Skull of Hyracotherium leporinum, from Owen (1841).

Belongs within: Cetferungulata.
Contains: Chalicotheriidae, Ceratomorpha, Equidae.

The Perissodactyla include the odd-toed hoofed mammals: horses, tapirs and rhinoceroses, as well as their fossil relatives the chalicotheres and brontotheres. Perissodactyls are relatively large herbivorous mammals with hind-gut fermenting digestive systems.

Synapomorphies (from Hooker & Dashzeveg 2004): Upper molar paraconule situated distinctly more mesially than protocone, facet 2A occupying paraconule and part of preprotocrista, notched preprotocrista mesiobuccally directed towards paraconule, lower molar metaconid widely twinned with tips bearing facet 2A; upper molar metaconule distinctly mesial of line drawn between metacone and hypocone, lower molar hypoconulid separated from and distal of crest joining hypoconid and entoconid, M3 with hypocone; upper molar parastyle large; M3 not smaller than M2, M3 larger than M2; upper molars with metaconal fold not joined to metaconule; upper molar metaloph and lower molar hypolophid, especially on M3, oblique.

<==Perissodactyla [Mesaxonia, Selenida]
    |  i. s.: Helaletes F02
    |         Symborodon C76
    |         Orotherium Marsh 1872 C76
    |           |--O. cristonense Cope 1876 C76
    |           |--O. laevii C76
    |           `--O. vintanum Marsh 1872 C76
    |         Oligotomus C76
    |         Dolichorhinus JJ84
    |         Brontops JJ84
    |--Brontotheriidae [Brontotherioidea, Titanotheriomorpha] HD04
    |    |  i. s.: Danjiangia HD04
    |    |         Lambdotherium popoagicum HD04
    |    |--Embolotheriinae WW97
    |    |--Rhinotitan [Epimanteoceratinae] WW97
    |    |    `--R. mongoliensis WW97
    |    `--Metatelmatheriinae WW97
    |         |--Desmatotitan WW97
    |         |--Hyotitan WW97
    |         |--Acrotitan WW97
    |         |--Arctotitan WW97
    |         |--Qufutitan Wang & Wang 1997 WW97
    |         |    `--*Q. zhoui Wang & Wang 1997 WW97
    |         `--Metatelmatherium WW97
    |              |--M. cristatum WW97
    |              `--M. ultimum WW97
    `--Lophodontomorpha [Isectolophidae, Moropomorpha, Tapiromorpha] HD04
         |  i. s.: Palaesyops F02
         |--Orientolophus Ting 1993 HD04
         |    |--*O. hengdongensis Ting 1993 HD04
         |    `--O. namadicus (Dashzeveg 1979) [=Homogalax namadicus] HD04
         |--Ancylopoda HD04
         |    |--Cardiolophus radinskyi Gingerich 1991 HD04
         |    `--+--Homogalax F02
         |       |    |--H. protapirinus [=Systemodon protapirinus] F02
         |       |    `--H. wutuensis HD04
         |       `--+--Isectolophus F02
         |          `--Chalicotherioidea HD04
         |                |--Protomoropus Hooker & Dashzeveg 2004 HD04
         |                |    `--*P. gabuniai (Dashzeveg 1979) [=Hyracotherium gabuniai, Orientolophus gabuniai] HD04
         |                `--+--Chalicotheriidae F02
         |                   `--Lophiodontidae HD04
         |                        |--Paleomoropus jepseni Radinsky 1964 HD04
         |                        `--+--Lophiaspis maurettei Depéret 1910 HD04
         |                           `--Lophiodon Cuvier 1822 [incl. Saurornis Fischer 1967] M02
         |                                `--*Saurornis’ matthesi Fischer 1967 M02
         `--Euperissodactyla HD04
              |--Ceratomorpha HD04
              `--Equoidea [Hippomorpha] 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
                         `--+--Hallensia mathewsi F02
                            `--+--Hyracotherium Owen 1841 F02
                               |    |--*H. leporinum Owen 1841 F02
                               |    |--H. agile (Marsh 1873) [=Orohippus agilis] C76
                               |    |--H. procyoninum (Cope 1872) [=Helotherium procyoninum] C76
                               |    |--H. siderolithicum C76
                               |    `--H. sylvaticum C76
                               `--Palaeotheriidae F02
                                    |--Propachynolophus F02
                                    |--Anchilophus F02
                                    |--Plagiolophus F02
                                    |--Palaeotherium C96
                                    `--Propalaeotherium C96

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

*Type species of generic name indicated


[C96] Campbell, N. A. 1996. Biology (4th ed.) The Benjamin/Cummings Publishing Company, Inc.: Menlo Park (California).

[C76] Cope, E. D. 1876. 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.

[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.

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

[JJ84] Janis, C., & P. J. Jarman. 1984. The hoofed mammals. In All the World’s Animals: Hoofed Mammals (D. Macdonald, ed.) pp. 28-39. Torstar Books: New York.

[M02] Mlíkovský, J. 2002. Cenozoic Birds of the World. Part 1: Europe. Ninox Press: Praha.

Owen, R. 1841. Description of the fossil remains of a mammal (Hyracotherium leporinum) and of a bird (Lithornis vulturinus) from the London Clay. Transactions of the Geological Society of London, series 2, 6: 203-208, pl. 21.

[WW97] Wang Y. & Wang J. 1997. A new brontothere from late Middle Eocene of Qufu, Shandong. Vertebrata PalAsiatica 35 (1): 68-77.

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