Fossil Record

The first bony fish fossils occur in late Silurian. Fossils were abundant from the early Devonian and their major radiation was underway by mid-Devonian. In the mid-Devonian, the two major lineages diverged: the Actinopterygii (ray-finned fishes) and the Sarcopterygii (lobe-finned fishes).

The Devonian sarcopterygians included lungfishes and coelacanths, both groups still surviving. But modern lungfishes and coelacanths are a modest remnant of once-diverse groups, and they are often called 'living fossils'. The other Devonian sarcipterygians are often grouped loosely as the 'rhipidistians', a paraphyletic ('incomplete') group that includes forms such as the osteoelpiforms, tristichopterids and panderichthyids, that lie on the line of ancestry to the tetrapods.

Early actinopterygians, such as the Devonian Cheirolepis, had heavy bony scales over the whole body, and large bony plates over the head region. The jaws operated as a simple hinge, with modest movements of other skull bones to widen the gape. Late actinopterygians had more complex jaw apparatuses that allowed them to project the jaws forward and to use suction in feeding. This perhaps was one of the keys to the success of the teleosts, which arose in the Triassic or Jurassic, but radiated dramatically in the Cretaceous and Tertiary.

Fossil species from all sub-groups -the Chondrosteans, the Holosteans, the Teleosteans, Rhipidistia, Actinistia, and Dipnoi- have been identified.