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Miohippus obliquidens

Mammalia - Perissodactyla - Equidae

Taxonomy
Mesohippus obliquidens was named by Osborn (1904). Its type specimen is AMNH 668, a skull (skull and jaws), and it is a 3D body fossil. Its type locality is Middle Oreodon Beds (1892 AMNH Collection), which is in an Orellan terrestrial horizon in the Brule Formation of South Dakota.

It was synonymized subjectively with Mesohippus bairdi by Sinclair (1924); it was recombined as Miohippus obliquidens by Prothero and Shubin (1989) and MacFadden (1998).

Synonyms
Synonymy list
YearName and author
1904Mesohippus brachystylus Osborn
1904Mesohippus eulophus Osborn
1904Mesohippus obliquidens Osborn
1904Miohippus meteulophus Osborn
1904Mesohippus eulophus Osborn p. 173 fig. 5
1904Mesohippus obliquidens Osborn p. 173 figs. fig. 4, Pl. v, C
1904Mesohippus brachystylus Osborn p. 175 figs. fig. 6, Pl. v, E
1908Mesohippus brachystylus Douglass p. 270
1908Mesohippus brachystylus Lambe
1918Mesohippus obliquidens Osborn p. 48 figs. Plates 1.5, 2.7. Text Fig. 28
1918Mesohippus eulophus Osborn p. 49 figs. Plates 1.6, 2.8. Text Fig. 29
1918Miohippus meteulophus Osborn p. 51 figs. Plates 1.7, 3.1. Text Fig. 30
1918Miohippus brachystylus Osborn p. 53 figs. Plates 1.8, 3.2. Text Fig. 31
1920Mesohippus meteulophus Gregory
1930Mesohippus meteulophus Hay
1930Miohippus brachystylus Hay
1935Pediohippus antiquus Schlaikjer p. 141
1935Pediohippus brachystylus Schlaikjer p. 144
1940Mesohippus antiquus Stirton p. 170
1940Mesohippus eulophus Stirton p. 170
1940Mesohippus obliquidens Stirton p. 170
1940Miohippus brachystylus Stirton p. 172
1940Miohippus metulophus Stirton p. 172
1941Mesohippus meteulophus Scott
1941Pediohippus brachystylus Scott
1951Mesohippus meteulophus Macdonald
1974Miohippus antiquus Forsten
1989Miohippus obliquidens Prothero and Shubin
1998Miohippus obliquidens MacFadden p. 544

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Nephrozoa
Deuterostomia
phylumChordataHaeckel 1847
OlfactoresJefferies 1991
subphylumVertebrata
Gnathostomata()
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
subfamilyAnchitheriinae()
genusMiohippus
speciesobliquidens()

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 (Miohippus brachystylus) (Osborn, 1904, 1917) The name refers (1) to the broad rounded para8tyle, readily distinguishable from the flattened angulate parastyle of Mesohippua eulophus, Miohippus meteulophus, and Hypohippus. This species is further distinguished by: (2) p2-4 exceeding ml-3 in length (the reverse Occurs in M. eulophus); (3) broadly .depressed proto- and metalophs; (4) protoloph interrupted, with large oval protocone and distinct protoconule uniting externally with parastyle as in M. bairdii; (5) ectoloph with broad, prominent, rounded parastyle and well defined mesostyle, para- and metacone ribs defined; (6) hypostyle connected with cingulum but giving off a strong outward spur. (7) A vertically broad, shallow lachrymo-malar fossa (as compared with the narrow fossa in M. meteulophus); (8) facial exceeds cranial length.
H. F. Osborn 1918 (Mesohippus eulophus)(Osborn, 1904) "Distinguished from M. bairdi[i] by (1) deep preorbital [lachrymal] fossa, which is deeper also than in M. hypostylus; (2) large size of m3 ; (3) protoloph with very faint protoconule, and strongly connected with parastyle, constituting a nearly perfect anterior crest; metaloph also continuous; (4) as in M. meteulophus M1-M3 exceed in linear measurement p2-p4; (5) p4 slightly narrower than m1; (6) series of grinding teeth, mLp2, narrowing anteriorly."
H. F. Osborn 1918(Osborn, 1904) "Distinguished from the other species of the Oreodon Beds by (1) large size of skull and teeth as compared with M. bairdii, (2) preorbital Oachrymal] fossa shallow or wanting, (3) but especially by the high crowns of upper and lower molars: ectoloph of m1 measures .0105 vertical as compared with .008 in an unworn m1 crown of M. bairdi[i], (4) metaloph elevated, metaconule not being clearly defined, (5) proto- and metalophs directed obliquely back ward at a sharp angle with ectoloph, to which fact the name M. obliquidens refers." This is one of the horses of relatively larger size from the Upper Oreodon zone, possessing also relatively long-crowned molar grinding teeth.
H. F. Osborn 1918 (Miohippus meteulophus)(Osborn, 1904, p. 174) "This species is a successor of M. eulophus,from which it is distinguished (1)by its decidedly more elongate or hypsodont molar crowns, the crests being .002 higher; (2) by its larger size; (3) unlike M. eulophua p4 is broader than m1, a progressive stage towards the equine condition; (4) it accents theM. eulophua char- acter of the heavy but continuous meta- and protolophs which are not distinctly interrupted by conules. In the ectoloph the parastyle, mesostyle, and ribs are sharply-defined but not prominent, in fact, the ectoloph is somewhat flattened. (5) Another feature is that the protoloph is more elongate transversely than the metaloph, causing these crests to be somewhat asymmetrical as in M. latidens."

Additional characters,- (Osborn, 1918) (6) P2-4 of less length than m1- 3, i.e. Pms.