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Miohippus equiceps

Mammalia - Perissodactyla - Equidae

Taxonomy
Anchitherium equiceps was named by Cope (1878). Its type specimen is AMNH 7261, a partial skeleton (a portion of the skeleton including a com- plete cranium of one individual ), and it is a 3D body fossil.

It was recombined as Mesohippus equiceps by Farr (1896), Matthew (1899) and Osborn (1904); it was recombined as Miohippus equiceps by Cope (1894), Roger (1896), Hay (1902), Osborn (1918), Hay (1930), Stirton (1940), Macdonald (1963), Macdonald (1970), Fremd (1994) and Strganac (2011).

Synonyms
Synonymy list
YearName and author
1878Anchitherium equiceps Cope p. 73
1879Anchitherium brachylophus Cope
1894Miohippus brachylophus Cope p. 791
1894Miohippus equiceps Cope p. 791
1895Miohippus brachylophus Scott
1896Mesohippus equiceps Farr
1896Miohippus brachylophus Roger
1896Miohippus equiceps Roger
1898Miohippus brachylophus Trouessart
1899Mesohippus brachylophus Matthew
1899Mesohippus equiceps Matthew
1902Miohippus brachylophus Hay p. 613
1902Miohippus equiceps Hay p. 614
1904Mesohippus brachylophus Osborn p. 168
1904Mesohippus equiceps Osborn p. 168
1905Mesohippus acutidens Sinclair p. 141 figs. Pl. 18
1907Mesohippus acutidens Merriam and Sinclair
1907Mesohippus brachylophus Merriam and Sinclair
1909Mesohippus brachylophus Matthew
1918Miohippus equiceps Osborn p. 59 figs. Plates 3.10, 5.4,5, 6.1. Text Fig. 37
1918Miohippus brachylophus Osborn p. 60 figs. Plates 3.9, 5.3. Text Fig. 38.
1918Miohippus acutidens Osborn p. 64 figs. Plate 4.7. Text Fig. 44
1930Miohippus brachylophus Hay
1930Miohippus equiceps Hay
1940Miohippus acutidens Stirton p. 172
1940Miohippus brachylophus Stirton p. 172
1940Miohippus equiceps Stirton p. 172
1963Miohippus equiceps Macdonald
1970Miohippus equiceps Macdonald
1994Miohippus equiceps Fremd
2011Miohippus equiceps Strganac p. 22

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RankNameAuthor
kingdomAnimalia()
Bilateria
EubilateriaAx 1987
Deuterostomia
phylumChordataHaeckel 1874
subphylumVertebrata
superclassGnathostomata
Osteichthyes()
subclassSarcopterygii()
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
Tetrapoda
Reptiliomorpha
Anthracosauria
subclassAmphibiosauriaKuhn 1967
Cotylosauria()
Amniota
subclassSynapsida
Therapsida()
infraorderCynodontia()
Mammaliamorpha
Mammaliaformes
RankNameAuthor
classMammalia
Theriamorpha(Rowe 1993)
Theriiformes()
Trechnotheria
Cladotheria
Zatheria
subclassTribosphenida()
subclassTheria
Eutheria()
Placentalia
Boreoeutheria
Laurasiatheria
Scrotifera
Euungulata
Panperissodactyla
superorderPerissodactylamorpha
orderPerissodactyla()
superfamilyEquoidea
familyEquidae
subfamilyAnchitheriinae()
genusMiohippus
speciesequiceps()

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.

Miohippus equiceps Cope 1878
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Invalid names: Anchitherium brachylophus Cope 1879 [synonym], Mesohippus acutidens Sinclair 1905 [synonym]
Diagnosis
ReferenceDiagnosis
E. D. Cope 1878The skull is considerably larger than that of A. bairdi, and the lengthis greater as compared to the transverse and vertical diameters. The pre- orbital region is but little concave, and the anterior border of the orbit is above the posterior half of the first true molar. The molar teeth present a tubercle between the anterior lobes, and a weak cingulum extends round the inner base of the anterior one, and in the second premolar, round the base of both inner lobes. Thence it passes round the anterior base of the crown and ceases in a tubercle which rises in contact with the anterior median crest. On the posterior side of the crown the cingulum in like manner terminates in the large three-sided posterior marginal tubercle. The anterior median tubercle-crest is well distinguished from the anterior inner tubercle and is directed very obliquely. The posterior median crest is continuous with the inner, and is well separated from the external crests. The external basal cingulum is robust, the columns are prominent, and the outer faces of the external crescents deeply impressed but with a well marked median ridge. The external cingulum and its margins is ru- gose; other parts of the enamel smooth. The first premolar has two roots; the second premolar is as long as the fourth, and longer than the last true molar.
W. J. Sinclair 1905 (Mesohippus acutidens)
Superior canines long and pointed, with acute anterior and posterior edges. lVletaloph hardly interrupted by metaconule, sharply separated by a deep notch from the ectoloph. Protoloph with well marked protoconule, united with ectoloph by a narrow shape-edged ridge which ,videns in moderately worn teeth. Parastyle broadly rounded except in lYP where it is compressed antero-posteriorly. lYP with metaloph storter than protoloph
(i.e., as 8.5 mm. : 12..3 mm.), producing al.most a triangular out- line for the tooth crown. Mesostyle sharply defined and ribs broadly rounded and prominent. The measurements seem also to be characteristic.
H. F. Osborn 1918 (Miohippus brachylophus)(Cope, 1878) ''The median and inner tubercles are not deeply separated, and the former are cut off
from the external crescents by a deep fissure. There is no tubercle between the bases of the inner cones, nor is there any internal cingulum. The anterior cingulum does not develop a distinct tubercle, and does not extend to the anterior extremity of the anterior outer crescent. The posterior cingulum develops a large trihedral tubercle, and then extends nearly to the external crescent. The external cingulum is robust, and the external columns are prominent; the interven- ing spaces are impressed, and have a distinct median ridge. Enamel smooth or slightly regose at base of crown."
(Matthew, 1913) (1) No cingulum around protocone; (2) no basal cusp in medivallum; (3) no distinct cusp on the anterior cingulum; (4) parastyle on p2 less prominent than type of M. equiceps. This species is regarded by Matthew as rather close toM. equiceps. An animal of the same size and from the same general level as M. equiceps is represented by a fine skull, Amer. Mus. 7262, which is provisionally referred to this species. Provisionally referred specimens are also palates with teeth, Amer. Mus. 7282, 7292, and the upper jaw, Amer. Mus. 7266.
H. F. Osborn 1918(Cope, 1878, pp. 73, 74} (1) Preorbital region but little concave; (2) anterior border of orbit above posterior half of first true molar. (3) Molars with a tubercle between the anterior lobes; (4) a weak cingulum around inner base of protoloph; (5) p2 with cingulum around protoloph and metaloph; (6) a large three-sided hyp.ostyle; (7) external basal cingulum robust; (8) para- and metacones with median ridges well mark-ed. (9) I t differs from the type of Miohippus (A.) condoni in the presence of median internal tubercle and cingulum, and (10) also in the presence of a trihedral instead of a linear hypostyle..
H. F. Osborn 1918 (Miohippus acutidens)(Sinclair, 1905, p. 141) "Superior canines and pointed, with acute anterior and posterior edges.
Metaloph hardly interrupted by metaconule, sharply separated by a deep notch from the ectoloph. Protoloph with well marked protoconule, united with ectoloph by a narrow sha[r]pe-edged ridge which widens in moderately worn teeth. Parastyle broadly rounded except in M3 where it is compressed antero-posteriorly. M3with metaloph s[h]orter than pro- toloph (i. e., as 8.5 mm.: 12.3 mm.), producing almost a triangular outline for the tooth crown. Mesostyle sharply defined and ribs broadly rounded and prominent. The measurements seem also to be characteristic."
Additi011al characters.- (Osborn, 1918) (1) Canines probably male; (2) a large hypostyle on p1-m3; (3) m3giving off a narrow spur-like cingulum which borders the hypocone posteriorly; (4) one or more small tubercles at entrance of medi- vallum, no other traces of internal cingulum; (5) external cingulum not continued across the bases of the styles; (6) orbit
almost completely closed by a strongly developed postorbital process; (7) a well marked preorbital fossa; (8) differs from M. brachystylus of the Leptauchenia zone in the form of the postorbital process and in the closure of the supraorbital notch.
Measurements
No measurements are available
Composition: phosphaticsubp
Environment: terrestrialsubc
Locomotion: actively mobilec
Life habit: ground dwellingf
Diet: browserf
Reproduction: viviparoussubc
Created: 2005-06-08 10:11:09
Modified: 2005-08-31 16:55:50
Source: f = family, subc = subclass, c = class, subp = subphylum
References: Ji et al. 2002, Hendy et al. 2009, Carroll 1988, Lillegraven 1979, Nowak 1991

Age range: base of the Whitneyan to the top of the Monroecreekian or 33.30000 to 24.80000 Ma

Collections (12 total)


Time interval Ma Country or state Original ID and collection number
Whitneyan33.3 - 30.8Canada (Saskatchewan) Miohippus equiceps (17372)
Geringian30.8 - 26.3USA (South Dakota) Miohippus equiceps (17623 17626 17627 17634 17635 17636 17638 17641)
Arikareean30.8 - 20.43USA (Montana) Miohippus equiceps (17509)
Arikareean30.8 - 20.43USA (Oregon) Anchitherium equiceps (180202)
Monroecreekian26.3 - 24.8USA (Washington) Miohippus equiceps (119838)