PBDB Taxon

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Hippidion

Mammalia - Perissodactyla - Equidae

Taxonomy

Hippidion was named by Owen (1869). It was considered monophyletic by Prado and Alberdi (1996).

It was corrected as Hippidium by Cope (1881) and Lydekker (1894); it was considered a nomen dubium by Alberdi and Prado (1992) and Alberdi and Prado (1993).

It was assigned to Equinae by Hay (1902) and Gidley (1907); to Equidae by Owen (1869), Cope (1881), Lydekker (1894), Scott (1913) and Carroll (1988); to Pliohippina by Prado and Alberdi (1996); and to Equini by Prothero and Schoch (1989), Kelly (1995) and MacFadden (1998).

Species

H. angulatus, H. devillei (syn. Onohippidium bolivianum, Scelidotherium compressum), H. principale (syn. Onohippidium munizi), H. saldiasi, Hippidium (Plagiohippus), Hippidium bonaerense, Hippidium entrerianum, Hippidium principale (syn. H. compressidens), Onohippidium compressidens, Parahipparion extensus, Parahipparion saldiasi

Synonyms

Parahipparion was named by Ameghino (1904).

It was synonymized subjectively with Hippidion by Prothero and Schoch (1989).

It was assigned to Equidae by Oliver Schneider (1926).
Onohippidium was named by Moreno (1891). It is not extant.

It was considered an invalid subgroup of Pliohippina by Prado and Alberdi (1996); it was synonymized subjectively with Hippidion by Alberdi and Prado (1993) and Dos Santos Avilla et al. (2015).

It was assigned to Equidae by Moreno (1891), Lydekker (1894), MacFadden and Skinner (1979), Carroll (1988), MacFadden (1997) and Kelly (1998); and to Equini by Prothero and Schoch (1989), Kelly (1995) and MacFadden (1998).
Onohippidion was named by Filhol (1888). It is not extant.

It was synonymized subjectively with Onohippidium by McKenna and Bell (1997).

It was assigned to Equidae by Rusconi (1934).

Synonymy list

Year	Name and author
1869	Hippidion Owen
1881	Hippidium Cope p. 400
1888	Onohippidion Filhol
1891	Onohippidium Moreno
1894	Hippidium Lydekker p. 74
1894	Onohippidium Lydekker p. 77
1902	Hippidion Hay p. 618
1904	Parahipparion Ameghino
1907	Hippidion Gidley p. 867
1913	Hippidion Scott p. 290
1926	Parahipparion Oliver Schneider p. 149
1934	Onohippidion Rusconi p. 27
1979	Onohippidium MacFadden and Skinner p. 3
1988	Hippidion Carroll
1988	Onohippidium Carroll
1989	Hippidion Prothero and Schoch p. 532
1989	Onohippidium Prothero and Schoch p. 532
1995	Hippidion Kelly p. 25
1995	Onohippidium Kelly p. 25
1996	Hippidion Prado and Alberdi p. 676
1997	Onohippidium MacFadden
1998	Onohippidium Kelly
1998	Hippidion MacFadden p. 551
1998	Onohippidium MacFadden p. 552

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Rank	Name	Author
kingdom	Animalia	()
—	Bilateria
—	Eubilateria	Ax 1987
—	Deuterostomia
phylum	Chordata	Haeckel 1874
subphylum	Vertebrata
superclass	Gnathostomata
—	Osteichthyes	()
subclass	Sarcopterygii	()
subclass	Dipnotetrapodomorpha	(Nelson 2006)
subclass	Tetrapodomorpha	()
—	Tetrapoda
—	Reptiliomorpha
—	Anthracosauria
subclass	Amphibiosauria	Kuhn 1967
—	Cotylosauria	()
—	Amniota
subclass	Synapsida
—	Therapsida	()
infraorder	Cynodontia	()
—	Mammaliamorpha
—	Mammaliaformes

Rank	Name	Author
class	Mammalia
—	Theriamorpha	(Rowe 1993)
—	Theriiformes	()
—	Trechnotheria
—	Cladotheria
—	Zatheria
subclass	Tribosphenida	()
subclass	Theria
—	Eutheria	()
—	Placentalia
—	Boreoeutheria
—	Laurasiatheria
—	Scrotifera
—	Euungulata
—	Panperissodactyla
superorder	Perissodactylamorpha
order	Perissodactyla	()
superfamily	Equoidea
family	Equidae
subfamily	Equinae
tribe	Equini
genus	Hippidion	Owen 1869

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

G. †Hippidion Owen 1869

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†Hippidion angulatus Ameghino 1889

†Hippidion devillei Gervais 1855

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Invalid names: Onohippidium bolivianum Philippi 1893 [synonym]

†Hippidion principale Lund 1846

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Invalid names: Onohippidium munizi Moreno 1891 [synonym]

†Hippidion saldiasi Roth 1899

Subg. †Hippidium (Plagiohippus) Ameghino 1908

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†Plagiohippus chapalmalensis Ameghino 1908

†Hippidium bonaerense Ameghino 1907

†Hippidium entrerianum Ameghino 1886

†Hippidium principale Lund 1846

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Invalid names: Hippidion compressidens Ameghino 1889 [synonym]

Invalid names: Onohippidium Moreno 1891 [synonym], Parahipparion Ameghino 1904 [synonym]

Diagnosis

Reference	Diagnosis
B. J. MacFadden and M. F. Skinner 1979 (Onohippidium)	Horse with nasal notch that lies as far anterior as P3-P4 and as far posterior as the orbit. Nasal bones not re- tracted and remain elongate splints. Well- developed dorsal lacrimal fossa and no ven- tral malar fossa. Incisors with cement-filled cups (infidibula). Protocone oval to rounded with weak preprotoconal groove and well- developed postprotoconal valley. Lower cheek teeth with either shallow ectoflexids (externomedial valleys) and isthmuses in the permanent premolars or deep ectoflexids in the deciduous premolars and molars. Very simple enamel plications. Monodacty! metapodials.