Key innovations are thought to promote the diversification of lineages by allowing them to exploit their environment in a previously unexplored way. The more popular interpretation, defined by a trait that provides access to novel resources, excludes innovations which merely increase the rate of diversification or levels of phenotypic diversity. Restricted gill openings (RGOs) are a modification of the teleost branchiostegal membrane which results in smaller gill openings, which may free up the evolution of bones and tissues that were previously constrained by gill size and shape. Here we use 3D geometric morphometrics and phylogenetic comparative methods to investigate the influence of branchiostegal membrane state on skull shape evolution in Actinopterygii. We find higher rates of evolution in lineages with RGO than other gill membrane states, and varying levels of disparity across states.