Sampling biases obscure the early diversification of the largest living vertebrate group

Extant ray-finned fishes (Actinopterygii) dominate marine and freshwater environments, yet their spatiotemporal diversity dynamics following their origin in the Palaeozoic are poorly understood. Previous studies investigate face-value patterns of richness, with only qualitative assessment of potential biases acting on the Palaeozoic actinopterygian fossil record. Here, we investigate palaeogeographic trends and apply richness estimation techniques to a recently-assembled occurrence database for Palaeozoic ray-finned fishes. We reconstruct patterns of local richness of Palaeozoic actinopterygians, alongside sampling standardised estimates of ‘global’ diversity. We identify substantial fossil record biases, such as geographic bias in the sampling of actinopterygian occurrences centred around Europe and North America. Similarly, estimates of diversity are skewed by extreme unevenness in the abundance distributions of occurrences, reflecting past taxonomic practices and historical biases in sampling. Increasing sampling of poorly represented regions and expanding sampling beyond the literature to include museum collection data will be critical in obtaining accurate estimates of Palaeozoic actinopterygian diversity. In conjunction, applying diversity estimation techniques to well-sampled regional subsets of the ‘global’ dataset may identify accurate local diversity trends.