Sources and sinks: Geoclimatic dynamics shaped the assembly of endemic fauna in the world's Third Pole

The Qinghai-Tibet Plateau (QTP), a biodiversity hotspot shaped by tectonic and climatic forces, has seen significant progress in understanding its floristic origins. However, a comprehensive, multitaxon perspective on how its terrestrial fauna assembled remains lacking. Here we integrate time-calibrated phylogenies of over 20,000 species from five major groups (invertebrates, amphibians, reptiles, birds, and mammals), to reconstruct the evolutionary history of 527 terrestrial animal species endemic to the QTP. Our finding reveals that the QTP has functioned both as a center of in situ diversification and as a "biogeographic sink" that receives species from surrounding regions, however, with pronounced subregional differentiation: the Hengduan Mountains acted primarily as a diversification source, while the Himalaya and the Plateau Platform acted as sinks, accumulating lineages from adjacent regions. The Eocene-Oligocene climatic transition, rather than late Neogene uplift, initiated sustained faunal diversification and biotic exchange. Across subregions, distinct uplift histories and monsoon regimes drove asynchronous evolutionary trajectories, showing that even geographically adjacent regions can exhibit distinct accumulation patterns of lineages. Notably, integrating our faunal evidence with recent floristic assembly data reveals a consistent "plants first, animals later" pattern across the QTP and its subregions, suggesting that early-arriving plant lineages created ecological niches that facilitated subsequent faunal colonization and diversification. This framework advances our understanding of how mountain biotas assemble over time, with implications extending far beyond the QTP.