Teleost Fishes (Teleostei) is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in theTriassic period, includes 26,840 extant species in about 40 orders and 448 families; most living fishes are members of this group. The other two infraclasses, Holostei and Chondrostei, may be paraphyletic.
Some teleost fish have also developed jet propulsion, passing water through the gills to supplement fin-driven motion.
The oldest teleost fossils date back to early Triassic, possibly evolving from fish related to the bowfin in the clade Holostei. During the Mesozoic and Cenozoic they diversified and as a result, 96% of all known fish species are teleosts. Teleosts are here divided into twelve superorders, but this system is unlikely to be entirely correct and is in the process of being studied.