Diversification dynamics of the Palaeozoic actinopterygian radiation

Abstract

Ray-finned fish are the most speciose vertebrate group today, but the dynamics of their early diversification are contentious. Their fossil record suggests a first radiation in the Carboniferous following the Late Devonian mass extinction events. Conversely, recent phylogenetic hypotheses imply a radiation originating in the Late Devonian, but lack the taxonomic breadth required to robustly test this. This necessitates phylogeny-free inference of actinopterygian diversification rates from fossil occurrences, itself challenging due to complex systematics, incomplete occurrence databases, and severe spatiotemporal sampling biases. Here, we analyse a comprehensive dataset of Palaeozoic actinopterygian genera and species using approaches that accommodate spatial and temporal sampling variation. We detect elevated actinopterygian diversification in the Late Devonian, with substantially greater lineage survival across the Hangenberg extinction event than indicated by the raw fossil record. Surprisingly, we detect no positive shifts in origination across the event, refuting previous hypotheses of explosive actinopterygian radiation in its wake. Instead, cryptic survival of diversified lineages appears responsible for the robust signal of increased diversity across different geographic scales in the Carboniferous. Nonetheless, these trends are overwhelmingly driven by low palaeolatitude Euramerican fossil assemblages, highlighting the ongoing spatial limitations of the actinopterygian fossil record.