Chondrostei

 ( Extant Silurian First Appearances ) 

Chondrostei is a subclass of non-Neopterygii ray-finned fish. While the term originally referred to the Paraphyly grouping of all non-neopterygian ray-finned fish, it was redefined by Patterson in 1982 to be a clade comprising the Acipenseriformes (which includes sturgeon and paddlefish) and their extinct relatives.

Taxa commonly suggested to represent relatives of the Acipenseriformes include the Triassic marine fish Birgeria and the Saurichthyiformes, but their relationship with the Acipenseriformes has been strongly challenged on cladistic 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 Ptycholepiformes Boreosomus as a stem-acipenseriform.

The following taxa are known:

• Subclass Chondrostei
• Genus † Eochondrosteus
• Order †Chondrosteiformes
• Family †Chondrosteidae
• Order Acipenseriformes
• Family †Peipiaosteidae
• Suborder Acipenseroidei
• Family Sturgeon
• Family Paddlefish
• Disputed taxa include:
• Genus † Birgeria
• Family †Coccolepididae
• Order †Saurichthyiformes
• Order †Ptycholepiformes