Teleostei (teleost, teleostean) Somewhat loosely defined term (an infraclass or super-order according to some authors) that includes all the living bony fish (Osteichthyes) with the exception of a few orders of primitive fish. Teleosts arose from holostean (Holostei) stock in the Jurassic. A transitional form, Leptolepis, from Upper Jurassic marine deposits, was a herring-shaped fish, around 23 cm long, with a homocercal tail and pelvic fins placed well back on the body. The scales still carried traces of enamel. Teleosts diversified in the Cretaceous and are now the most abundant vertebrate group. They exhibit a great variety of form, but are characterized by an internal skeleton entirely of bone, a reduction in thickness of the scales, and a homocercal tail; typically there is a dorsal swim bladder to control buoyancy, a mobile jaw articulation, and the fin rays may be stiffened into spines.

Teleostei (teleost, teleostean) A somewhat loosely defined term (an infraclass according to some authors) that includes all the bony fish (Osteichthyes) with the exception of a few orders of primitive fish (Acipenseriformes, Amiiformes, Semionotiformes, and their fossil relatives).

Teleostei The major superorder of the Osteichthyes (bony fish), containing about 20 000 species. Teleosts have colonized an extensive variety of habitats and show great diversity of form. The group includes the eel, seahorse, plaice, and salmon. They have been the dominant fish since the Cretaceous period (about 70 million years ago).