Actinopterygii

Actinopterygii

A group of bony fishes, also known as actinops or ray-finned fishes, containing about half of all vertebrate species and about 96% of all living “fishes” (a nonmonophyletic group derived from more than one lineage when tetrapods are excluded). Living Actinopterygii comprise Polypteriformes (bichirs and reedfish), Acipenseriformes (sturgeons and paddlefishes), Lepisosteiformes (gars), Amiiformes (bowfins), and Teleostei (teleosts). Actinops are characterized by the presence of a single dorsal fin, an enclosed sensory canal in the dentary bone, a specialized tissue called ganoin, and several other anatomical characters. About 40% of living actinopterygian species live exclusively or almost exclusively in fresh water. The rest inhabit mostly marine, brackish, or combination environments.

The fossil record indicates that actinopterygians are at least as old as the Late Silurian (about 420 million years before present). Fossil actinopterygians are speciose and extremely abundant, making up the majority of vertebrate fossils that are known by complete skeletons. Many major radiations of early actinopterygians, such as pycnodonts, semionotiforms, and palaeonisciforms, have been extinct for tens of millions of years. Other early actinopterygian groups, such as the Cheirolepiformes, have been extinct for hundreds of millions of years. Based on the fossil record, the most major differentiation of the group began in the late Mesozoic.