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Merychippus calamarius

Mammalia - Perissodactyla - Equidae

Taxonomy
Hippotherium calamarium was named by Cope (1875). Its type specimen is USNM 2572, a partial skull (This three-toed horse is indicated by the oral and palatine parts of the skull with the superior dental series of both sides, together with one mandibular ramus), and it is a 3D body fossil.

It was recombined as Hipparion calamarius by Roger (1896), Trouessart (1898), Matthew (1899) and Hay (1902); it was recombined as Neohipparion calamarius by Matthew (1904) and Trouessart (1905); it was recombined as Merychippus (Merychippus) calamarius by Stirton (1940); it was recombined as Stylonus calamarius by Kelly and Lander (1988); it was recombined as Merychippus calamarius by Gidley (1907), Osborn (1918), Merriam (1919), Hay (1930), Kelly (1995) and MacFadden (1998).

Synonymy list
YearName and author
1875Hippotherium calamarium Cope p. 2–3
1889Hippotherium calamarium Cope p. 451
1896Hipparion calamarius Roger
1898Hipparion calamarius Trouessart
1899Hipparion calamarius Matthew
1902Hipparion calamarius Hay
1904Neohipparion calamarius Matthew
1905Neohipparion calamarius Trouessart
1907Merychippus calamarius Gidley
1918Merychippus calamarius Osborn p. 123 figs. Plates 11.4, 17.8, 18.2,6. Text Fig. 98
1919Merychippus calamarius Merriam
1930Merychippus calamarius Hay
1940Merychippus (Merychippus) calamarius Stirton p. 181
1988Stylonus calamarius Kelly and Lander
1995Merychippus calamarius Kelly
1998Merychippus calamarius MacFadden p. 547

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Nephrozoa
Deuterostomia
phylumChordataHaeckel 1847
subphylumVertebrata
superclassGnathostomata
Osteichthyes()
Sarcopterygii
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
Tetrapoda()
Reptiliomorpha
Anthracosauria
Batrachosauria()
Cotylosauria()
Amniota
Synapsida()
Therapsida()
RankNameAuthor
infraorderCynodontia()
Epicynodontia
infraorderEucynodontia
Probainognathia
Mammaliamorpha
Mammaliaformes
classMammalia
subclassTribosphenida()
infraclassEutheria()
Placentalia
orderPerissodactyla()
suborderLophodontomorpha
infraorderEuperissodactyla
Hippomorpha
superfamilyEquoidea
familyEquidae
subfamilyEquinaeSteinmann and Döderlein 1890
genusMerychippus
speciescalamarius()

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.

Diagnosis
ReferenceDiagnosis
H. F. Osborn 1918(Cope, 1875) (1) "The typical specimen belongs to an adult animal, and was taken from the matrix
by myself, without admixture of others." (2) Protocone column large, its centre anterior to the middle transverse line of the crown, an angular projection toward the protoconule, actually connecting with the protoconule in m2; (3) dentinal band connecting the inner crescents [pl ml], giving off two or rarely one fold [double pli caballin] in the crochet region; (4) borders of fossettes much plicate, anterior border of protoconule giving off from four to six folds; (4) posterior border of postfossette exhibits one deep fold, which is generally bifurcated [hypostyle region]; (5) p1 small, two-rooted; (6) no basal cingulum on either jaw; (7) molar, ms, smaller than the three preceding it.
(Matthew, 1913) (8) Grinding teeth extremely long-crowned; (9) protocone separate to about one-third from base,
suboval on premolars, more flattened on molars; (10) plications of enamel lake borders disappearing in well (two-thirds or more) worn teeth; (11) pli caballin fold double, disappearing about one-fourth from base; (12) metastylid not separate on P2· (13) Lachrymal fossa apparently large; (14) malar fossa variable, not very deep.