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Equus (horse)

Mammalia - Perissodactyla - Equidae


The genus Equus includes many extinct species in addition to the living domestic horse, zebras, and asses. It originated in North America and emigrated to the Old World during the Pliocene. In the 1920s a spectacular mass mortality assemblage of the primitive species Equus simplicidens was found at the Gidley Horse Quarry in Idaho. Before the end-Pleistocene megafaunal mass extinction several species of horses lived in North America. Pleistocene horses fossils are very common, but their taxonomy is still poorly resolved because many of the older species names were based on poor type specimens.

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Synonymy list
YearName and author
1758Equus Linnaeus p. 73
1762Onager Brisson
1822Asinus Gray
1825Asinus Gray p. 342
1846Asinus Owen
1848Equus Owen p. 139
1858Asinus africanus Fitzinger
1860Equus Leidy p. 100
1861Equus taeniopus Heuglin
1881Equus Cope p. 400
1884Asinus Noack
1884Asinus taeniopus Noack
1892Tomolabis Cope p. 125
1893Equus semiplicatus Cope p. 80
1901Equus semiplicatus Gidley p. 129 fig. 20
1902Equus Hay p. 621
1902Equus semiplicatus Hay p. 624
1907Equus Gidley p. 867
1913Neohippus Abel
1916Equus (Asinus) Lydekker
1916Equus asinus taeniopus Lydekker
1924Plesippus Matthew p. 2
1926Equus Schneider p. 149
1930Plesippus Gidley
1930Kolpohippus van Hoepen
1930Kraterohippus van Hoepen
1930Sterrohippus van Hopen
1935Asinus Dollman
1935Equus Schultz and Howard p. 285
1940Equus Stirton p. 194
1942Asinus Hopwood
1945Asinus Harper
1955Equus Hibbard p. 51
1955Asinus Quinn p. 52
1955Equus Quinn p. 58
1957Onager Quinn p. 10
1957Onager semiplicatus Quinn p. 10
1957Asinus Quinn p. 27
1957Equus Quinn p. 27
1958Asinus Quinn
1959Asinus Mooser
1961Allozebra Trumler
1961Asinus Trumler
1965Plesippus Hibbard and et al.
1970Equus (Plesippus) Howe
1970Plesippus Shotwell
1972Equus (Amerhippus) Skinner p. 118
1980Equus Kurten and Anderson p. 285
1981Equus Thurmond and Jones p. 185
1988Equus Carroll
1989Equus Prothero and Schoch p. 532
1995Equus Capasso Barbato and Gliozzi p. 246
1995Equus (Plesippus) Forsten and Eisenmann p. 88
1995Equus Kelly p. 19
1995Plesippus Repenning et al.
1996Equus Prado and Alberdi p. 676
1998Equus MacFadden p. 552
2004Equus (Amerhippus) Zurita et al.
2005Equus Cisneros p. 249
2006Equus (Amerhippus) Rincón et al.
2006Equus Salles et al. p. 8
2018Equus Eshelman et al. p. 8

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phylumChordataHaeckel 1847
subclassDipnotetrapodomorpha(Nelson 2006)
subfamilyEquinaeSteinmann and Döderlein 1890

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.

J. H. Quinn 1955Large horses with complex permanent upper cheek teeth; styles of ectoloph high and thick, valleys deep and concave; protocones elongate and trans- versely compressed, internally concave but not as markedly as in Asinus; lower per- manent teeth with long, crescentic meta- conids and metastylids, intervening valleys U-shaped; lower molars with short median valleys not penetrating between the reen- trants of the flexids as deeply as in Hippo- tigris. In Old World species the median valley reaches the reentrants of the flexids but does not penetrate as deeply as in Hip- potigris; lower milk dentition without parastylids and hypostylids.
J. H. Quinn 1955 (Asinus)Lower milk dentition with parastylids and hypostylids weak or absent; lower permanent dentition with anterior border of metaflexid produced outward in a deep sharp angle exceeding either Equus or Hippotigris; metaconid directed inward and then forward, elongate and flattened internally, metastylid deflected, restricted, and rounded, inter- vening valley V-shaped as in the zebras but less deeply so; entoconid rounded and restricted; hylpoconulid prominent and with a hypostylid; pli caballinid present; median valley of molars variably shortened and not protruding beyond the reentrants of the flexids which form a short narrow commissure; upper permanent teeth with small fossettes; small enamel inflections; protocones excessively flat- tened and concave internally in late
species; metapodials slender.
J. H. Quinn 1957 (Asinus)Upper permanent teeth with square outline, small fossettes, protocones shorter than in Onager and teeth less hypsodont; lower permanent dentition, metaconid tends to be deflected inward, then forward, metastylid deflected and short tending to be nearly rounded; inter- vening valley V-shaped as in Hippotigris but less deeply so, no parastylid, pli caballinid present, hypoconulid prominent and with a hypostylid, median valley of molars not protruding between re-entrants of the flexids (except in very early stage of wear); lower milk dentition with parastylids and hypostylids weak or absent; metatarsals short and stout but less so than in Equus
J. H. Quinn 1957 (Onager)Size range equal to Equus; pattern of upper cheek teeth more complex, protocones elongated, hypoconal groove of premolars tends to be partly closed, third molar less modified than in Equus or Asinus; lower molars with median valley shorter than in most species of Equus; upper and lower teeth equalling or sur- passing Equus in hypsodonty and appreciably more hypsodont than Asinus; metapodials long and more slender than in Equus, longer and more slender than in A sinus.