''Acrotemnus'' is an extinct genus of marine pycnodontid

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

known from Europe, North America, and Africa during the

Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cret ...

. North American species could reach comparatively giant sizes for pycnodonts.

Taxonomy

The following species are known: * ''A. faba''

Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he recei ...

, 1836 -

of England ( English Chalk)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 The Mancos Shale or Mancos Group is a Late Cretaceous (Upper Cretaceous) geologic formation of the Western United States. The Mancos Shale was first described by Cross and Purington in 1899 and was named for exposures near the town of Mancos, C ...

) (=''Macropycnodon megafrendodon'' Shimada, 2010) * ''A. streckeri'' (

Hibbard Hibbard is a surname. Notable people with the surname include: * Aldro Hibbard (1886–1972), American painter * Bill Hibbard, American scientist * Brian Hibbard (1946–2012), Welsh actor and singer * Claude W. Hibbard (1905–1973), American pa ...

, 1939) - Turonian of Kansas (

Carlile Shale The Carlile Shale is a Turonian age Upper Cretaceous, Upper/Late Cretaceous series shale geologic Formation (geology), formation in the central-western United States, including in the Great Plains region of Colorado, Kansas, Nebraska, New Mexico ...

), potentially Texas ( Boquillas Formation) (=''Coelodus streckeri'' Hibbard, 1939) An indeterminate potential species is also known from the Turonian of Nigeria (

Benue Trough The Benue Trough is a major geological structure underlying a large part of Nigeria and extending about 1,000 km northeast from the Bight of Benin to Lake Chad. It is part of the broader West and Central African Rift System. Location The ...

). ''Acrotemnus'' was initially known from just the type species ''A. faba'' described by

Louis Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he recei ...

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.

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 saturnus'', 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.

References

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 {{Cretaceous-fish-stub

Taxonomy

Description

See also

References