Timeline of fish evolution

The evolution of fishes took place over a timeline which spans the Cambrian to the Cenozoic, including during that time in particular the Devonian, which has been dubbed the "age of fishes" for the many changes during that period.

The Late Devonian extinctions played a crucial role in shaping the evolution of fish, or vertebrates in general. Fishes evolved during the Early Paleozoic; by the Devonian, all modern groups (Agnatha, Chondrichthyes, and Osteichthyes) were already present. Devonian aquatic environments were also marked by placoderms and acanthodians, which are only known from fossils, however. After suffering large losses during the Late Devonian extinctions, cartilaginous fishes (Chondrichthyes) and the Actinopterygii among the bony fishes (Osteichthyes) diversified.

The sections below describe the pre-Devonian origin of fish, their Devonian radiation, including the conquest of land by early tetrapods, and the post-Devonian evolution of fishes.