Somewhat loosely defined term (an infraclass or superorder 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.