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Diplacodon emarginatus

Mammalia - Perissodactyla - Brontotheriidae

Taxonomy
Diplacodon emarginatus was named by Hatcher (1895) ["emarginatus": assigned tentatively, with Protitanotherium suggested if a new genus name is called for]. Its type specimen is PU 11242, a skull, and it is a 3D body fossil. Its type locality is Kennedy's Hole, which is in an Uintan terrestrial horizon in the Uinta Formation of Utah.

It was recombined as Protitanotherium emarginatum by Peterson (1913), Osborn (1923), Osborn (1929), Peterson (1934), Mader (1989), Mader (2000), Mihlbachler (2008) and Mader (2008).

Synonyms
Synonymy list
YearName and author
1895Diplacodon emarginatus Hatcher p. 1084 figs. Plates XXXVIII - XXXIX
1902Diplacodon emarginatus Hay
1908Protitanotherium superbum Osborn
1913Protitanotherium emarginatum Peterson p. 31
1923Protitanotherium emarginatum Osborn p. 3
1923Protitanotherium superbum Osborn p. 3
1929Protitanotherium emarginatum Osborn p. 377 figs. Plates LXVni, LXIX; text figures 24, 29, 87, 112, 314-320, 374, 375, 408, 648, 649, 712
1934Protitanotherium emarginatum Peterson
1977Sthenodectes australis Wilson
1989Protitanotherium emarginatum Mader
2000Protitanotherium emarginatum Mader
2008Protitanotherium emarginatum Mader p. 8
2008Protitanotherium emarginatum Mihlbachler p. 157

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RankNameAuthor
kingdomAnimalia()
Triploblastica
Nephrozoa
Deuterostomia
phylumChordataHaeckel 1847
OlfactoresJefferies 1991
subphylumVertebrata
Gnathostomata()
Osteichthyes()
Sarcopterygii
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
Tetrapoda()
Reptiliomorpha
Anthracosauria
Batrachosauria()
Cotylosauria()
Amniota
Synapsida()
RankNameAuthor
Therapsida()
infraorderCynodontia()
Epicynodontia
infraorderEucynodontia
Probainognathia
Mammaliamorpha
Mammaliaformes
classMammalia
subclassTribosphenida()
infraclassEutheria()
Placentalia
orderPerissodactyla()
familyBrontotheriidae()
subfamilyBrontotheriinaeMarsh 1873
tribeBrontotheriiniMarsh 1873
subtribeBrontotheriinaMarsh 1873
genusDiplacodon
speciesemarginatus

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
Osborn 1929Pi-ms 294 millimeters (esti- mated),piwithasmalltalonid;ii small,round-topped; is large, bluntly pointed ; ia much larger than is. Lower canine more erect, recui'ved, and abruptly swelling at the base. Postcanine diastema short (27 mm.) but relatively longer than in P. superbum. Lower pre- molars and molars more brachyodont, with sloping curves.
M. C. Mihlbachler 2008Protitanotherium emarginatum is a large brontothere with small, elliptical frontonasal horns positioned low on the skull. The nasal incision is dorsoventrally shallow and extends as far back as the P4. The nasal process is nearly horizontal, unelevated, short and broad, with thickened sides, and with a thickened and imperfectly rounded distal edge with a distinct median notch. The lateral margins of the nasal process are not upturned. The orbits are positioned above M2. The premaxillomaxil- lary rostrum thickens posteriorly and it is not sealed by bone dorsally. Other cranial characteristics include a saddle-shaped crani- um, separate parasagittal ridges that strongly constrict the dorsal surface of the cranium posteriorly, nearly straight zygomatic arches, and tube-shaped and mediolaterally angled external auditory pseudomeati. The posterior narial canal does not extend past the foramen ovale and large ventral sphenoidal fossae are absent.
Dentally, Protitanotherium emarginatum has three intermediate-sized subglobular up- per incisors, and metacones on P1 and P2. Premolar hypocones are absent, although a short lingual crest can occasionally be seen extending from the protocones. The molars have tall lingually angled ectolophs with weak labial ribs, and thinned lingual ectoloph enamel with wedge-shaped paracones and metacones. A cingular parastyle shelf is absent. Central molar fossae are present, but anterolingual cingular cusps are absent. Paraconules and metalophs are absent. The lower dentition includes three intermediate- sized semispatulate incisors with an enlarged i2, a distinct postcanine diastema, a metaco- nid on p4 but not on p2 or p3, shallow molar basins, and a slender m3.
Protitanotherium emarginatum most close- ly resembles Protitan grangeri and Protitan minor, but it can be most easily distinguished from these species by the smaller, less subcaniniform incisors and tube-shaped ex- ternal auditory pseudomeatus. Additionally, Protitanotherium emarginatum is distinct from Diplacodon elatus in its relatively smaller horns, dorsoventrally shallow nasal incision, less deeply saddle-shaped cranium, differently shaped nasal process, and less molarized premolars.