Andriotis, K.; Hodge, J. R.; Brownstein, C. D.; Alfaro, M. E.; Wainwright, P. C.; Near, T. J.

Coral reefs harbour a disproportionate share of marine biodiversity, yet whether reef fish diversity reflects steady accumulation or rapid, ecologically driven diversification remains unclear. Butterflyfishes and bannerfishes (Chaetodontidae) include more than half of all coral-feeding fish species, making them a natural test of adaptive radiation on coral reefs. Here we present a time-calibrated phylogeny of 120 of the 138 species, built from 1,009 ultraconserved elements. The species-rich butterflyfishes (Chaetodontinae) are a recent radiation that originated in the Late Miocene (7.78 million years ago; 95% highest posterior density 7.13 to 8.49 million years ago), with much of their extant species diversity arising within the past 2 million years. The crown diversification rate of butterflyfishes is the highest among 29 comparator reef-fish lineages. Ancestral state reconstructions indicate that the ancestor of Chaetodontinae was a facultative corallivore, that a unique jaw joint arose before obligate corallivory, and that obligate corallivory then evolved repeatedly from facultative ancestors, alongside derived tooth morphologies. Together, these results suggest that Late Miocene coral reef turnover and the diversification of branching corals generated an ecological opportunity that functional innovations allowed butterflyfishes to exploit, extending the adaptive radiation framework to open marine seascapes beyond the island and lake systems where it has most often been applied.