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Calippus placidus

Mammalia - Perissodactyla - Equidae

Taxonomy
Protohippus placidus was named by Leidy (1869) [also, but incorrectly said to be 1858]. Its type specimen is USNM 621, a tooth (A left upper premolar, P2), and it is a 3D body fossil.

It was recombined as Merychippus placidus by Hay (1902) and Trouessart (1905); it was recombined as Protohippus (Calippus) placidus by Matthew and Stirton (1930); it was recombined as Calippus (Calippus) placidus by Hulbert (1988) and Prado and Alberdi (1996); it was considered a nomen dubium by Macdonald (1992); it was recombined as Calippus placidus by Stirton (1935), Johnston (1937), Stirton (1940), Quinn (1955), Dalquest and Hughes (1966), Webb (1969), Voorhies (1990) and MacFadden (1998).

Synonyms
Synonymy list
YearName and author
1869Protohippus placidus Leidy
1893Protohippus placidus Cope p. 26
1902Merychippus placidus Hay
1905Merychippus placidus Trouessart
1907Protohippus placidus Gidley p. 887
1918Protohippus placidus Osborn p. 133 figs. Plate 34.4. Text Figs. 106, 107, 116a
1930Protohippus (Calippus) placidus Matthew and Stirton p. 354
1935Calippus placidus Stirton
1937Calippus placidus Johnston
1940Calippus placidus Stirton p. 188
1955Calippus optimus Quinn p. 35
1955Calippus placidus Quinn p. 39
1966Calippus placidus Dalquest and Hughes
1969Calippus placidus Webb
1975Pseudhipparion optimum Forsten
1988Calippus (Calippus) placidus Hulbert, Jr. p. 234 fig. 9
1990Calippus placidus Voorhies
1996Calippus (Calippus) placidus Prado and Alberdi p. 676
1998Calippus placidus 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()
speciesplacidus(Leidy 1869)

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 (Leidy, 1869) (1) Separated from P. perditus as an animal of small stze. (2) Enamel plications in the type and some of the paratypes relatively simple; (3) crowns less curved than in P. perditus; (4) central lakes [fossettes] wide and gaping.
Neotype characters.- (Gidley, 1906, 1907) Based on fragment of skull, Amer. Mus. 10830. (1) Protocones directed well backward, as in P. perditus; (2) enamel borders of fossettes relatively simple; (3) upper molariform teeth of smaller size than in P. perditua, i. e. diameters of crown; (4) of greater comparative length than P. perditus; (5) of less curvature than P. perditua; (6) fossettes in true molars of less transverse width. (7) A slight depression in the malar bone immediately in front of the orbit, otherwise the facial region full and smooth as in P. perditus, (8) the lachrymal fossa shallow
and not sharply defined.
J. H. Quinn 1955 (Calippus optimus)Size intermediate to C. anatinus and C. placidus; styles of upper teeth delicate; ribs moderately prominent; fossettes angular with some bifid and tri- fid plications; protocone shorter and hy- poconal groove more open than in C. anatinus and C. placidus; lower molars with reduced and deflected metastylids; me- dian valley of molars deep; parastylid present; pli cahallinid absent; milk teeth high crowned, heavily cemented; parastylid present; hypostylid, protostylid and pli caballinid absent.
J. H. Quinn 1955Largest of the species of Caliprpus; protocone longer and plications heavier than in the other species; upper teeth less tapered than in C. optimus; upper milk teeth wider transversely.
R. C. Hulbert 1988Small equid with toothrow lengths of about 95 to 105 mm; unworn molar crown heights about 51 mm. DPOF long, oval and relatively deep (for a Calippus). Higher-crowned teeth than C. proplacidus. Larger than C. regulus and C. elachistus, with more complex fossettes, deeper linguaflexids, and a larger, moderate-sized DPl.