PBDB Taxon

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Orohippus

Mammalia - Perissodactyla - Equidae

Taxonomy

Orohippus was named by Marsh (1872).

It was assigned to Hyracotheriinae by Hay (1902) and MacFadden (1998); and to Equidae by Marsh (1872), Scott (1913), Stirton (1940), Kitts (1957), Carroll (1988), Prothero and Schoch (1989) and Froehlich (2002).

Species

O. (Aminippus), O. agilis, O. major, O. progressus, O. proteros, O. pumilus (syn. Helotherium procyoninum, O. typicus, Hyracotherium osbornianum, O. atavus, Oligotomus cinctus, Lophiotherium ballardi), O. sylvaticus (syn. Orotherium uintanum)

Synonyms

Orohippus (Aminippus) was named by Granger (1908).

It was considered an invalid subgroup of Orohippus by Kitts (1957).

It was assigned to Orohippus by Granger (1908).
Helohippus was named by Marsh (1892). Its type is Lophiodon pumilus.

It was synonymized subjectively with Pachynolophus by Roger (1896); it was synonymized subjectively with Orohippus by Granger (1908), Stirton (1940), Kitts (1957) and Gazin (1976).

It was assigned to Hyracotheriinae by Hay (1902).
Helotherium was named by Cope (1872).

It was synonymized subjectively with Hyracotherium by Cope (1877) and Matthew (1899); it was synonymized subjectively with Lambdotherium by Cope (1884); it was synonymized subjectively with Orohippus by Cope (1873), Marsh (1874), Hay (1902), Granger (1908), Osborn (1929) and Kitts (1957).
Oligotomus was named by Cope (1873).

It was synonymized subjectively with Pliolophus by Cope (1884); it was synonymized subjectively with Pachynolophus by Roger (1896); it was synonymized subjectively with Orohippus by Wortman (1896), Hay (1902), Granger (1908) and Kitts (1957).

Synonymy list

Year	Name and author
1872	Helotherium Cope
1872	Orohippus Marsh
1873	Oligotomus Cope
1892	Helohippus Marsh p. 353
1902	Helohippus Hay p. 611
1902	Orohippus Hay p. 611
1908	Orohippus (Aminippus) Granger p. 254
1913	Orohippus Scott p. 290
1940	Orohippus Stirton p. 168
1957	Orohippus Kitts p. 3
1988	Orohippus Carroll
1989	Orohippus Prothero and Schoch p. 531
1998	Orohippus MacFadden p. 543
2002	Orohippus Froehlich p. 151

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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

Rank	Name	Author
—	Mammaliaformes
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
genus	Orohippus

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. †Orohippus Marsh 1872

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†Orohippus agilis Marsh 1873

†Orohippus major Marsh 1874

†Orohippus progressus Granger 1908

†Orohippus proteros Korth and Evander 1982

†Orohippus pumilus Marsh 1871

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Invalid names: Helotherium procyoninum Cope 1871 [synonym], Hyracotherium osbornianum Cope 1883 [synonym], Lophiotherium ballardi Marsh 1871 [synonym], Oligotomus cinctus Cope 1873 [synonym], Orohippus atavus Granger 1908 [synonym], Orohippus typicus Granger 1908 [synonym]

†Orohippus sylvaticus Leidy 1870

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Invalid names: Orotherium uintanum Marsh 1872 [synonym]

Invalid names: Helohippus Marsh 1892 [synonym], Helotherium Cope 1872 [synonym], Oligotomus Cope 1873 [synonym], Orohippus (Aminippus) Granger 1908 [invalid subgroup]

Diagnosis

Reference	Diagnosis
D. B. Kitts 1957	P3 and P4 with four major cusps in al species and fuly molariform in advanced species. Mesostyle on molars in all species and on P3 and P4 in advanced species. Upper molars with well-developed lophs but with intermediate cusps detectable. Ectoloph on molars V-shaped in crown view in al species and on P3 and P4 of advanced species. P4 molariform. Mesolophid sharply oblique. Digits I and V absent in pes