Body size evolution and habitat colonization across 100 million years (Late Jurassic–Paleocene) of the actinopterygian evolutionary history

Fishes are characterized by their capacity to occupy all aquatic environments and by their amazing range of size and morphology. While it is known that habitat influenced the diversity dynamics of fish clades, studies on environmental colonization events through the evolutionary history of ray‐finned fishes have yielded conflicting results as to the origin of modern clades and preferential directions of shifts. The effects of habitat over morphological evolution such as body size remain poorly known in vertebrates. However, body size evolution is more frequently addressed in terms of variation through time and numerous studies have demonstrated that successive taxa within a clade tend to increase in size through time (Cope's or Depéret's rule). We use phylogenetic comparative methods on a genus‐level actinopterygian super‐tree based on extant and fossil data covering the Late Jurassic‐Paleogene interval. Results indicate marine ancestry for freshwater lineages and a dominance of colonizations from marine clades towards other habitats. Similar trends in environment occupancy among different ray‐finned clades are explored. Three main trends affecting non‐closely‐related clades are recognized: (i) the freshwater invaders, (ii) the predominantly marine dwellers and (iii) the environmentally labile fishes. Habitat effects on body size evolution are not statistically supported, but most actinopterygian subclades originate from small‐sized ancestors and tend to increase in size in the course of their evolutionary history. This trend is clear for lineages restricted for long periods of time in the same environments, either marine or freshwater, but it is not observed in environmentally labile fish lineages.