''Proacrodon'' is a dubious genus of extinct mammal from South America. Its type species is ''Proacrodon transformatus''. The only known specimen, a lower premolar or molar, is now lost, and its affinities are unknown. In 1899, Santiago Roth named the new genus and species ''Proacrodon transformatus'' on the basis of a single tooth collected in Patagonia. The genus name comes from Greek πρό "before", άκρος "pointed", and όδών "tooth", and refers to the shape of the tooth, which rises higher in its anterior portion than its posterior portion. Roth compared the taxon to ''Megacrodon'', which he named in the same paper, and to ''

Hyrachyus ''Hyrachyus'' (from '' Hyrax'' and grc, ὗς "pig") is an extinct genus of perissodactyl mammal that lived in Eocene Europe, North America, and Asia. Its remains have also been found in Jamaica. It is closely related to ''Lophiodon''.Hayden, F. ...

''.

Florentino Ameghino Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especially ...

synonymized ''Proacrodon'' with his own genus ''Trimerostephanus'' without seeing the specimen firsthand. In 1904, Palmer listed both ''Proacrodon'' and ''Trimerostephanos'' as members of

Isotemnidae Isotemnidae is an extinct Family (biology), family of Notoungulata, notoungulate mammals known from the Paleocene (Las Flores Formation, Golfo San Jorge Basin, Las Flores Formation, Itaboraian) to Middle Miocene (Honda Group, Colombia, Honda Grou ...

. In 1948 George Gaylord Simpson listed the taxon as a possible

litoptern Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinct order of fossil hoofed mammals from the Cenozoic era. The order is one of the five great orders of South American ungulates that were endemic to the continent, until th ...

and concluded that the taxon was a ''nomen vanum'', viewing Ameghino's proposal of synonymy with ''Trimerostephanos'' as possible but not reliable. The locality where the tooth was collected is not known with certainty, but was probably in the Musters Formation.

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* * * {{Taxonbar, from=Q111838977 Litopterns Nomina dubia Fossil taxa described in 1899 Prehistoric placental genera