Belongs within: Anchitheriinae.
Contains: Hipparion, Equus.
The Equinae are a group of horses in which the lateral toes are reduced and non-functional, or lost entirely (Churcher & Richardson 1978).
Characters (from Churcher & Richardson 1978): Skull with postorbital bar. Upper incisors with more or less developed infundibula; in later forms on some or all lower incisors also. Cheek teeth hypsodont, crown height equal to or greater than mesiodistal diameter; cementum in fossettes and in later forms over all of crown; small enamel folds or plis present on lophs, often numerous. Premolars 2 to 4 fully molarised; P1s small or absent. Upper molars with protolophs and metalophs joining ectolophs even in early stages of wear; premolars with transverse lophs potentially remaining free until late stage of wear; fossettes usually closing with wear. Protocone separate or nearly detached from protoloph; elongate, with major diameter oriented mesiodistally. Lower molars with pattern composed of two crescentic lophids joined in middle of tooth; metaconid and metastylid completely fused, mesiodistally elongated, forming double loop in later forms. Ulna greatly reduced in shaft, sometimes incomplete, usually fused to radius. Metapodial III and phalanges relatively elongated; lateral metapodials and digits narrowed, moved posteriorly to limb axis; distal ends of metapodials bent posteriorly. Lateral hoofed phalanges laterally compressed, not extending to plantar surface of III; in latest forms lateral phalanges lost, lateral metapodials reduced to splint bones.
Equinae
| i. s.: Proboscidipparion Sefve 1927F99
| |--P. houfenense (Teilhard & Young 1931)F99
| |--P. pater Matsumoto 1927F99
| |--P. rocinantis (Hernandez-Pacheco 1921)F99
| `--P. sinense Sefve 1927F99
| AstrohippusS99
| ParahipparionS99
|--+--+--Pseudhipparion Ameghino 1904S99, F99
| | | `--P. retrusumWT08
| | `--+--HipparionCR78
| | `--Neohipparion Gidley 1903C96, F99
| | |--N. affine Leidy 1869F99
| | |--N. coloradense Osborn 1918F99
| | `--N. leptodeWT08
| `--+--CormohipparionS99
| | |--C. goorisi MacFadden & Skinner 1981F99
| | |--C. occidentale Leidy 1856F99
| | `--C. sphenodus Cope 1885F99
| `--Nannippus Matthew 1926C96, F99
| |--N. westoniS99
| `--+--N. lenticularisS99
| `--+--N. aztecusS99
| `--+--N. breckensisS99
| `--N. peninsulatusS99
`--+--+--CalippusS99
| `--Protohippus Leidy 1869S99, C77
| `--P. sejunctusC77
`--+--+--EquusCR78
| `--DinohippusS99
| |--D. interpolatusD07
| |--D. leardiD07
| |--D. leidyanusD07
| |--D. mexicanusD07
| `--D. spectansD07
`--Pliohippus Marsh 1874C96, C77
|--P. campestrisD07
|--P. fossulatusD07
|--P. lullianusD07
|--P. mexicanusD07
|--P. mirabilisD07
|--P. nobilisD07
|--P. osborniD07
|--P. pachyopsD07
|--P. pernixD07
`--P. robustusD07*Type species of generic name indicated
References
[C96] Campbell, N. A. 1996. Biology 4th ed. The Benjamin/Cummings Publishing Company, Inc.: Menlo Park (California).
[CR78] Churcher, C. S., & M. L. Richardson. 1978. Equidae. In: Maglio, V. J., & H. B. S. Cooke (eds) Evolution of African Mammals pp. 379–422. Harvard University Press: Cambridge (Massachusetts).
[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.
[S99] Stanley, S. M. 1999. Earth System History. W. H. Freeman and Company: New York.
[WT08] Wang, X., & R. H. Tedford. 2008. Dogs: Their fossil relatives and evolutionary history. Columbia University Press: New York.