The early evolution of ray‐finned fishes

Ray‐finned fishes ( A ctinopterygii) constitute approximately half of all living vertebrate species. A stable hypothesis of relationships among major modern lineages has emerged over the past decade, supported by both anatomy and molecules. Diversity is unevenly partitioned across the actinopterygian tree, with most species concentrated within a handful of geologically young (i.e. C retaceous) teleost clades. Extant non‐teleost groups are portrayed as ‘living fossils’, but this moniker should not be taken as evidence of especially primitive structure: each of these lineages is characterized by profound specializations. Attribution of fossils to the crowns and apical stems of C ladistia, C hondrostei and N eopterygii is uncontroversial, but placements of P alaeozoic taxa along deeper branches of actinopterygian phylogeny are less secure. Despite these limitations, some major outlines of actinopterygian diversification seem reasonably clear from the fossil record: low richness and disparity in the D evonian; elevated morphological variety, linked to increases in taxonomic dominance, in the early C arboniferous; and further gains in taxonomic dominance in the E arly T riassic associated with earliest appearance of trophically diverse crown neopterygians.