Did crossopterygian fish have both lungs and gills?
These fish were the early relatives of the amphibians. There were many different types showing a varied degree of amphibian traits. The early ones had gills and of course their swim bladder. As time progressed the swim bladder developed into the lungs and the gills disappeared. Here are some of these fish: 1. Osteolepis — one of the earliest crossopterygian lobe-finned fishes. They had paired fins with a leg-like arrangement of bones, and had an early-amphibian-like skull and teeth. 2. Eusthenopteron was an intermediate between early crossopterygian fish and the earliest amphibians. Their skull was very amphibian-like. They had a strong amphibian-like backbone with their fins resembeling early amphibian feet. 3. Icthyostegids were terrestrial amphibians with many of Eusthenopteron’s fish features (e.g., the fin rays of the tail were retained). Some debate about whether Icthyostega should be considered a fish or an amphibian; it is an excellent transitional fossil. 4.
