'Fish' (Actinopterygii and Elasmobranchii) diversification patterns through deep time

Actinopterygii (ray-finned fishes) and Elasmobranchii (sharks, skates and rays) represent more than half of today's vertebrate taxic diversity (approximately 33000 species) and form the largest component of vertebrate diversity in extant aquatic ecosystems. Yet, patterns of 'fish' evolutionary history remain insufficiently understood and previous studies generally treated each group independently mainly because of their contrasting fossil record composition and corresponding sampling strategies. Because direct reading of palaeodiversity curves is affected by several biases affecting the fossil record, analytical approaches are needed to correct for these biases. In this review, we propose a comprehensive analysis based on comparison of large data sets related to competing phylogenies (including all Recent and fossil taxa) and the fossil record for both groups during the Mesozoic-Cainozoic interval. This approach provides information on the 'fish' fossil record quality and on the corrected 'fish' deep-time phylogenetic palaeodiversity signals, with special emphasis on diversification events. Because taxonomic information is preserved after analytical treatment, identified palaeodiversity events are considered both quantitatively and qualitatively and put within corresponding palaeoenvironmental and biological settings. Results indicate a better fossil record quality for elasmobranchs due to their microfossil-like fossil distribution and their very low diversity in freshwater systems, whereas freshwater actinopterygians are diverse in this realm with lower preservation potential. Several important diversification events are identified at familial and generic levels for elasmobranchs, and marine and freshwater actinopterygians, namely in the Early-Middle Jurassic (elasmobranchs), Late Jurassic (actinopterygians), Early Cretaceous (elasmobranchs, freshwater actinopterygians), Cenomanian (all groups) and the Paleocene-Eocene interval (all groups), the latter two representing the two most exceptional radiations among vertebrates. For each of these events along with the Cretaceous-Paleogene extinction, we provide an in-depth review of the taxa involved and factors that may have influenced the diversity patterns observed. Among these, palaeotemperatures, sea-levels, ocean circulation and productivity as well as continent fragmentation and environment heterogeneity (reef environments) are parameters that largely impacted on 'fish' evolutionary history, along with other biotic constraints.