family are distinctly cursorial though the earliest examples were less so.
<==Equidae |--Minippus Froehlich 2002F02 | |--*M. index (Cope 1873) [=Hyracotherium index]F02 | `--M. jicarillai Froehlich 2002F02 `--Arenahippus Froehlich 2002F02 |--*A. grangeri (Kitts 1956) [=Hyracotherium angustidens grangeri]F02 `--+--A. aemulor (Gingerich 1991) [=Hyracotherium aemulor]F02 `--+--A. pernix (Marsh 1876) [=Hyracotherium pernix, Eohippus pernix; incl. H. seekinsi Morris 1968]F02 `--+--Xenicohippus Bown & Kihm 1981F02 | |--X. craspedotum (Cope 1880) [=Hyracotherium craspedotum, Eohippus craspedotus]F02 | `--+--*X. grangeri Bown & Kihm 1981F02 | `--X. osborni Bown & Kihm 1981F02 `--+--Eohippus Marsh 1876F02 | `--E. angustidens (Cope 1875)F02 (see below for synonymy) `--+--Pliolophus vulpiceps Owen 1858 [=Hyracotherium vulpiceps]F02 `--Protorohippus Wortman 1896F02 |--P. montanum Wortman 1896F02 `--+--*P. venticolum (Cope 1881) [=Eohippus venticolum, Hyracotherium vasacciense venticolum]F02 `--+--+--Haplohippus McGrew 1953S99, M76 | | `--H. texanus McGrew 1953H96 | `--Orohippus Marsh 1874F02, C77 | |--O. agilis Marsh 1873H96, C77 [=Hyracotherium agileC77] | |--O. major Marsh 1874H96 | |--O. pumilus Marsh 1872C77 | `--O. sylvaticusSP96 `--+--Epihippus Marsh 1878F02, D07 | |--E. gracilis (Marsh 1871) (see below for synonymy)H96 | |--E. (Duchesnehippus) intermediusP96 | `--E. parvus Granger 1908RH14, H96 `--+--+--AnchitheriinaeC96 | `--MiohippusC96 | |--M. assiniboiensis (Lambe 1905)S96 | |--M. equiceps (Cope 1879)S96 | |--M. gemmarosae Osborn 1918S96 | |--M. gidleyiWT08 | |--M. grandis (Clark & Beerbower 1967)S96 | |--M. intermedius (Osborn & Wortman 1895)S96 | `--M. obliquidensTPG96 `--Mesohippus Marsh 1876M76, D07 |--M. bairdi (Leidy 1850)S96 |--M. eulophusD07 |--M. gridleiD07 |--M. intermediusD07 |--M. obliquidensD07 |--M. portentusTPG96 |--M. propinquus Lambe 1905S96 |--M. texanus McGrew 1971H96 |--M. validusD07 `--M. westoni (Cope 1889)S96 Equidae incertae sedis: HippotheriumC77 |--H. affineC77 |--H. calamarium Cope 1875C77 |--H. gratumC77 |--H. occidentaleC77 |--H. panienseC77 `--H. speciosumC77 PlesiohipparionTH03 Eoequus wilsoni Quinn 1955F99 Propachynolophus Lemoine 1891RH14, SM93 `--P. gaudryiRH14 Eurohippus parvumRH14
Eohippus angustidens (Cope 1875)F02 [=Orohippus angustidensF02, Hyracotherium angustidensF02; incl. *E. validus Marsh 1876F02, Orohippus cuspidatus Cope 1875C77, Hyracotherium cuspidatumF02, H. loevii Cope 1877F02, Orohippus vasacciensis Cope 1875C77, H. vasaccienseF02, Lophiotherium vasaccienseC77]
Epihippus gracilis (Marsh 1871) [=Anchitherium gracilis; incl. Orohippus uintensis Marsh 1875, Epihippus uintensis]H96
*Type species of generic name indicated
References
[C96] Campbell, N. A. 1996. Biology 4th ed. The Benjamin/Cummings Publishing Company, Inc.: Menlo Park (California).
[C77] Cope, E. D. 1877. Report upon the extinct Vertebrata obtained in New Mexico by parties of the expedition of 1874. Geographical Surveys West of the One Hundredth Meridian 4 (2): i–iv, 1–370.
[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.
[F99] Forsten, A. 1999. Snout proportions in some Eurasian hipparions (Mammalia, Equidae): taxonomic and functional implications. Geodiversitas 21 (2): 255–278.
[F02] Froehlich, D. J. 2002. Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zoological Journal of the Linnean Society 134: 141–256.
[H96] Hanson, C. B. 1996. Stratigraphy and vertebrate faunas of the Bridgerian-Duchesnean Clarno Formation, north-central Oregon. In: Prothero, D. R., & R. J. Emry (eds) The Terrestrial Eocene–Oligocene Transition in North America pp. 206–239. Cambridge University Press.
[M76] MacFadden, B. J. 1976. Cladistic analysis of primitive equids, with notes on other perissodactyls. Systematic Zoology 25 (1): 1–14.
[P96] Prothero, D. R. 1996. Magnetic stratigraphy and biostratigraphy of the Middle Eocene Uinta Formation, Uinta Basin, Utah. In: Prothero, D. R., & R. J. Emry (eds) The Terrestrial Eocene–Oligocene Transition in North America pp. 3–24. Cambridge University Press.
[RH14] Rose, K. D., L. T. Holbrook, R. S. Rana, K. Kumar, K. E. Jones, H. E. Ahrens, P. Missiaen, A. Sahni & T. Smith. 2014. Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications 5: 5570.
[S99] Stanley, S. M. 1999. Earth System History. W. H. Freeman and Company: New York.
[S96] Storer, J. E. 1996. Eocene-Oligocene faunas of the Cypress Hills Formation, Saskatchewan. In: Prothero, D. R., & R. J. Emry (eds) The Terrestrial Eocene–Oligocene Transition in North America pp. 240–261. Cambridge University Press.
[SM93] Stucky, R. K., & M. C. McKenna. 1993. Mammalia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 739–771. Chapman & Hall: London.
[SP96] Stucky, R. K., D. R. Prothero, W. G. Lohr & J. R. Snyder. 1996. Magnetic stratigraphy, sedimentology, and mammalian faunas of the Early Uintan Washakie Formation, Sand Wash Bain, northwestern Colorado. In: Prothero, D. R., & R. J. Emry (eds) The Terrestrial Eocene–Oligocene Transition in North America pp. 40–51. Cambridge University Press.
[TPG96] Tabrum, A. R., D. R. Prothero & D. Garcia. 1996. Magnetostratigraphy and biostratigraphy of the Eocene-Oligocene transition, southwestern Montana. In: Prothero, D. R., & R. J. Emry (eds) The Terrestrial Eocene–Oligocene Transition in North America pp. 278–311. Cambridge University Press.
[TH03] Tedford, R. H., & C. R. Harington. 2003. An Arctic mammal fauna from the Early Pliocene of North America. Nature 425: 388–390.
[WT08] Wang, X., & R. H. Tedford. 2008. Dogs: Their fossil relatives and evolutionary history. Columbia University Press: New York.