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 ~
61 million years ago, 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 defense. 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.