ABSTRACT Aim Island archipelagos and montane regions of East and Southeast Asia represent some of the world's most biodiverse yet poorly understood biogeographic systems. Whether regional diversity accumulates primarily through in situ speciation, dispersal‐mediated range shifts, or some combination of these processes remains unclear. Using Sinomicrurus coralsnakes as a model system, we aim to understand how geographic ranges have shifted over time, whether major biogeographic events align with geological and climatic transitions across Indochina and adjacent subtropical Asia, and whether dispersal involves tracking ancestral climatic niches or evolving new niche strategies. Location Indochina and adjacent subtropical Asia (southern China, Sino‐Japan, Taiwan, Ryukyu Archipelago, Himalayan foothills). Taxon Sinomicrurus coralsnakes (Serpentes: Elapidae). Methods We use time‐calibrated phylogenies, probabilistic ancestral‐range estimations with biogeographic stochastic mapping, species distribution models, and phylogenetic and statistical analyses of multivariate climatic niches to examine historical range shifts, the timing of major biogeographic events, and patterns of niche conservatism versus niche evolution in Sinomicrurus . Results Species distribution models revealed that precipitation‐related variables largely structure Sinomicrurus distributions, with temperature and elevation contributing secondarily. Niche analyses indicated clear ecological differentiation among species, with island endemics and highland taxa occupying the most distinct climatic positions. Divergence‐time estimates place the origin of crown Sinomicrurus in the mid‐Miocene, with major clades diversifying through the Miocene–Pliocene. Phylogenetic signal in climatic niche axes was absent. Biogeographic analyses under the best‐supported DIVALIKE+J model identified founder‐event dispersal as the dominant mechanism, while vicariance was inferred at low frequency. Main Conclusions Diversification in Sinomicrurus coincides with late Miocene to early Pliocene geological and climatic transitions, with episodic founder‐event dispersal repeatedly driving range shifts from a persistent Indochinese source into climatically distinct highland and island environments. Geographic dispersal predicts niche position better than phylogenetic relatedness, consistent with niche evolution contingent on colonisation rather than phylogenetic constraint. These findings highlight that founder‐event dispersal represents an underappreciated mechanism of biodiversity generation in East and Southeast Asia, complementing the vicariance and in situ speciation more commonly invoked for this region.
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