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Calippus proplacidus

Mammalia - Perissodactyla - Equidae

Taxonomy
Protohippus proplacidus was named by Osborn (1918). Its type specimen is AMNH 9115b, a partial skeleton (Upper and lower jaws of a young individual with milk dentition, mr, preformed, and a few fragments of the skeleton), and it is a 3D body fossil.

It was recombined as Merychippus (Protohippus) proplacidus by Stirton (1940); it was recombined as Merychippus proplacidus by Galbreath (1953); it was recombined as Calippus (Calippus) proplacidus by Hulbert (1988); it was considered a nomen dubium by Macdonald (1992); it was recombined as Calippus proplacidus by MacFadden (1998).

Synonyms
Synonymy list
YearName and author
1918Protohippus proplacidus Osborn p. 139 figs. Plates 25.7, 34.3. Text Fig. 112
1924Merychippus francisi Hay p. 9
1940Merychippus (Merychippus) francisi Stirton p. 181
1940Merychippus (Protohippus) proplacidus Stirton p. 182
1953Merychippus proplacidus Galbreath
1955Calippus francisi Quinn p. 27 figs. Pl. 4, Figs. 6 - 7
1969Calippus francisi Webb
1975Calippus francisi Forsten
1988Calippus (Calippus) proplacidus Hulbert, Jr. p. 235 figs. 5, 6A-6B
1998Calippus proplacidus MacFadden p. 550

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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
genusCalippus()
speciesproplacidus()

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 (Matthew, 1913) from the type and paratypes. (1) Protocone united with protoconule near summit of crown but not strongly united until near the base of the crown; (2) protocone of flattened oval shape; (3) fossette borders simple, fossettes contracted, prefossettes closed early in wear; (4) pli caballin rudimentary; (5) metastylid not separated from metaconid on J>2; (6) metaconid-metastylid pillars forming a column narrow at top, broader to'Vard base, separated by a shallow groove, deepening toward base but disappearing before it reaches the base; (7) heel of rna small, simple, (8) anterior cingulum prominent on inside and outside of tooth, extending to top of crown as in Hipparion. (9) Malar fossa apparently absent; (10) metatarsals long, slender, lateral digits much reduced; (11) ungual phalanges rather narrow.
J. H. Quinn 1955 (Calippus francisi)Smaller than C. placidus; upper teeth slightly curved and strongly hypsodont but shorter than later species and expanded antero-posteriorly at sum- mit of crowns; enamel pattern more com- plex than in later species; protocones of molars grooved at summit of crown; hypo- stylar fossette present; hypoconal groove open about half-way down the crown on the premolars and lower on molars; lower teeth with prominent parastylid; pli hypo- conids present; trace of pli caballinid on P. 2 only; hypoconulid of M. 3 with a deep internal groove.
R. C. Hulbert 1988Small equid with toothrow lengths of about 95 to 102 mm and unworn molar crown heights about 40 mm. Larger than C. regulus or C. elachistus, and with better developed styles and fossette plications. Less hypsodont, shallower linguaflexids, and less elongated metaconids and metastylids than C. placidus.