PBDB Taxon

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Morphology	Ecology and taphonomy	External Literature Search	Age range and collections

Diplacodon

Mammalia - Perissodactyla - Brontotheriidae

Taxonomy

Diplacodon was named by Marsh (1875). Its type is Diplacodon elatus.

It was considered a nomen dubium by Mader (2000).

It was assigned to Menodontidae by Cope (1881); to Lambdotheriinae by Hay (1902); to Diplacodontinae by Osborn (1908); to Titanotheriidae by Scott (1913); to Brontotheridae by Prothero and Schoch (1989); and to Brontotheriina by Mihlbachler (2008) and Mihlbachler (2011).

Species

D. elatus (syn. D. progressum, Eotitanotherium osborni) (type species), D. emarginatus, D. gigan

Synonyms

Eotitanotherium was named by Peterson (1914).

It was synonymized subjectively with Diplacodon by Lucas (1983) and Mihlbachler (2011).

It was assigned to Telmatheriinae by Prothero and Schoch (1989); to Brontotheridae by Peterson (1914), Carroll (1988) and Mader (1989); and to Brontotheriinae by Mader (2008).
Pseudodiplacodon was named by Mader (2000). It is not extant.

It was synonymized subjectively with Diplacodon by Mihlbachler (2011).

It was assigned to Brontotheridae by Mader (2000); and to Brontotheriinae by Mader (2008).
Diploceras was named by Peterson (1914) [preoccupied by a mollusk]. Its type is Diploceras osborni.

It was synonymized subjectively with Diplacodon by Lucas (1983); it was replaced with Eotitanotherium by Peterson (1914), Osborn (1929), Mader (1989) and Mader (2008).

It was assigned to Titanotheriidae by Peterson (1914).

Synonymy list

Year	Name and author
1875	Diplacodon Marsh p. 246
1881	Diplacodon Cope p. 397
1902	Diplacodon Hay p. 632
1908	Diplacodon Osborn p. 403
1913	Diplacodon Scott p. 291
1914	Eotitanotherium Peterson
1914	Diploceras Peterson p. 29
1914	Eotitanotherium Peterson p. 220
1988	Eotitanotherium Carroll
1989	Eotitanotherium Mader
1989	Diplacodon Prothero and Schoch p. 537
1989	Eotitanotherium Prothero and Schoch p. 537
2000	Pseudodiplacodon Mader
2008	Eotitanotherium Mader
2008	Pseudodiplacodon Mader
2008	Diplacodon Mihlbachler p. 413
2011	Diplacodon Mihlbachler

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Rank	Name	Author
kingdom	Animalia	()
—	Bilateria
—	Eubilateria	Ax 1987
—	Deuterostomia
phylum	Chordata	Haeckel 1874
subphylum	Vertebrata
superclass	Gnathostomata
—	Osteichthyes	()
subclass	Sarcopterygii	()
subclass	Dipnotetrapodomorpha	(Nelson 2006)
subclass	Tetrapodomorpha	()
—	Tetrapoda
—	Reptiliomorpha
—	Anthracosauria
subclass	Amphibiosauria	Kuhn 1967
—	Cotylosauria	()
—	Amniota
subclass	Synapsida
—	Therapsida	()
infraorder	Cynodontia	()
—	Mammaliamorpha
—	Mammaliaformes

Rank	Name	Author
class	Mammalia
—	Theriamorpha	(Rowe 1993)
—	Theriiformes	()
—	Trechnotheria
—	Cladotheria
—	Zatheria
subclass	Tribosphenida	()
subclass	Theria
—	Eutheria	()
—	Placentalia
—	Boreoeutheria
—	Laurasiatheria
—	Scrotifera
—	Euungulata
—	Panperissodactyla
superorder	Perissodactylamorpha
order	Perissodactyla	()
family	Brontotheriidae	()
subfamily	Brontotheriinae	Marsh 1873
tribe	Brontotheriini	Marsh 1873
subtribe	Brontotheriina	Marsh 1873
genus	Diplacodon

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.

G. †Diplacodon Marsh 1875

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†Diplacodon elatus Marsh 1875

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Invalid names: Diplacodon progressum Peterson 1934 [synonym], Eotitanotherium osborni Peterson 1914 [synonym]

†Diplacodon emarginatus Hatcher 1895

†Diplacodon gigan Mihlbachler 2011

Invalid names: Eotitanotherium Peterson 1914 [synonym], Pseudodiplacodon Mader 2000 [synonym]

Diagnosis

Reference	Diagnosis
B. J. Mader 2008 (Eotitanotherium)	Large-sized (length P2 to M3 approximately 221–236 mm) diplacodont brontothere with short, angular horns that are elliptical in cross-section; gracile nasals that are distally rounded and down- turned; and two well separated lingual cusps on P4. In general, the length of the cheek tooth series is longer than in most specimens of Pseudodiplacodon, but the skull is smaller in size.
B. J. Mader 2008 (Pseudodiplacodon)	Large-sized (length P2 to M3 approximately 207–234 mm) plesiomorphic diplacodont bron- tothere with bulbous horns that are roughly circular in cross-section; robust nasals that are rounded distally, curved ventrally, and shorter than in Eotitanotherium; small canines, and two poorly separated lingual cusps on P4. In general, the length of the cheek tooth series is usually shorter than in specimens of Eotitanotherium, but the skull is larger in size.
M. C. Mihlbachler 2011	Diplacodon is a horned brontothere genus most easily recognized by its distinctive nasal bone with thickened and dorsally angled (upturned) lateral margins. This trait, previously an autapomorphy of D. elatus, is now a synapomorphy of the genus. Mihlbachler’s (2008) extended diagnosis of Diplacodon elatus is now applicable to the genus Diplacodon, with the ex- ception of comments regarding size.