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Equus (horse)

Discussion

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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Taxonomy

Equus was named by Linnaeus (1758) [type Eurasian E. caballus]. It is extant. Its type is Equus caballus.

It was assigned to Bellua by Linnaeus (1758); to Pachydermata by Owen (1844); to Perissodactyla by Owen (1848); to Solipedia by Leidy (1860); to Equinae by Hay (1902), Gidley (1907), Koufos (1992); to Pliohippina by Prado and Alberdi (1996); to Equini by Quinn (1955), Quinn (1957), Prothero and Schoch (1989), Kelly (1995), MacFadden (1998), Alberdi et al. (2014); and to Equidae by Leidy (1873), Cope (1881), Scott (1913), Oliver Schneider (1926), Schultz and Howard (1935), Stirton (1940), Hibbard (1955), Kurten and Anderson (1980), Thurmond and Jones (1981), Carroll (1988), Capasso Barbato and Gliozzi (1995), Wilson and Reeder (2005), Cisneros (2005), Salles et al. (2006), Eshelman et al. (2018), Parray et al. (2022), Eshelman et al. (2025).

Synonyms

Neohippus was named by Abel (1913).

It was synonymized subjectively with Equus by Prothero and Schoch (1989), Rincón et al. (2006).
Tomolabis was named by Cope (1892).

It was synonymized subjectively with Equus by Hay (1902).
Equus taeniopus was named by Heuglin (1861). It is extant.

It was recombined as Asinus taeniopus by Noack (1884); it was recombined as Equus asinus taeniopus by Lydekker (1916); it was considered a nomen dubium by Groves and Smeenk (2007).
Asinus africanus was named by Fitzinger (1858) [non Asinus africanus Heuglin and Fitzinger 1866]. It is extant.

It was considered a nomen nudum by Groves and Smeenk (2007).
Kraterohippus was named by van Hoepen (1930).

It was synonymized subjectively with Equus by Prothero and Schoch (1989).
Kolpohippus was named by van Hoepen (1930).

It was synonymized subjectively with Equus by Prothero and Schoch (1989).
Sterrohippus was named by van Hopen (1930).

It was synonymized subjectively with Equus by Prothero and Schoch (1989).
Haringtonhippus was named by Heintzman et al. (2017). It was considered monophyletic by Heintzman et al. (2017).

It was synonymized subjectively with Equus by Barrón-Ortiz et al. (2019).

It was assigned to Equini by Heintzman et al. (2017).
Allozebra was named by Trumler (1961).

It was synonymized subjectively with Equus by Mooser and Dalquest (1975).
Amerhippus was named by Hoffstetter (1950). Its type is Equus andium.

It was reranked as Equus (Amerhippus) by Skinner (1972), Zurita et al. (2004), Rincón et al. (2006); it was considered an invalid subgroup of Equus by Orlando et al. (2008).

It was assigned to Equus by Skinner (1972), Zurita et al. (2004), Rincón et al. (2006).
Asinus was named by Gray (1822) [type African Equus asinus, senior synonym of Asinus vulgaris Gray 1822; also said to be 1824]. Its type is Equus asinus.

It was reranked as Equus (Asinus) by Lydekker (1916); it was synonymized subjectively with Equus by von Meyer (1832), Sclater (1884), Thomas (1884), Pavlow (1890), Scott (1895), Osborn (1929), Schultz (1938), Popov (1939), McGrew (1944), Edinger (1948), Azzaroli (1966), Groves and Willoughby (1981), Prothero and Schoch (1989).

It was assigned to Equidae by Gray (1822), Gray (1825); to Equus by Lydekker (1916); and to Equini by Quinn (1955), Quinn (1957).
Equus (Parastilidequus) was named by Mooser and Dalquest (1975).

It was considered an invalid subgroup of Equus by Downs and Miller (1994).

It was assigned to Equus by Mooser and Dalquest (1975).
Equus leidyi was named by Hay (1913). Its type specimen is Wagner Free Institute of Science 4086, a tooth, and it is a 3D body fossil.

It was synonymized subjectively with Equus fraternus by Sellards (1940), Lundelius (1972), Hulbert and Morgan (1989); it was considered a nomen vanum by Savage (1951).
Equus parastylidens was named by Mooser (1959). Its type locality is Cedazo, which is in an Irvingtonian terrestrial horizon in the Tacubaya Formation of Mexico.

It was recombined as Equus (Parastilidequus) parastylidens by Mooser and Dalquest (1975); it was considered a nomen dubium by Downs and Miller (1994).
Equus semiplicatus was named by Cope (1893).

It was synonymized subjectively with Equus intermedius by Matthew (1903); it was recombined as Onager semiplicatus by Quinn (1957); it was synonymized subjectively with Equus conversidens by Kurten and Anderson (1980); it was considered a nomen dubium by Dalquest and Schultz (1992), Hulbert (1995).
Hippotherium princeps was named by Leidy (1890).

It was recombined as Hipparion princeps by Roger (1896); it was synonymized subjectively with Equus complicatus by Hay (1902); it was recombined as Neohipparion princeps by Gidley (1907); it was synonymized subjectively with Equus fraternus by Osborn (1918); it was considered a nomen dubium by Lucas (1896), Simpson (1930), Macdonald (1992).
Onager was named by Brisson (1762) [attributed to Brisson 1780; credited as author because Brisson is unavailable]. It is extant.

It was synonymized subjectively with Equus by Groves and Willoughby (1981), Prothero and Schoch (1989).

It was assigned to Equini by Quinn (1957).

Synonymy list

Year	Name and author
1758	Equus Linnaeus p. 73
1762	Onager Brisson
1822	Asinus Gray
1825	Asinus Gray p. 342
1844	Equus Owen p. 230
1846	Asinus Owen
1848	Equus Owen p. 139
1858	Asinus africanus Fitzinger
1860	Equus Leidy p. 100
1861	Equus taeniopus Heuglin
1873	Equus Leidy p. 321
1881	Equus Cope p. 400
1884	Asinus Noack
1884	Asinus taeniopus Noack
1890	Hippotherium princeps Leidy p. 182
1892	Tomolabis Cope p. 125
1893	Equus semiplicatus Cope p. 80
1896	Hippotherium princeps Leidy and Lucas p. 49
1896	Hipparion princeps Roger
1901	Equus semiplicatus Gidley p. 129 fig. 20
1902	Equus Hay p. 621
1902	Equus semiplicatus Hay p. 624
1907	Equus Gidley p. 867
1907	Neohipparion princeps Gidley p. 910
1913	Neohippus Abel
1913	Equus leidyi Hay p. 572
1913	Equus Scott p. 291
1916	Equus (Asinus) Lydekker
1916	Equus asinus taeniopus Lydekker
1926	Equus Oliver Schneider p. 149
1930	Kolpohippus van Hoepen
1930	Kraterohippus van Hoepen
1930	Sterrohippus van Hopen
1935	Asinus Dollman
1935	Equus Schultz and Howard p. 285
1940	Equus Stirton p. 194
1942	Asinus Hopwood
1945	Asinus Harper
1955	Equus Hibbard p. 51
1955	Asinus Quinn p. 52
1955	Equus Quinn p. 58
1957	Onager Quinn p. 10
1957	Onager semiplicatus Quinn p. 10
1957	Asinus Quinn p. 27
1957	Equus Quinn p. 27
1958	Asinus Quinn
1959	Asinus Mooser
1959	Equus parastylidens Mooser
1961	Allozebra Trumler
1961	Asinus Trumler
1972	Equus (Amerhippus) Skinner p. 118
1975	Equus (Parastilidequus) Mooser and Dalquest p. 807
1975	Equus (Parastilidequus) parastylidens Mooser and Dalquest p. 807
1980	Equus Kurten and Anderson p. 285
1980	Equus parastylidens Kurten and Anderson p. 287
1981	Equus Thurmond and Jones p. 185
1988	Equus Carroll
1989	Equus Prothero and Schoch p. 532
1992	Equus Koufos
1995	Equus Capasso Barbato and Gliozzi p. 246
1995	Equus leidyi Hulbert, Jr.
1995	Equus Kelly p. 19
1996	Equus Prado and Alberdi p. 676
1998	Equus MacFadden p. 552
2004	Equus (Amerhippus) Zurita et al.
2005	Equus Cisneros p. 249
2005	Equus Wilson and Reeder
2006	Equus (Amerhippus) Rincón et al.
2006	Equus Salles et al. p. 8
2014	Equus Alberdi et al.
2017	Haringtonhippus Heintzman et al. p. 5
2018	Equus Eshelman et al. p. 8
2022	Equus Parray et al.
2025	Equus Eshelman et al. p. 144

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No classification data are available

No information on subtaxa.

Diagnosis

No diagnoses are available