Equinae

Mounted skeleton of Pliohippus in the Natural History Museum, Karlsruhe, copyright Ghedoghedo.

Belongs within: Equidae.
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
    |--+--Nannippus Matthew 1926 C96, F99
    |  `--+--Hipparion CR78
    |     `--Neohipparion Gidley 1903 C96, F99
    |          |--N. affine Leidy 1869 F99
    |          `--N. coloradense Osborn 1918 F99
    `--+--Equus CR78
       `--Pliohippus Marsh 1874 C96, C77
            |--P. campestris D07
            |--P. fossulatus D07
            |--P. lullianus D07
            |--P. mexicanus D07
            |--P. mirabilis D07
            |--P. nobilis D07
            |--P. osborni D07
            |--P. pachyops D07
            |--P. pernix D07
            `--P. robustus D07

Equinae incertae sedis:
  Proboscidipparion Sefve 1927 F99
    |--P. houfenense (Teilhard & Young 1931) F99
    |--P. pater Matsumoto 1927 F99
    |--P. rocinantis (Hernandez-Pacheco 1921) F99
    `--P. sinense Sefve 1927 F99
  Pseudhipparion Ameghino 1904 F99
  Dinohippus D07
    |--D. interpolatus D07
    |--D. leardi D07
    |--D. leidyanus D07
    |--D. mexicanus D07
    `--D. spectans D07

*Type species of generic name indicated

REFERENCES

[C96] Campbell, N. A. 1996. Biology 4^th 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.