Osteichthyes are a taxonomic grouping of bony fishes. This group includes ray-finned fishes (class: Actinopterygii) and lobe-finned fishes (class: Sarcopterygii). This highly diverse group of fishes, which contains almost all fish species, is the most diverse group of vertebrates today. Osteichthyes differ from chondrichthyes by (in most cases) possessing a bony skeleton, a swim bladder, scales (ctenoid, cycloid, or ganoid scales), and external fertilization.
Teleosts are the most diverse group of fishes (over 26,500 extant species). Over half of all living vertebrate species are teleosts. Teleosts are characterized by a protrusible jaw (musculature gives them the ability to move their maxilla and premaxilla) and a symmetrical tail (their spine that ends at the caudal peduncle unlike, for example, sharks). Teleosts are estimated to have evolved during the Triassic period. By the end of the Cretaceous, the fossil record shows that teleosts dominated both freshwater and marine habitats.