Evolution of the ray-finned fish brain revealed through exceptional fossil preservation

Ray-finned fishes (actinopterygians) today account for over half of all living vertebrates, and their origins date back over 300 million years. With over 30,000 species, they represent the largest vertebrate group and encompass everything from goldfish to seahorses and tuna to sunfish. Ray-finned fishes display an array of morphological innovations, key among which are features of the brain. There are several challenges to understanding how—and when—these innovations evolved, not least that living ray-finned fishes are evolutionarily remote from their early ancestors, and soft tissue structures rarely fossilise. Propagation phase contrast synchrotron X-ray μCT of 319-million-year fossil fish that exceptionally preserve neural tissues within the skull – such as the brain and cranial nerves – will open a window into brain evolution early in the group’s history. The findings from this work will clarify patterns of evolution and innovation outside of the living group.