Teleosts

Abstract

The first teleosts appeared in the Upper Jurassic, probably in the sea. They radiated during the Cretaceous, invading every marine habitat from shore-line to the abyss, and also fresh water where they became the dominant fishes. Most of the major groups of modern bony fishes had evolved by the Eocene period. Their success is due to many factors, particularly the modification of the lung as the swim bladder for buoyancy. Adjustment of the gas pressure in the swim bladder allows the fish to remain at rest at a wide range of depths. A common feature of many teleosts, which leads to highly manoeuvrable and rapid swimming, is the relatively short compressed body, with thin dermal scales and a symmetrical (homocercal) tail.