''Njoerdichthys'' is an extinct genus of pycnodontid

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

from the

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 ...

Hesseltal Formation in Germany.

Discovery and naming

The original holotype of ''Njoerdichthys'' was discovered in 1995 at the abandoned Galgenknapp quarry, previously owned by the Dyckerhoff AG company, while the paratype specimens were discovered in the Hohne quarry, also owned by the company, located west of Lengerich, Germany. The specimens were found in laminated marlstones. Both quarries are part of the

Late 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 ''cre ...

Hesseltal Formation. All of the specimens where collected and then prepared by Udo Resch, who is famous for his fossil preparating skills. The name of ''Njoerdichthys'' refers to the ancient Germanic god Njörd, who, in German mythology, navegates the waters and winds, plus the Greek name "ichthyos", meaning fish. The name of the species, ''N. dyckerhoffi'', refers to the Dyckerhoff AG company.

Description

''Njoerdichthys'' was a small fish, the holotype being 4.2 cm long. The specimens comprise skeletons more or less complete, with the holotype preserving both cranial and postcranial remains, as does the paratypes, which consists of a larger specimen and a juvenile. Despite lacking a postparietal process, phylogenetic analysis still finds it a part of the

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 ...

family, in the Nursalliinae subfamily.

Paleoenvironment

''Njoerdichthys'' is the most northerly pycnodontiform recorded from the Cretaceous, living in a marine environment during the early

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), ...

, when temperatures peaked their highest during the Mesozoic. This, with the discovery of Anomoedus in

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

, is additional evidence to pycnodontids having expanded into higher latitudes with the warming of the climate and that climate played a crucial role in their expansion.

References

{{Taxonbar, from=Q123058380 Pycnodontiformes genera Cretaceous fish of Europe Late Cretaceous bony fish Turonian genera Fossils of Germany Fossil taxa described in 2020 Monotypic prehistoric ray-finned fish genera