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Calippus circulus

Mammalia - Perissodactyla - Equidae

Taxonomy
Pliohippus circulus was named by Quinn (1955). Its type specimen is BEG 31191-10, a set of teeth (wer right cheek tooth series with p4-m3), and it is a 3D body fossil. Its type locality is Sam Houston, which is in a Barstovian terrestrial horizon in the Fleming Formation of Texas.

It was recombined as Merychippus circulus by Forsten (1975); it was recombined as Calippus (Grammohippus) circulus by Hulbert (1988); it was recombined as Calippus circulus by MacFadden (1998) and Kelly (1998).

Synonymy list
YearName and author
1955Pliohippus circulus Quinn p. 22 figs. Pl. 3, Figs. 5 - 8
1975Merychippus circulus Forsten p. 32 figs. Tables 13, 31; Figs. 4, SA, 5B
1988Calippus (Grammohippus) circulus Hulbert, Jr. p. 256 fig. 14
1998Calippus circulus Kelly
1998Calippus circulus MacFadden p. 550

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RankNameAuthor
kingdomAnimalia()
—Bilateria
—EubilateriaAx 1987
—Deuterostomia
phylumChordataHaeckel 1874
subphylumVertebrata
superclassGnathostomata
—Osteichthyes()
subclassSarcopterygii()
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
—Tetrapoda
—Reptiliomorpha
—Anthracosauria
subclassAmphibiosauriaKuhn 1967
—Cotylosauria()
—Amniota
subclassSynapsida
—Therapsida()
infraorderCynodontia()
—Mammaliamorpha
—Mammaliaformes
classMammalia
RankNameAuthor
—Theriamorpha(Rowe 1993)
—Theriiformes()
—Trechnotheria
—Cladotheria
—Zatheria
subclassTribosphenida()
subclassTheria
—Eutheria()
—Placentalia
—Boreoeutheria
—Laurasiatheria
—Scrotifera
—Euungulata
—Panperissodactyla
superorderPerissodactylamorpha
orderPerissodactyla()
superfamilyEquoidea
familyEquidae
subfamilyEquinae
tribeEquini
genusCalippus()
speciescirculus()

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.

†Calippus circulus Quinn 1955
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Diagnosis
ReferenceDiagnosis
J. H. Quinn 1955Size smaller than Pliohip- pus supremus; teeth shorter crowned· metaconid and metastylid closely a;- pressed and symmetrically rounded; meta- conid larger than metastylid; flexids short; parastylid sloping across anterior face of teeth and for most part reduced to a scar; protoconid and hypoconid deep and strongly rounded on premolars, less so on molars; hypoconulid prominent on premolars and with a hypostylid fold; hypoconulid narrow, not pronounced, and without a hypostylid fold on the molars.
A. -M. Forsten 1975Quinn (1955, pp. 23, 54, revised): Hypsodont. Teeth moderately curved; protocone elongate, slightly heeled and grooved in early wear; disconnected at summit of crown, but with long spur. Plication frequency moderate. Lower teeth with protoconid and hypoconid slightly flattened in early, rounded in late!" wear; metaconid and metastylid wide, flaring in early, rounded in late wear. Incipient pli caballinid; parastylid variable.
R. C. Hulbert 1988Cheekteeth with least unworn crown height of known species of the subgenus; unworn molar MSCH about 40 mm. Smaller than C. mmtini, with less complex fossettes, poorly developed pli caballins on premolars, and variable, often strong protostylids.