Sarcopterygii (lobe‑finned fishes)

Characteristics

Sarcopterygians share several anatomical traits: robust fin lobes with internal bone structures homologous to tetrapod limb bones, paired appendages, and in many groups primitive lungs or lung‑like organs. Externally they can vary from the scaled, deep‑bodied lungfishes to the streamlined, rare coelacanths. Examples include the lungfish, which can breathe air, and the coelacanths, noted for their distinctive fin placement.

Evolutionary history

The group first appears in the fossil record in the Silurian period and diversified through the Devonian. During that long history, several sarcopterygian lineages produced forms adapted to shallow, vegetation‑choked waters; one of these later evolved adaptations for weight‑bearing limbs and digits. That transition is the origin of the tetrapods, the vertebrate group that includes amphibians, reptiles, birds and mammals.

Living groups and notable facts

Today only a few sarcopterygian lineages survive. Modern lungfishes live in freshwater and can survive dry seasons by estivating; coelacanths are deep‑water fishes once thought extinct and later rediscovered. Fossils of many extinct forms document the gradual anatomical changes that link fish to early land vertebrates.

Significance and classification

Sarcopterygii are central to understanding vertebrate evolution. In contemporary classifications the term may be used narrowly for the lobe‑finned fishes or more broadly to include tetrapods, reflecting the evolutionary continuity from fin to limb. They stand in contrast to the ray‑finned fishes (Actinopterygii), which have a very different fin structure and represent the other great lineage of bony fishes.