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Orohippus Temporal range: early to middle Eocene
Skeleton of Orohippus pumillus at the Smithsonian Museum of Natural History.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Equidae
Genus:	†Orohippus Marsh, 1872
Type species
†Orohippus pumillus
Species
†O. agilis †O. major †O. progressus †O. proteros †O. pumillus †O. sylvaticus

Orohippus (from the Greek ὄρος óros, 'mountain' and ἵππος híppos, 'horse') is an extinct equid that lived in the Eocene (about 50 million years ago).

Description

It is believed to have evolved from equids such as Eohippus, as the earliest evidence for Orohippus appears about 2 million years after the first appearance of Eohippus. The anatomical differences between the two are slight: they were the same size, but Orohippus had a slimmer body, a more elongated head, slimmer forelimbs and longer hind legs, all of which are characteristics of a good jumper. Its teeth were brachydont in height, but the development of flattened surfaces and shearing lophs on their molars suggests they were more a browser than a frugivore. The outer toes of Eohippus are no longer present in Orohippus, hence on each forelimb there were four fingers (toes) and on each hind leg three toes.

Species of Orohippus has also been referred to Protorohippus.

See also

• Evolution of the horse
• Horse

Notes

1. MacFadden, 1998, p.554
2. MacFadden, 1998, p.543
3. "Glossary. American Museum of Natural History". Archived from the original on 20 November 2021.
4. Kitts, D. B. 1957. A Revision of the Genus Orohippus (Perissodactyla, Equidae). American Museum Novelties, 1864:1–40.

References

• MacFadden, B.J., 1998. Equidae. pp. 537–559 in C.M. Janis, K.M. Scott, and L.L. Jacobs (eds.) Evolution of Tertiary Mammals of North America Cambridge University Press, Cambridge.
• Orohippus, Index Fossils and the Tertiary
• The Evolution of the Horse
• National Center for Science Education

v t e Perissodactyla
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Perissodactyla
Perissodactyla Incertae sedis †Ghazijhippus †Mesolambdolophus †Olbitherium †Anthracobunia Radinskya †Anthracobunidae Anthracobune Hsanotherium Jozaria Obergfellia †Cambaytheriidae Cambaytherium Kalitherium Nakusia Perissobune †Brontotheriidae See Brontotheriidae Equoidea †Cymbalophus †Hallensia †Pliolophus †Systemodon Equidae See Equidae †Palaeotheriidae †Pachynolophinae Anchilophus Bepitherium Eurohippus Hyracotherium Lijiangia Lophiohippus Lophiotherium Metanchilophus Orolophus Pachynolophus Paranchilophus Propalaeotherium Qianohippus †Palaeotheriinae Cantabrotherium Iberolophus Idiodontherium Leptolophus Mekodontherium Metaplagiolophus Palaeotherium Paraplagiolophus Plagiolophus Pseudopalaeotherium †Hyopsodontidae? Aletodon Chacomylus Dorraletes Haplaletes Haplomylus Hyopsodus Litomylus Louisina Monshyus Paratricuspiodon Paschatherium Phenacodaptes Tricuspiodon †Phenacodontidae? Tetraclaenodon †Meniscotheriinae Ectocion Meniscotherium †Phenacodontinae Almogaver Copecion Eodesmatodon Lophocion Phenacodus Tapiromorpha See below↓
Tapiromorpha Incertae sedis †Cambaylophus †Skopaiolophus †Isectolophidae Chowliia Gandheralophus Karagalax Meridiolophus Orientolophus Sastrilophus †Homogalaxinae Homogalax †Isectolophinae Isectolophus Schizolophodon †Ancylopoda See Ancylopoda Ceratomorpha Tapiroidea †Deperetellidae Bahinolophus Deperetella Irenolophus Teleolophus †Helaletidae Colodon Dilophodon Helaletes Heptodon Heteraletes Paracolodon Plesiocolopirus Thuliadanta? Vastanolophus Tapiridae †Eotapirus †Miotapirus †Nexuotapirus †Paratapirus †Plesiotapirus †Protapirus †Tapiravus Tapirus Rhinocerotoidea See below↓
Rhinocerotoidea Rhinocerotoidea sensu lato †Breviodon †Fouchia †Minchenoletes †Siamolophus †Triplopus †Yimengia †Indolophidae Indolophus Rhinocerotoidea sensu stricto †Selenaletes †Hyrachyidae Hyrachyus †Eggysodontidae Allacerops Eggysodon Guangnanodon Proeggysodon †Hyracodontidae Ardynia Ephyrachyus Epitriplophus Hyracodon Prohyracodon Rhodopagus Triplopides †Amynodontidae Amynodontopsis Armania Cadurcotherium Caenolophus Huananodon Hypsamynodon Procadurcodon Rostriamynodon Teilhardia †Amynodontinae Amynodon †Cadurcodontini Cadurcodon Lushiamynodon Sharamynodon Sianodon †Metamynodontini Gigantamynodon Megalamynodon Metamynodon Paramynodon Zaisanamynodon †Paraceratheriidae †Forstercooperiinae Forstercooperia Gobicerops Pappaceras †Paraceratheriinae Aralotherium Dzungarotherium Juxia Paraceratherium Urtinotherium Rhinocerotidae See below↓
Rhinocerotidae Rhinocerotidae †Amphicaenopus †Epiaceratherium †Guixia †Teletaceras †Uintaceras †Woodoceras †Aceratheriinae Aceratherium Acerorhinus Alicornops Aphelops Chilotheridium Chilotherium Floridaceras Galushaceras Hoploaceratherium Mesaceratherium Peraceras Persiatherium Plesiaceratherium Ronzotherium Shansirhinus Sinorhinus Subchilotherium †Elasmotheriinae Gulfoceras Victoriaceros †Diceratheriini Diceratherium Penetrigonias Skinneroceras Subhyracodon Trigonias †Elasmotheriini Bugtirhinus Caementodon Elasmotherium Hispanotherium Iranotherium Kenyatherium Meninatherium Menoceras Ninxiatherium Ningxiatherium Ougandatherium Parelasmotherium Procoelodonta Sinotherium Tongxinotherium Rhinocerotinae †Dromoceratherium †Lartetotherium †Molassitherium †Protaceratherium †Teleoceratini Aprotodon Brachydiceratherium Brachypotherium Diaceratherium Prosantorhinus Shennongtherium Teleoceras Rhinocerotina Dicerorhinini †Coelodonta Dicerorhinus †Dihoplus †Pliorhinus †Stephanorhinus Dicerotini Ceratotherium Diceros †Miodiceros †Paradiceros Rhinocerotini †Gaindatherium †Nesorhinus Rhinoceros †Rusingaceros

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