Acrotemnus

 ( Pycnodontiformes Genera ) 

Acrotemnus is an extinct genus of marine Pycnodontidae ray-finned fish known from Europe, North America, and Africa during the Turonian stage of the Upper Cretaceous. North American species could reach comparatively giant sizes for pycnodonts.

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Taxonomy The following species are known:

• A. faba Louis Agassiz, 1836 - Turonian of England (Chalk Group)L. Agassiz. 1836. Recherches Sur Les Poissons Fossiles. Tome I (livr. 18). Imprimerie de Petitpierre, Neuchatel
• A. megafrendodon (Shimada, Williamson & Sealey, 2010) - Turonian of New Mexico, USA (Mancos Shale) (= Macropycnodon megafrendodon Shimada, 2010)
• A. streckeri (Hibbard, 1939) - Turonian of Kansas (Carlile Shale), potentially Texas (Boquillas Formation) (= Coelodus streckeri Hibbard, 1939)

An indeterminate potential species is also known from the Turonian of Nigeria (Benue Trough).

Acrotemnus was initially known from just the type species A. faba described by Louis Agassiz in 1843 from specimens collected in England. In 1939, Hibbard described a large-sized pycnodont from a tooth plate from Kansas, which he placed in Coelodus as C. streckeri. In 2010, Shimada, Williamson & Sealey described a gigantic pycnodont known from a few tooth plates found in New Mexico as Macropycnodon megafrendodon, placing C. streckeri in the same genus. However, in 2021, Shimada, Portillo, and Cronin described a partial skeleton of a pycnodont from Texas as potentially being a specimen of A. streckeri. This specimen revealed close similarities between the anatomy of Macropycnodon and Acrotemnus, leading to the lumping of the former into the latter.

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Description A. megafrendodon is known from isolated teeth, the largest being in width. A comparision between the tooth-to-body size ratio of more completely known relatives, such as Coelodus, suggests that A. megafrendodon could have reached comparatively gigantic body sizes of over . This would make it among the largest pycnodonts, especially given that the majority do not reach over in length. The partial specimen of A. cf. streckeri described in 2021 is estimated to have been roughly in length, supporting these estimates.

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See also

• Prehistoric fish
• List of prehistoric bony fish

Categories: Pycnodontiformes Genera, Prehistoric Ray-finned Fish Genera, Turonian Genera, Late Cretaceous Bony Fish, Late Cretaceous Fish Of North America, Cretaceous Fish Of Europe, Late Cretaceous Fish Of Africa, Fossils Of England, Fossils Of The United States, Fossils Of Nigeria, Fossil Taxa Described In 1836, Taxa Named By Louis Agassiz

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