Anomoeodus

Anomoeodus is an extinct genus of prehistoric marine ray-finned fish belonging to the family Pycnodontidae. This genus primarily lived during the mid-to-late Cretaceous period, ranging from the Albian to the very end of the Maastrichtian age, and possibly into the Danian. The first fossils of Anomoeodus were described by Louis Agassiz in 1833, although they were described under Pycnodus. Some studies have recovered it as a wastebasket taxon.

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.

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 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 in New Jersey, which records a mass mortality event during the Cretaceous-Paleogene extinction event, likely just after the Chicxulub impact. As it is located slightly above the Cretaceous-Paleogene boundary, it is technically in the very earliest Danian. 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
Anomoeodus was one of the largest genera of Pycnodontiformes, with some species reaching up to 1 meter (3.3 ft) in length. It had a deep and laterally compressed body, with a relatively small head and a large dorsal fin. 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.

Anomoeodus had a distinctive morphology that allowed it to be easily identified. The genus had an elongated dorsal fin, which was positioned far back on its body, and a long anal fin. Its pectoral fins were relatively small, while the pelvic fins were positioned far back on the body. The scales of Anomoeodus were large and thick, with a distinctive concentric growth pattern.

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:

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.
 * A. aegypticus Capasso et al, 2021 - Maastrichtian of Egypt
 * A. angustus (Agassiz, 1844) - Cenomanian of the United Kingdom, Czech Republic and Germany (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
 * A. cenomanicus (Sauvage, 1872)
 * A. caddoi Suarez et al., 2021 - Albian of Arkansas
 * A. confertus Woodward, 1895
 * A. couloni (Agassiz, 1843)
 * A. cottreaui Priem, 1912
 * A. disparilis (Cornuel, 1877)
 * A. distans (Coquand, 1860)
 * A. fraiponti Forir, 1889
 * A. hunteri
 * A. latidens Gidley, 1913 - Campanian to Maastrichtian of Maryland, Mississippi, and New Jersey
 * A. mississippiensis Gidley, 1913 - Cretaceous of Mississippi
 * A. muensteri (Agassiz, 1834) - Cenomanian of Germany (syn: Pycnodus depressus Agassiz, 1844, P. complanatus Agassiz, 1844 )
 * A. obliquus (Pictet & Campiche, 1858)
 * A. pauciseriale - Kriwet, 2002 - Cenomanian of the United Kingdom
 * A. phaseolus (Hay, 1899) - Coniacian to Maastrichtian/Danian boundary of Delaware, Georgia, Maryland, Mississippi, New Jersey, North Carolina, and South Carolina (syn: Pycnodus faba Leidy, 1872 )
 * A. robustus (Leidy, 1857)
 * A. sculptus (Cornuel, 1877) (syn: Pycnodus imitator Cornuel, 1877 )
 * A. splendidus - Nessov, 1985 - Cenomanian of Uzbekistan
 * A. subclavatus (Agassiz, 1844) - Campanian of Sweden, Maastrichtian of the Netherlands (type species)
 * A. superbus Woodward, 1893
 * A. willetti Woodward, 1893 - Cenomanian of the United Kingdom
 * A. wolfi Capasso, 2020 - Cenomanian of Texas
 * A. woodwardi Sauvage, 1898 - Cretaceous of Portugal

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 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 are believed to have been able to tolerate brackish water 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 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.