Formation of beetle elytra and the most spectacular animal radiation in the history of Earth

Abstract The rise of beetles (Coleoptera) represents one of the most remarkable phenomena in the history of life. The transformation of membranous forewings into hardened elytra is widely regarded as a key innovation underpinning the extraordinary success of the group. Drawing on recent advances across multiple disciplines, we critically re-examine this long-held paradigm. Although elytra are likely to have conferred early coleopteran ancestors with crucial adaptive advantages, allowing them to penetrate wood-related niches without damaging the vulnerable hindwings and internal organs, analogous structures in other insect groups have not been drivers of comparable diversification or lineage persistence. Notably, the initial emergence of elytra did not coincide with rapid beetle diversification; instead, significant radiations followed key secondary modifications of these structures. We propose that the high potential of elytra for evolutionary modification, manifested in a wide array of innovations and associated neo-functionalizations, has enhanced the potential for subsequent evolutionary radiations of beetles. Elytra formation seems to be a crucial precondition of coleopteran diversification, and their high evolutionary plasticity was one of the key factors enabling beetles to enter a variety of new adaptive zones. A synergistic confluence of various extrinsic factors within some of the adaptive zones has sparked an explosion of species richness in certain branches.