PBDB Taxon

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Morphology	Ecology and taphonomy	External Literature Search	Age range and collections

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. O. atavus, Lophiotherium ballardi, O. typicus, Helotherium procyoninum, Oligotomus cinctus, Hyracotherium osbornianum), 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

Measurements

No measurements are available

Composition:

phosphaticsubp

Environment:

terrestrialsubc

Locomotion:

actively mobilec

Life habit:

ground dwellingf

Diet:

browserf

Reproduction:

viviparoussubc

Created:

2005-06-08 10:11:09

Modified:

2005-08-31 16:55:50

Source: f = family, subc = subclass, c = class, subp = subphylum

References: Nowak 1991, Carroll 1988, Ji et al. 2002, Lillegraven 1979, Hendy et al. 2009

Age range: base of the Wasatchian to the top of the Early/Lower Uintan or 55.80000 to 39.70000 Ma

Collections (69 total)

Time interval	Ma	Country or state	Original ID and collection number
Lostcabinian	55.8 - 50.3	USA (Wyoming)	O. sp. (15901 15945)
Wasatchian	55.8 - 50.3	USA (Wyoming)	O. proteros (15454 15902) O. sp. (15942)
Bridgerian	50.3 - 46.2	USA (Wyoming)	Lophiodon pumilus (16281) O. atavus (16205) O. major (16284) O. osbornianus (16136) O. progressus (16448) O. pumilus (16089 16094 16105 16107 16108 16114 16116 16219 16227 16228 16232 16262 16263 16269 16291 16300 16302 16303 16306 16309 16315 16321 16330 16336 16339 16353 16355 16441 16504) O. sp. (15837 16137 16138 16139 16140 16203 16207 16209 16211 16223 16244 16254 16294 16415 16418 16431 16432 16438 16444 16481 16489 16499 16502 16647 129895 202161) O. sylvaticus (16406)
Bridgerian	50.3 - 46.2	USA (Colorado)	O. sylvaticus (16251)
Middle Eocene	47.8 - 37.71	USA (Wyoming)	O. agilis (81455)
Early/Lower Uintan	46.2 - 39.7	USA (Colorado)	O. sylvaticus (16623)