The Evolutionary History of Early Ray-Finned Fishes (Pan-Actinopterygii)

One out of every two vertebrate species is a ray-finned fish (Actinopterygii). The ~380-million-year fossil record of ray-finned fishes provides a window into the evolutionary history of actinopterygian diversity in deep time. The actinopterygian fossil record shows that the ray-finned fish crown group (Actinopterygii) lived alongside speciose members of now extinct lineages, collectively referred to as early actinopterygians. I review the evolutionary history of early actinopterygians through deep time, including morphology, taxonomy, phylogeny, and the fossil record itself, to form a foundation for future research. Early actinopterygians are a paraphyletic assemblage of ~600 extinct species divided between ~22 named clades and the "palaeoniscoids," a taxonomic wastebasket comprised of hundreds of species. Although nearly a decade of phylogenetic research indicates that most early actinopterygians branch off the ray-finned fish stem group, their interrelationships are largely unresolved. Notable gaps in the record of early actinopterygians, which ranges from the Early Devonian to the Early Cretaceous, include a nearly non-existent Early Devonian record, an almost complete lack of Pennsylvanian-Middle Permian marine assemblages, a gap in the Middle Triassic record obscuring the start of a decline in early actinopterygian diversity, and a sparsely documented Jurassic record. We are poised to build a reliable systematic framework for early actinopterygians via novel methods for phylogenetic analysis, fossil imaging, and the increased connectivity of paleoichthyologyists around the globe. The promise of a reliable systematic framework for early actinopterygians is to better describe the entire history of Actinopterygii and actinopterygian macroevolution in deep time.