''Anomoeodus'' is an extinct genus of prehistoric marine

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 ...

belonging to the family

Pycnodontidae Pycnodontidae is an extinct family of ray-finned fishes, ranging from the Jurassic period until the Late Eocene. It was the largest and most derived family of the successful Mesozoic fish order Pycnodontiformes, and one of only two families (alon ...

. This genus primarily lived during the mid-to-late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period, ranging from the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

to the very end of the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

age, and possibly into the

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretac ...

. The first fossils of ''Anomoeodus'' were described by Louis Agassiz in 1833, although they were described under ''

Pycnodus ''Pycnodus'' (from , 'dense' and 'tooth') is an extinct genus of Actinopterygii, ray-finned fish from the Eocene period. It is a wastebasket taxon, although many fossils from the Jurassic or Cretaceous are assigned to this genus, only the Eoce ...

''. Some studies have recovered it as a

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...

. In the United States, fossil teeth of the widespread species ''A. phaseolus'' are colloquially referred to as "drum fish" teeth due to their close resemblance to those of modern drumfish. However, they are unrelated to actual drumfish, which only appeared during the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

Distribution

''Anomoeodus'' had a wide geographic distribution, with fossils found in France, Belgium, the Netherlands, Spain, Egypt, Uzbekistan, and the United States. Remains of the species ''A. subclavatus'' are known from the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

of the Kristianstad Basin in Sweden, making it one of the northernmost-occurring pycnodont taxa. This northwards migration may be associated with the warming temperatures of the time. ''A. phaseolus'' teeth are known from the Main Fossiliferous Layer (MFL) of the

Hornerstown Formation The Hornerstown Formation is a latest Cretaceous to early Paleocene-aged geologic Formation (geology), formation in New Jersey. It preserves a variety of fossil remains, including those of dinosaurs, and contains direct evidence of the Mass morta ...

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

, which records a mass mortality event during the Cretaceous-Paleogene extinction event, likely just after the

Chicxulub impact The Chicxulub crater is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore, but the crater is named after the onshore community of Chicxulub Pueblo (not the larger coastal town of Chicxulub Puerto). I ...

. As it is located slightly above the Cretaceous-Paleogene boundary, it is technically in the very earliest

. In any case, their presence indicates that ''Anomoeodus'' existed up until the Cretaceous/Paleocene boundary, and these fossils represent the latest records for the taxon. A single tooth is located slightly above the boundary, which may indicate that ''Anomoeodus'' survived further into the early Danian, but this tooth may have been reworked from earlier layers.

Description

Like many members of its family, ''Anomoeodus'' had strong jaws and teeth adapted for crushing hard prey, making it mainly durophagous. Its diet is believed to have consisted primarily of crustaceans and mollusks. Diagnostic features of this genus include teeth that are generally spherical, kidney-shaped, or elliptical, as well as the presence of four tooth rows in a jaw.

Species

The following species are known: * ''A. aegypticus'' Capasso ''et al'', 2021 -

of Egypt ( Dakhla Formation) * ''A. angustus'' (

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 ...

, 1844) -

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

of the United Kingdom ( English Chalk),

Czech Republic The Czech Republic, also known as Czechia, and historically known as Bohemia, is a landlocked country in Central Europe. The country is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the south ...

and Germany (

Hesseltal Formation The Hesseltal Formation or Blackcoloured Formation is a Late Cretaceous (late Cenomanian to early Turonian) geological formation from northern Germany. It consists of lithified marls and limestone, with a unique series of black shales deposited ...

) (syn: ''Pycnodus cretaceus'' Agassiz, 1844, ''P. elongatus'' Agassiz, 1844, ''P. rhomboidalis'' Agassiz, 1844, ''P. subdeltoideus'' Reuss, 1845) * ''A. aulercus'' (Sauvage, 1872) * ''A. carteri'' Woodward, 1895 - Cenomanian of England (

Cambridge Greensand The Cambridge Greensand is a geological unit in England whose strata are earliest Cenomanian in age. It lies above the erosive contact between the Gault Formation and the Chalk Group in the vicinity of Cambridgeshire, and technically forms the l ...

) * ''A. cenomanicus'' (Sauvage, 1872) * ''A. caddoi'' Suarez ''et al.'', 2021 -

of Arkansas, US ( Holly Creek Formation) * ''A. confertus'' Woodward, 1895 - Cenomanian of England (Cambridge Greensand) * ''A. couloni'' (Agassiz, 1843) - Late Cretaceous of Europe (''nomen dubium'') * ''A. cottreaui'' Priem, 1912 * ''A. disparilis'' (Cornuel, 1877) - Early Cretaceous of France (''nomen dubium'') * ''A. distans'' (Coquand, 1860) - Late Cretaceous of France * ''A. fraiponti'' Forir, 1889 - Maastrichtian of the Netherlands (

Maastricht Formation The Maastricht Formation (Dutch language, Dutch: ''Formatie van Maastricht''; abbreviation: MMa), named after the city of Maastricht in the Netherlands, is a geological Formation (geology), formation in the Netherlands and Belgium whose strata dat ...

) * ''A. hunteri'' * ''A. latidens'' Gidley, 1913 -

to Maastrichtian of Maryland ( Monmouth Group), Mississippi, & New Jersey ( Navesink Formation), US * ''A. mississippiensis'' Gidley, 1913 - Cretaceous of Mississippi, US * ''A. muensteri'' (Agassiz, 1834) - Cenomanian of Germany (Hesseltal Formation) (syn: ''Pycnodus depressus'' Agassiz, 1844, ''P. complanatus'' Agassiz, 1844) * ''A. obliquus'' ( Pictet & Campiche, 1858) - Albian of Switzerland (''nomen dubium'') * ''A. pauciseriale -'' Kriwet, 2002 - Cenomanian of England (English Chalk) * ''A. phaseolus'' (

Hay Hay is grass, legumes, or other herbaceous plants that have been cut and dried to be stored for use as animal fodder, either for large grazing animals raised as livestock, such as cattle, horses, goats, and sheep, or for smaller domesticate ...

, 1899) ''-''

Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by ...

to Maastrichtian/

boundary of Delaware (

Marshalltown Formation The Marshalltown Formation is a Late Cretaceous (Campanian)-aged geologic Formation (geology), formation in New Jersey and Delaware, US. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the format ...

), Georgia ( Blufftown & Cusseta Formations), Maryland (

Severn Formation The Severn Formation is a Mesozoic geologic formation in Maryland. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. ...

), Mississippi (

Eutaw Formation The Eutaw Formation is a geological Formation (geology), formation in North America, within the United States, U.S. states of Alabama, Georgia (U.S. state), Georgia, and Mississippi. The strata date from the late Coniacian to the early Santonian S ...

), New Jersey (Marshalltown, Mount Laurel, Wenonah, Navesink & Hornerstown Formations) North Carolina (

Tar Heel Tar Heel (or Tarheel) is a nickname applied to the U.S. state of North Carolina and its people. It is also the nickname of the University of North Carolina athletic teams, students, alumni, and fans. The origins of the Tar Heel nickname trace ba ...

& Bladen Formations), and South Carolina ( Donoho Creek Formation), US (syn: ''Pycnodus faba'' Leidy, 1872) * ''A. robustus'' (Leidy, 1857) - Early Cretaceous of France * ''A. sculptus'' (Cornuel, 1877) (syn: ''Pycnodus imitator'' Cornuel, 1877) - Early Cretaceous of France * ''A. splendidus'' Nessov, 1985 ''-'' Cenomanian of

Uzbekistan , image_flag = Flag of Uzbekistan.svg , image_coat = Emblem of Uzbekistan.svg , symbol_type = Emblem of Uzbekistan, Emblem , national_anthem = "State Anthem of Uzbekistan, State Anthem of the Republ ...

( Khodzhakul Formation) * ''A. subclavatus'' (Agassiz, 1844) (

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

) ''-'' Campanian of Sweden ( Kristianstad Basin), Maastrichtian of the Netherlands & Belgium (Maastricht Formation) * ''A. superbus'' Woodward, 1893 - Cenomanian of England (Cambridge Greensand) * ''A. willetti'' Woodward, 1893 - Cenomanian of England (English Chalk) * ''A. wolfi'' Capasso, 2020 - Cenomanian of Texas ( Del Rio Formation) * ''A. woodwardi'' Sauvage, 1898 ''-'' Cretaceous of Portugal The majority of these species are only known from isolated dental elements. Only a few species (''A. angustus'', ''A. willetti'', ''A. subclavatus'', ''A. pauciseriale'') are known from more than just teeth. Cooper & Martill (2020) determined that a diagnostic feature of ''Anomoeodus'' is the presence of 4 tooth rows, excluding several former species. The former species ''A. barberi'' has been reclassified into the genus '' Agassizilia'' due to having more than 5 tooth rows, and the former species "''A''" ''nursalli'' Kriwet, 1999 is now considered an indeterminate pycnodontid due to having 6 tooth rows. Further taxonomic revisions are likely required for this genus.

Fossil record

Fossils of ''Anomoeodus'' have been found in marine deposits from the Late Cretaceous period. In North America, they have been found in the

Niobrara Formation The Niobrara Formation , also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late Cretaceous. It is com ...

in Wyoming and South Dakota, and the Eagle Ford Formation in Texas. In Europe, ''Anomoeodus'' fossils have been found in the Upper Cretaceous strata of Spain, Belgium, the Netherlands, France, and Uzbekistan. In Africa, fossils have been found in Egypt and Morocco.

Paleoecology

''Anomoeodus'' lived in a variety of marine environments, from shallow coastal waters to deeper offshore environments. It is believed to have been a relatively common component of Cretaceous marine faunas. Some species (such as ''A. caddoi'') are believed to have been able to tolerate estuarine environments, while others are only known from offshore marine deposits. It is generally thought to have been a reef fish. In addition to its role as a predator of crustaceans and mollusks, ''Anomoeodus'' likely served as a prey item for larger marine predators, such as

mosasaurs Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains were discovered in ...

and sharks. The thick scales and heavily armored head of ''Anomoeodus'' likely provided some protection from predation, although it is unknown how effective this defense mechanism was in practice.

References