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Merychippus (Protohippus)

Mammalia - Perissodactyla - Equidae

Taxonomy

Equus (Protohippus) was named by Leidy (1858) [named as subgenus of Equus by Leidy 1858; raised to genus level; also recognized by Osborn 1918]. Its type is Equus (Protohippus) perditus.

It was synonymized subjectively with Merychippus by Hay (1902), McGrew and Meade (1938), Olson and McGrew (1941), Dorr (1956) and Shotwell (1961); it was Merychippus (Protohippus) by Stirton (1940); it was reranked as Protohippus by Leidy (1869), Leidy (1873), Cope (1881), Gidley (1907), Scott (1913), Quinn (1955), Hulbert (1988), Carroll (1988), Prothero and Schoch (1989), Kelly (1995), Prado and Alberdi (1996), MacFadden (1998), MacFadden and Dobie (1998), Hulbert and Whitmore (2006) and May (2019).

It was assigned to Equus by Leidy (1858); to Palaeotheriinae by Cope (1881); to Protohippinae by Gidley (1907); to Merychippus by Stirton (1940); to Protohippina by Hulbert (1988) and Prado and Alberdi (1996); to Equidae by Leidy (1869), Leidy (1873), Scott (1913), Carroll (1988) and MacFadden and Dobie (1998); to Protohippini by Quinn (1955), Kelly (1995) and Hulbert and Whitmore (2006); and to Equini by Prothero and Schoch (1989), MacFadden (1998) and May (2019).

Subtaxa

Merychippus (Protohippus) secundus

Synonyms

Eoequus was named by Quinn (1955).

It was synonymized subjectively with Merychippus by Forsten (1975); it was synonymized subjectively with Protohippus by Hulbert (1988) and MacFadden (1998).

It was assigned to Equini by Quinn (1955).
Protohippus medius was named by Cope (1892). It is a 3D body fossil. Its type locality is Sappa Creek, which is in a Barstovian terrestrial horizon in Kansas.

It was synonymized subjectively with Merychippus insignis by Hay (1902), Hay (1926) and Hay (1930); it was considered a nomen dubium by Korth (2000).

Synonymy list

Year	Name and author
1858	Equus (Protohippus) Leidy p. 26
1869	Protohippus Leidy p. 275
1873	Protohippus Leidy p. 322
1881	Protohippus Cope p. 399
1892	Protohippus medius Cope p. 944 fig. 5
1893	Protohippus medius Cope p. 25
1907	Protohippus Gidley p. 867
1907	Protohippus medius Merriam and Sinclair
1913	Protohippus Scott p. 290
1920	Protohippus medius Matthew
1940	Merychippus (Protohippus) Stirton p. 181
1955	Protohippus Quinn p. 13
1955	Eoequus Quinn p. 54
1988	Protohippus Carroll
1988	Protohippus Hulbert, Jr. p. 281
1989	Protohippus Prothero and Schoch p. 532
1995	Protohippus Kelly p. 25
1996	Protohippus Prado and Alberdi p. 676
1998	Protohippus MacFadden p. 549
1998	Protohippus MacFadden and Dobie
2006	Protohippus Hulbert and Whitmore p. 17
2019	Protohippus May p. 101 fig. 106

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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
—	Mammaliaformes

Rank	Name	Author
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
subfamily	Equinae
genus	Merychippus
subgenus	Protohippus	()

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.

Subg. †Merychippus (Protohippus) Leidy 1858

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†Merychippus (Protohippus) secundus Osborn 1918

Diagnosis

Reference	Diagnosis
R. C. Hulbert 1988	Medium- to large-sized, hypsodont, tridactyl equids with toothrow lengths generally between 125 and 145 mm in mature individuals. Malar fossa absent. DPOF large, teardrop-shaped, relatively shallow; distinctly rimmed dorsally and posteriorly in earlier populations, often with a small posterior pocket; less distinct in later populations, without a pocket. Lacrimal bone large, included in posterior region of DPOF. Diastema short; rostrum broad, but not to the degree of advanced species of Calippus; incisors form typical equine rounded arcade. Upper cheekteeth with large, elongate-oval protocones that are isolated from the protoselene to varying degrees during early wear-stages (most prevalent on P34 and M3); moderately large, single pli caballins on P34 (smaller and less persistent with wear on molars); simple but relatively persistent fossette plications; hypoconal groove generally remains open until at least middle wear; prominent parastyles on P34. Large protostylids on permanent and deciduous lower cheekteeth. Variably developed ectostylids on dp2-dp4.