''Gyrosteus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of very large

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

belonging to the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Chondrosteidae Chondrosteidae is a family of extinct marine actinopterygian fishes in the order Acipenseriformes. Three genera are known from the Early Jurassic of Europe, '' Chondrosteus'', ''Gyrosteus'', and ''Strongylosteus''. Included species were of la ...

. It comprises the type species, ''Gyrosteus mirabilis'', which lived during the early

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarc ...

(Late

Early Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma ...

) in what is now northern

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

. A possible second species, ''"Gyrosteus" subdeltoideus'', is known from otoliths. Fossil remains of ''G. mirabilis'' have been recovered from the Whitby Mudstone Formation, United Kingdom, and from Ahrensburg erratics assemblage in

Schleswig-Holstein Schleswig-Holstein (; da, Slesvig-Holsten; nds, Sleswig-Holsteen; frr, Slaswik-Holstiinj) is the northernmost of the 16 states of Germany, comprising most of the historical duchy of Holstein and the southern part of the former Duchy of Sc ...

, northern Germany. It was mentioned but not formally described in subsequent publications and was left as a ''

nomen nudum In taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published with an adequate des ...

'' for more than 25 years. Then in 1889 it was featured and formally described by Arthur Smith Woodward. ''Gyrosteus'' was thought to be exclusive of the “British faunal province” and separated from the “Germanic faunal province” until the discovery of a hyomandibula in the baltic realm, mostly populated by Germanic fauna, which possibly implicates that Baltic region represented an interdigitating zone between both regions. The members of the

''Gyrosteus'' were massive fishes, with a maximum calculated standard length of to , and with a reported hyomandibula reaching .

References

Prehistoric ray-finned fish genera Jurassic bony fish Jurassic fish of Europe Fossil taxa described in 1843 {{Jurassic-fish-stub