Equoidea

Reconstructed skeleton of Palaeotherium magnum, by Jean Albert Gaudry.

Belongs within: Perissodactyla.
Contains: Equidae.

The Equoidea are a clade of perissodactyls uniting the horses (Equidae) with the fossil Palaeotheriidae from the Eocene and Oligocene of Eurasia.

Synapomorphies (from Hooker & Dashzeveg 2004): Upper molar metaconule large; P³ with trigon broader, protoloph stronger, paraconule (unless subsumed by protoloph) and metaconid much larger and better defined, but smaller than protocone and protoconid respectively; lower M_1–2 distal cingulum lingual of hypoconulid absent.

<==Equoidea [Hippomorpha, Hyracotheriinae] HD04
    |--+--Cymbalophus Hooker 1984 HD04, F02
    |  |    `--*C. cuniculus (Owen 1842) [=Hyracotherium cuniculus] F02
    |  `--Systemodon Cope 1881 F02
    |       |--*S. tapirinus (Cope 1875) (see below for synonymy) F02
    |       `--S. etsagicus (Cope 1884) [=Hyracotherium angustidens etsagicum] F02
    `--+--Sifrhippus Froehlich 2002 HD04, F02
       |    `--*S. sandrae (Gingerich 1989) [=Hyracotherium sandrae] F02
       `--+--Equidae HD04
          `--Palaeotheriidae HD04
               |  i. s.: Anchilophus F02
               |--Hyracotherium Owen 1841 F02
               |    |--*H. leporinum Owen 1841 F02
               |    |--H. agile (Marsh 1873) [=Orohippus agilis] C77
               |    |--H. procyoninum (Cope 1872) [=Helotherium procyoninum] C77
               |    |--H. siderolithicum C77
               |    `--H. sylvaticum C77
               `--+--Propalaeotherium parvulum RH14, S12
                  `--+--+--Plagiolophus annectens RH14
                     |  `--Leptolophus nouleti RH14
                     `--Palaeotherium Cuvier 1804 RH14, H07
                          |--P. castrense D07
                          |--P. crassum D07
                          |--P. curtum D07
                          |--P. lautricense D07
                          |--P. magnum Cuvier 1804 H07
                          |--P. medium D07
                          `--P. ruetimeyeri D07

Systemodon tapirinus (Cope 1875) [=Hyracotherium tapirinum, Orohippus tapirinus; incl. H. cristatum Wortman 1896] F02

*Type species of generic name indicated

REFERENCES

[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.

[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.

[H07] Hooker, J. J. 2007. Bipedal browsing adaptations of the unusual Late Eocene-earliest Oligocene tylopod Anoplotherium (Artiodactyla, Mammalia). Zoological Journal of the Linnean Society 151 (3): 609–659.

[HD04] Hooker, J. J., & D. Dashzeveg. 2004. The origin of chalicotheres (Perissodactyla, Mammalia). Palaeontology 47 (6): 1363–1386.

[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.

[S12] Schaal, S. 2012. Messel Pit fossil site—the legacy of the environment and life of the Eocene. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 225–236. Springer.