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Equus (Dolichohippus) simplicidens

Mammalia - Perissodactyla - Equidae

Taxonomy
Equus simplicidens was named by Cope (1892). Its type specimen is TMM 40282-6, a tooth (left M1), and it is a 3D body fossil.

It was recombined as Pliohippus simplicidens by Gidley (1901), Hay (1902), Gidley (1903), Trouessart (1905), Gidley (1907), Matthew (1909), Merriam (1916), Osborn (1918) and Schultz (1936); it was recombined as Plesippus simplicidens by Matthew (1924), Gidley (1930), Gazin (1936), Schultz (1936), Hibbard (1944), Strain (1966) and Repenning et al. (1995); it was recombined as Hippotigris simplicidens by McGrew (1944), Meade (1945) and Quinn (1955); it was recombined as Equus (Plesippus) simplicidens by Howe (1970) and Forsten and Eisenmann (1995); it was considered a nomen dubium by Macdonald (1992); it was recombined as Equus (Dolichohippus) simplicidens by Skinner (1972) and MacFadden (1998).

Synonyms
Synonymy list
YearName and author
1865Equus occidentalis Leidy
1869Equus tau Owen p. 565
1870Equus tau Owen
1892Equus simplicidens Cope p. 124 fig. 1
1893Equus simplicidens Cope p. 66
1893Equus cumminsii Cope p. 67
1901Equus occidentalis Gidley p. 114 fig. 10
1901Equus tau Gidley p. 120
1901Pliohippus simplicidens Gidley p. 124 fig. 13
1901Protohippus cumminsii Gidley p. 126 fig. 17
1902Merychippus cumminsii Hay
1902Pliohippus simplicidens Hay
1903Pliohippus simplicidens Gidley
1903Protohippus cumminsii Gidley
1905Merychippus cumminsii Trouessart
1905Pliohippus simplicidens Trouessart
1907Protohippus cumminsii Gidley
1907Pliohippus simplicidens Gidley p. 911
1909Pliohippus simplicidens Matthew
1909Protohippus cumminsii Matthew
1913Equus littoralis Hay p. 575
1916Pliohippus simplicidens Merriam
1917Pliohippus cumminsii Merriam
1918Pliohippus simplicidens Osborn p. 167 figs. Plates 24.5, 28.5. Text Fig. 134.
1918Pliohippus cumminsii Osborn p. 168 figs. Plate 24.3,4. Text Fig. 135
1921Pliohippus cumminsii Frick
1924Plesippus simplicidens Matthew
1930Plesippus simplicidens Gidley
1930Plesippus shoshonensis Gidley p. 301 fig. 1
1930Pliohippus cumminsii Hay
1930Equus achates Hay and Cook
1930Plesippus cumminsii Matthew and Stirton
1935Equus tau Schultz and Howard p. 286
1936Plesippus cumminsii Gazin
1936Plesippus simplicidens Gazin
1936Plesippus cumminsii Schultz
1936Plesippus simplicidens Schultz
1936Pliohippus simplicidens Schultz
1940Equus cumminsi Stirton p. 192
1940Equus shoshonensis Stirton p. 195
1940Equus simplicidens Stirton p. 195
1942Plesippus shoshonensis Gazin
1944Plesippus cumminsii Hibbard
1944Plesippus simplicidens Hibbard
1944Hippotigris simplicidens McGrew p. 55
1945Hippotigris simplicidens Meade
1949Equus simplicidens Hibbard and Riggs
1950Amerhippus occidentalis Hoffstetter
1951Equus simplicidens Hibbard
1952Equus occidentalis Hoffstetter
1955Hippotigris shoshonensis Quinn p. 46
1955Hippotigris simplicidens Quinn p. 46
1955Asinus cumminsii Quinn p. 52
1957Onager littoralis Quinn p. 13
1958Asinus pons Quinn p. 605 figs. 1, 2
1966Equus pons Azzaroli
1966Equus cumminsii Strain
1966Plesippus simplicidens Strain
1970Equus (Plesippus) simplicidens Howe p. 959
1972Equus (Dolichohippus) simplicidens Skinner p. 118
1979Equus (Hemionus) tau Dalquest p. 242
1980Equus simplicidens Kurten and Anderson p. 285
1980Equus cumminsii Kurten and Anderson p. 287
1980Equus tau Kurten and Anderson p. 288
1980Equus occidentalis Kurten and Anderson p. 289
1989Equus simplicidens Winans
1989Plesippus shoshonensis Winans p. 301 fig. 1
1990Equus simplicidens Schultz
1995Equus (Plesippus) simplicidens Forsten and Eisenmann p. 88
1995Equus cumminsii Kelly p. 14
1995Equus simplicidens Kelly p. 19
1995Plesippus shoshonensis Repenning et al.
1995Plesippus simplicidens Repenning et al.
1997Equus simplicidens Kelly
1998Equus cumminsii Kelly
1998Equus simplicidens Kelly
1998Equus (Dolichohippus) simplicidens MacFadden p. 551

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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()
infraorderCynodontia()
RankNameAuthor
Epicynodontia
infraorderEucynodontia
Probainognathia
Mammaliamorpha
Mammaliaformes
classMammalia
subclassTribosphenida()
infraclassEutheria()
Placentalia
orderPerissodactyla()
suborderLophodontomorpha
infraorderEuperissodactyla
Hippomorpha
superfamilyEquoidea
familyEquidae
subfamilyEquinaeSteinmann and Döderlein 1890
tribeEquini
genusEquus
subgenusDolichohippus(Heller 1912)
speciessimplicidens()

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 (Pliohippus cumminsii)(Cope, 1893, p. 67) (1) Of smaller size than the type of Pliohippus simplicidens. (2) Enamel borders
of fossettes entirely simple [due to extreme wear]; (3) prominent convexity of the internal wall of the paracone and metacone, from which it results that the external enamel border of each fossette is deeply concave [convex]; (4) proto- cone with a short anteroposterior diameter as in P. simplicidens, not bilobate or grooved on the internal face; (5) an angle of the posterior border of the prefossette represents the loop [crochet fold]; (6) cylindric character of paracone and metacone.
H. F. Osborn 1918(1) about that of E. cahallus. (2) Internal column [protocone] is of moderate anteroposterior extent, its posterior border marking the anterior third of the posterior lake [post fossette]; (3) its long diameter is considerably less than half that of the crown; (4) extreme simplicity of the enamel borders of the lakes; (5) pli caballin, also a crochet fold in prefossette; (6) metastyle narrowed and not flattened; (7) parastyle more flattened.
J. W. Gidley 1930 (Plesippus shoshonensis)Size about that of Equus niobrarensis or of a domestic horse of about fourteen or fifteen hands height; skull with shallow but well defined facial pits; muzzle and facial region long with orbit set well back; nasals relatively long and slender; basicranial region shorter and more bent downward than in Equus; cheek teeth long as in Equus, but in general more curved than is usual in the latter, and less curved than in Pliohippus; cement lakes in upper cheek teeth somewhat more open and with less elaborate enamel folding than is usual in Equus; proto- cones much more lengthened anteroposteriorly than in Pliohippus but less so than the average in Equus; lingual wall of protocone completely flattened, in some specimens definitely bent inward and presenting the longitudinal groove so com- monly found in Equus.
This species may be distinguished from P. simplicidens by the seemingly more distinct invagination of the facial pits; the more posterior position of the orbits; and from both P. simplicidens and P. proversus,by the generally more advanced or Equus-like development of the cheek teeth as indicated by the greater length- ening and greater curvature of the upper molars and by the generally more trans- versely flattened and grooved protocones.
J. H. Quinn 1957 (Onager littoralis)Smallest of the Equini, teeth slightly larger than those of Nannippus phlegon. (From Hay, 1913a, p. 575) "Characterized by teeth of small size . . . enamel surrounding the lakes rather strongely folded. The crown somewhat more curved than in E. leidyi."
J. H. Quinn 1958 (Asinus pons)Teeth slightly larger than in Asinus somaliensis Noak, protocones shorter with pronounced spur on anterior border as in A. mexicanus (Lance), more hypsodont than in A. mexicanus; metarsal equal in length to that of A. somaliensis, larger and stouter than in A. mexicanus; metacarpal longer than in A. somaliensis.
M. C. Winans 1989 (Plesippus shoshonensis)Size about that of Equus niobrarensis or of a domestic horse of about fourteen or fifteen hands height; skull with shallow but well defined facial pits; muzzle and facial region long with orbit set well back; nasals relatively long and slender; basicranial region shorter and more bent downward than in Equus; cheek teeth long as in Equus, but in general more curved than is usual in the latter, and less curved than in Pliohippus; cement lakes in upper cheek teeth somewhat more open and with less elaborate enamel folding than is usual in Equus; proto- cones much more lengthened anteroposteriorly than in Pliohippus but less so than the average in Equus; lingual wall of protocone completely flattened, in some specimens definitely bent inward and presenting the longitudinal groove so com- monly found in Equus.
This species may be distinguished from P. simplicidens by the seemingly more distinct invagination of the facial pits; the more posterior position of the orbits; and from both P. simplicidens and P. proversus,by the generally more advanced or Equus-like development of the cheek teeth as indicated by the greater length- ening and greater curvature of the upper molars and by the generally more trans- versely flattened and grooved protocones.