Revealing the hidden patterns of shark and ray diversity over the past 145 million years

Neoselachians (a monophyletic group including modern sharks, rays, and skates and their extinct relatives)¹^,² have an extensive fossil record and a long evolutionary history,¹^,²^,³ with over 1,100 extant species today.⁴ Previous reconstructions of their evolutionary history suggest a diversity peak in the Cretaceous, a severe decline across the Cretaceous-Paleogene (K/Pg),⁵^,⁶^,⁷^,⁸^,⁹ and a prolonged stability thereafter,⁷^,⁸ aside from a small decline in the Pliocene.¹⁰ However, our knowledge of past neoselachian diversity has been mostly based on high taxonomic levels (e.g., genera or families),⁸ or from studies restricted to particular regions,¹¹^,¹²^,¹³ time periods,⁵^,⁹ or shark orders.¹⁴^,¹⁵ This is further complicated by spatiotemporal biases,¹⁶^,¹⁷ which can lead to apparent diversity changes, even when bias-correction methods are employed.¹⁶^,¹⁷ Using an extensive dataset of fossil occurrences¹⁸ and a deep-learning model that explicitly accounts for spatiotemporal and taxonomic sampling variation,¹⁹ we reconstruct the neoselachian diversity trajectory over the past 145 million years. We found a long-term increase during the Cretaceous, in which neoselachians reached modern diversity levels. Throughout the K/Pg, we recovered only a small (10%) decline, suggesting high turnover rather than a major extinction. Diversity then surged, culminating in a mid-Eocene peak, when neoselachians reached maximum richness. This peak was followed by a fluctuating yet downward trajectory toward the present, which overall resulted in a 41% loss of species and left modern diversity depleted compared to their thriving past. Together, our results reveal patterns hitherto obscured by multiple biases, challenging previous paradigms about neoselachian diversity.