Chondrostei is a subclass of non- neopterygian

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 ...

. While the term originally referred to the

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

grouping of all non-neopterygian ray-finned fish, it was redefined by Patterson in 1982 to be a clade comprising the

Acipenseriformes Acipenseriformes is an order (biology), order of basal (phylogenetics), basal Actinopterygii, ray-finned fishes that includes living and fossil sturgeons and paddlefishes (Acipenseroidei), as well as the extinct family (biology), families C ...

(which includes

sturgeon Sturgeon (from Old English ultimately from Proto-Indo-European language, Proto-Indo-European *''str̥(Hx)yón''-) is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the ...

and

paddlefish Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their elongated rost ...

) and their extinct relatives. Taxa commonly suggested to represent relatives of the Acipenseriformes include the Triassic marine fish '' Birgeria'' and the

Saurichthyiformes Saurichthyiformes is an extinct order (biology), order of Actinopterygii, ray-finned fish which existed in Asia, Africa, Australia (continent), Australia, Europe and North America, during the late Permian to early Middle Jurassic. Saurichthy ...

, but their relationship with the Acipenseriformes has been strongly challenged on

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

grounds. Coccolepididae, a group of small weakly ossified Jurassic and Cretaceous fish found in both marine and freshwater environments, have also been suggested to be close relatives of the Acipenseriformes. However, this has never been subject to cladistic analysis. Near & Thacker (2024) also recovered the ptycholepiform '' Boreosomus'' as a stem-acipenseriform. The following taxa are known: * Subclass Chondrostei ** Genus †''

Eochondrosteus ''Eochondrosteus'' (meaning "dawn '' Chondrosteus''") is a genus of extinct marine actinopterygian (ray-finned fish), comprising one species, ''E. sinensis'' ( monotypy) from the Early Triassic strata in Gansu Province (Beishan Hills), China (pr ...

'' ** Order † Chondrosteiformes *** Family †

Chondrosteidae Chondrosteidae is a family (biology), family of extinct marine actinopterygian fishes, known from the Early Jurassic of Europe. They are closely related to modern Sturgeon, sturgeons and paddlefish of the order Acipenseriformes, and are either ...

** Order

*** Family † Peipiaosteidae *** Suborder Acipenseroidei **** Family

Acipenseridae Sturgeon (from Old English ultimately from Proto-Indo-European language, Proto-Indo-European *''str̥(Hx)yón''-) is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the ...

**** Family

Polyodontidae Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their elongated rost ...

* Disputed taxa include: ** Genus †'' Birgeria'' ** Family † Coccolepididae ** Order †

** Order † Ptycholepiformes

References

{{Authority control Extant Silurian first appearances Paraphyletic groups