Equidae

Mounted skeleton of Merychippus in the Nebraska State Museum of Natural History, copyright James St. John.

Belongs within: Equoidea.
Contains: Equinae, 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 2002 F02
    |    |--*M. index (Cope 1873) [=Hyracotherium index] F02
    |    `--M. jicarillai Froehlich 2002 F02
    `--Arenahippus Froehlich 2002 F02
         |--*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 1981 F02
                  |    |--X. craspedotum (Cope 1880) [=Hyracotherium craspedotum, Eohippus craspedotus] F02
                  |    `--+--*X. grangeri Bown & Kihm 1981 F02
                  |       `--X. osborni Bown & Kihm 1981 F02
                  `--+--Eohippus Marsh 1876 F02
                     |    `--E. angustidens (Cope 1875) F02 (see below for synonymy)
                     `--+--Pliolophus vulpiceps Owen 1858 [=Hyracotherium vulpiceps] F02
                        `--Protorohippus Wortman 1896 F02
                             |--P. montanum Wortman 1896 F02
                             `--+--*P. venticolum (Cope 1881) (see below for synonymy) F02
                                `--+--Haplohippus McGrew 1953 M76
                                   |--Orohippus Marsh 1874 F02, C77
                                   |    |--O. major F02
                                   |    `--O. pumilus Marsh 1872 C77
                                   `--+--Epihippus Marsh 1878 F02, D07
                                      |    |--E. gracilis D07
                                      |    |--E. parvus RH14
                                      |    `--E. uintensis D07
                                      `--+--Mesohippus Marsh 1876 M76, D07
                                         |    |--M. bairdi OB13
                                         |    |--M. eulophus D07
                                         |    |--M. gridlei D07
                                         |    |--M. intermedius D07
                                         |    |--M. obliquidens D07
                                         |    `--M. validus D07
                                         `--+--Miohippus grandis C96, OB13
                                            `--+--+--Parahippus Leidy 1858 C96, D07
                                               |  |    |--P. leonensis D07
                                               |  |    |--P. mourningi D07
                                               |  |    |--P. pawniensis D07
                                               |  |    `--P. pristinus D07
                                               |  `--+--+--Callipus C96
                                               |     |  `--Equinae M76
                                               |     `--Merychippus Leidy 1857 C96, D07
                                               |          |--M. brevidontus Bode 1934 B76
                                               |          |--M. californicus D07
                                               |          |--M. insignis D07
                                               |          |--M. intermontanus W69
                                               |          |--M. stylodontus W69
                                               |          `--M. sumani W69
                                               `--Anchitheriinae C96

Equidae incertae sedis:
  Hippotherium C77
    |--H. affine C77
    |--H. calamarium Cope 1875 C77
    |--H. gratum C77
    |--H. occidentale C77
    |--H. paniense C77
    `--H. speciosum C77
  Protohippus Leidy 1869 C77
    `--P. sejunctus C77
  Plesiohipparion TH03
  Cormohipparion F99
    |--C. goorisi MacFadden & Skinner 1981 F99
    |--C. occidentale Leidy 1856 F99
    `--C. sphenodus Cope 1885 F99
  Eoequus wilsoni Quinn 1955 F99
  Propachynolophus gaudryi RH14
  Eurohippus parvum RH14

Eohippus angustidens (Cope 1875) F02 [=Orohippus angustidens F02, Hyracotherium angustidens F02; incl. *E. validus Marsh 1876 F02, Orohippus cuspidatus Cope 1875 C77, Hyracotherium cuspidatum F02, H. loevii Cope 1877 F02, Orohippus vasacciensis Cope 1875 C77, H. vasacciense F02, Lophiotherium vasacciense C77]

*Protorohippus venticolum (Cope 1881) [=Eohippus venticolum, Hyracotherium vasacciense venticolum] F02

*Type species of generic name indicated

REFERENCES

[B76] Barnes, L. G. 1976. Outline of eastern North Pacific fossil cetacean assemblages. Systematic Zoology 25 (4): 321–343.

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

[M76] MacFadden, B. J. 1976. Cladistic analysis of primitive equids, with notes on other perissodactyls. Systematic Zoology 25 (1): 1–14.

[OB13] O'Leary, M. A., J. I. Bloch, J. J. Flynn, T. J. Gaudin, A. Giallombardo, N. P. Giannini, S. L. Goldberg, B. P. Kraatz, Z.-X. Luo, J. Meng, X. Ni, M. J. Novacek, F. A. Perini, Z. S. Randall, G. W. Rougier, E. J. Sargis, M. T. Silcox, N. B. Simmons, M. Spaulding, P. M. Velazco, M. Weksler, J. R. Wible & A. L. Cirranello. 2013. The placental mammal ancestor and the post-K-Pg radiation of placentals. Science 339: 662–667.

[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.

[TH03] Tedford, R. H., & C. R. Harington. 2003. An Arctic mammal fauna from the Early Pliocene of North America. Nature 425: 388–390.

[W69] Woodburne, M. O. 1969. Systematics, biogeography, and evolution of Cynorca and Dyseohyus (Tayassuidae). Bulletin of the American Museum of Natural History 141 (2): 271–356.