Abstract

Ecological opportunity arising in the aftermath of mass extinction events is a powerful driver of evolutionary radiations. Here, we assessed how the wake of the Cretaceous-Paleogene (K-Pg) mass extinction shaped taxonomic proliferation, phe-notypic disparification, and ecological diversification in a group of mostly marine acanthomorph fishes—the Carangaria. This clade comprises a disparate array of benthic and pelagic dwellers (ca. 1100 species), including some of the most aston-ishing forms and critical components of the Caribbean fish fauna such as flatfishes, billfishes, remoras, and barracudas. We estimated a fossil-calibrated multi-locus time tree that covers all major lineages in the group and used a set of phylogenetic comparative approaches to investigate how rates of lineage diversification, multivariate phenotypic evolution, and habitat transitions vary throughout the history of the clade. Analyses of lineage diversification show time-heterogeneous rates of taxonomic diversification in carangarians, with the highest levels of diversity reached during the Paleocene. Likewise, a remarkable proportion of Carangaria’s morphological variation originated early in the history of the group and in tandem with a marked incidence of habitat shifts. Taken together, these results suggest that all major lineages and body plans in Carangaria originated in an early burst shortly after the K-Pg mass extinction, which ultimately allowed the occupation of newly released niches along the benthic-pelagic axis.

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