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Mesohippus exoletus

Mammalia - Perissodactyla - Equidae

Taxonomy
Anchitherium exoletum was named by Cope (1874).

It was synonymized subjectively with Mesohippus bairdi by Osborn and Wortman (1895), Matthew (1899) and Trouessart (1905); it was recombined as Miohippus exoletum by Hay (1902); it was considered a nomen dubium by Osborn (1904), Osborn (1918) and Macdonald (1992); it was recombined as Mesohippus exoletus by Stirton (1940), Scott (1941), Prothero and Shubin (1989) and MacFadden (1998).

Synonyms
Synonymy list
YearName and author
1874Anchitherium exoletum Cope
1902Miohippus exoletum Hay
1918Mesohippus trigonostylus Osborn p. 47 figs. Plate 2.5,6. Text Fig. 27.
1935Pediohippus trigonostylus Schlaikjer p. 144
1940Mesohippus exoletus Stirton p. 170
1940Mesohippus tribonostylus Stirton p. 170
1941Mesohippus exoletus Scott
1941Pediohippus trigonostylus Scott
1951Mesohippus trigonostylus Macdonald
1989Mesohippus exoletus Prothero and Shubin
1998Mesohippus exoletus MacFadden p. 543

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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()
genusMesohippus
speciesexoletus(Cope 1874)

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 (Mesohippus trigonostylus)The specific name M. trigonostylus refers to the progressive triallgular form of the plications of the hypo- style, which is highly distinctive. From the rudiment of the hypostyle on the post-cingulum, as seen in the M. bairdii stage, a cruciform plication extends anteriorly toward the metaloph, branching into an external pli hypostyle and an internal spur (see paratype, dp4, Plate 2.5) which connects with the metaloph. This condition of the hypostyle is very different from that in any other Middle Oligocene species (compare Plate 2.1-8). A somewhat similar condition of the hypostyle is seen in the type of Miohippus validus from the Protoceras zone.