A clade-level morphospace for the eocene fishes of Bolca: Patterns and relationships with modern tropical shallow marine assemblages

The world-famous Eocene Konservat-Lagerstätte of Bolca, northern Italy, has been celebrated since the 16th century for its exquisitely preserved fishes, which provide the earliest evidence of a modern tropical shallow marine fish assemblage. Due to the presence of many of the earliest representatives of several modern families of reef-associated fishes, the remarkable taxonomic and morphological richness of this fish assemblage has traditionally been attributed to the presence of a coral reef system. Several studies have suggested that the broad morphological diversification of modern fish lineages may be due to the availability of greater ecological opportunity for the survivors of the end-Cretaceous mass extinction. This hypothesis was supported by a major expansion of the morphospace occupied by the fish lineages that crossed the Cretaceous-Paleogene transition, occupying regions previously inhabited by extinct Cretaceous groups. In this context, we used a geometric morphometric approach in order to describe the clade-level structure of the morphospace of the Bolca fish assemblage, and to compare the patterns of morphospace occupation and morphological diversification between the Eocene and modern tropical shallow marine fish assemblages. Although the similarity in morphospace area and the overlapping of the different convex hulls seem to indicate a relative stasis in the overall morphospace occupation from the Eocene to Recent, some differences at the clade level can be detected. In particular, the representatives of several lineages, including anguilliforms, “perciforms”, syngnathiforms and tetraodontiforms, seem to have undergone significant changes in terms of morphospace occupation, body shape variation and contribution to the overall disparity from the Eocene to today.