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Metarhinus diploconus

Mammalia - Perissodactyla - Brontotheriidae

Taxonomy
Telmatotherium diploconum was named by Osborn (1895). Its type specimen is AMNH 1863, a skull (skull (No. 1863) in which the nasals are wanting and the mid-region of the cranium was crushed), and it is a 3D body fossil.

It was recombined as Rhadinorhinus diploconum by Riggs (1912), Osborn (1929) and Mader (1989); it was recombined as Fossendorhinus diploconus by Mihlbachler (2008); it was recombined as Metarhinus diploconus by Osborn (1908), Mader (1998) and Mader (2008).

Synonyms
Synonymy list
YearName and author
1895Telmatotherium diploconum Osborn p. 85 fig. 6
1908Metarhinus diploconus Osborn
1912Rhadinorhinus abbotti Riggs
1912Rhadinorhinus diploconum Riggs
1912Rhadinorhinus abbotti Riggs p. 36
1929Rhadinorhinus diploconum Osborn
1989Rhadinorhinus diploconum Mader
1998Metarhinus diploconus Mader
2008Metarhinus diploconus Mader p. 8
2008Fossendorhinus diploconus Mihlbachler

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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
RankNameAuthor
Synapsida()
Therapsida()
infraorderCynodontia()
Epicynodontia
infraorderEucynodontia
Probainognathia
Mammaliamorpha
Mammaliaformes
classMammalia
subclassTribosphenida()
infraclassEutheria()
Placentalia
orderPerissodactyla()
familyBrontotheriidae()
subfamilyBrontotheriinaeMarsh 1873
genusMetarhinus
speciesdiploconus()

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 1895Superior premolar-molar series,174mm. A large hypocone upon last upper molar. Naso-frontals without horn. Long sagittal crest. Canines small, rounded.
M. C. Mihlbachler 2008Fossendorhinus diploconus is an intermediate-sized hornless brontothere. The nasal incision extends posteriorly as far back as the anterior margin of the M1. The orbits are positioned above the M2 and protrude laterally, though not to the degree seen in Metarhinus. The premaxilla is robust and does not contact the nasal bone. The premaxillomaxillary rostral cavity is open dorsally and there are two large fossae inside the nasal chamber. The premaxillomaxillary rostrum is strongly upturned and is relatively constant in thickness throughout its length. Other cranial features include a well-devel- oped sagittal crest, a strongly concave mid- cranial dorsal surface, a strongly convex posterior dorsal surface, thin and strongly curved zygomatic arches, and a ventrally open and mediolaterally directed external auditory pseudomeatus.
Dentally, Fossendorhinus diploconus has three large upper incisors, a distinct P2 metacone, weak premolar preprotocristae, short lingual crests extending posteriorly from the premolar protocones, and small hypocones on P2 and P3. 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 and an anterolingual cingular cusp are absent. Cen- tral molar fossae are present. All traces of molar paraconules and metalophs are lost.
Fossendorhinus diploconus is most similar to Metarhinus, but can be clearly differenti- ated from Metarhinus by the autapomorphic fossae inside the nasal chamber, the less laterally protruding orbits, and the more strongly upturned rostrum.