Earth history and trait innovation drive the global radiation of modern toads

The distributions of species radiations reflect environmental changes driven by both Earth history (geological processes) and the evolution of biological traits (critical to survival and adaptation), which profoundly drive biodiversity yet are rarely studied together. Modern toads (Bufonidae, Amphibia), an iconic radiation with global distribution and high phenotypic diversity, are an ideal group for exploring these dynamics. Using phylogenomic data from 124 species across six continents, we reconstruct their evolutionary history. Biogeographic analyses suggest modern toads originated in South America approximately 61 million years ago (Ma), later dispersing to Africa and Asia, thereby challenging hypotheses of dispersal via North America. Species diversification rates increased after leaving South America, linked to Cenozoic geological events and key innovations like toxic parotoid glands for predator defence. The emergence of parotoid glands coincided with the South American dispersal, promoting diversification and enabling toads to dominate both Old and New Worlds. In contrast, the evolution of other traits, despite being crucial to adaptation, did not promote species diversification (e.g. large body size) or were ambiguously associated with expansion into the Old World (e.g. developmental modes). These findings highlight the adaptability of modern toads and reveal the interplay between Earth's history and phenotypic innovation in shaping biodiversity.