|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Mammalia - Perissodactyla - Equidae
It was recombined as Hipparion retrusum by Trouessart (1898) and Hay (1902); it was recombined as Neohipparion retrusum by Matthew (1909) and Merriam (1917); it was recombined as Protohippus retrusus by Osborn (1918) and Hay (1930); it was recombined as Nannippus retrusus by McGrew and Meade (1938), Stirton (1940) and Lance (1950); it was recombined as Griphippus retrusus by Quinn (1955); it was considered a nomen dubium by Macdonald (1992); it was recombined as Pseudhipparion retrusum by Ameghino (1904), Webb (1969), Webb and Hulbert (1986), Kelly and Lander (1988) and MacFadden (1998).
|Year||Name and author|
|1889||Hippotherium retrusum Cope p. 446|
|1898||Hipparion retrusum Trouessart|
|1902||Hipparion retrusum Hay p. 620|
|1904||Pseudhipparion retrusum Ameghino|
|1907||Hippotherium retrusum Gidley p. 906|
|1909||Neohipparion retrusum Matthew|
|1917||Neohipparion retrusum Merriam|
|1918||Protohippus retrusus Osborn p. 142 figs. Text Fig. 114|
|1930||Protohippus retrusus Hay|
|1938||Nannippus retrusus McGrew and Meade p. 201|
|1940||Nannippus retrusus Stirton p. 186|
|1950||Nannippus retrusus Lance|
|1955||Griphippus retrusus Quinn|
|1969||Pseudhipparion retrusum Webb|
|1986||Pseudhipparion retrusum Webb and Hulbert, Jr.|
|1988||Pseudhipparion retrusum Kelly and Lander|
|1998||Pseudhipparion retrusum MacFadden p. 548|
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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.
|H. F. Osborn 1918|| (Matthew, 1913, Osborn, 1918) (1) Molar size intermediate, somewhat larger than in P. placidus but
apparently with shorter crowns; (2) crowns strongly curved; (3) protocone separate from protoloph in m2, united in m1; (4) protocone and hypocone united by longitudinal isthmus; (5) protocone flattened oval, posterior in position; (6) pli caballin fold present on little worn teeth, absent on half worn teeth; (7) two folds and minor accessory folds on each side of metaloph projecting into pre- and postfossettes; (8) a single inferior fold (crochet) in prefossette; (9) parastyle narrow, mesostyle broad at base and narrowing rather slightly toward crown.
(Matthew, 1913) "These two type teeth cannot go together as placed; they may not belong to the same animal; the right hand tooth (A) might be Merychippus; the left hand tooth, if normal, does not agree well with any of the genera. If normal it represents an undescribed genus on the criteria used to separate the Miocene and Pliocene genera. If placed in Protohippus it should be in quotes."