What began as a clade of fleshy-finned aquatic forms, Sarcopterygii today includes all land-dwelling vertebrates—amphibians, reptiles, birds, and mammals—alongside a few remaining fish like coelacanths and lungfish.

The ancestral members of the group are united by paired limbs supported by a robust internal skeleton, including bones homologous to limbs in tetrapods. These fleshy, lobed fins mark a key distinction from the ray-supported fins of their Actinopterygian relatives. In modern Sarcopterygians such as mammals or birds, these fins have transformed into true limbs, or been secondarily modified or lost altogether.

Sarcopterygians first appear in the Silurian period. The group’s evolutionary legacy includes the origin of digits, lungs, and internal nostrils—traits that first evolved in aquatic ancestors and laid the groundwork for life on land.