Significance Approximately a quarter of all land mammals are currently threatened, mostly by human activities including habitat loss and harvesting. Here, we provide the first biological map of priority areas that captures all three dimensions of mammalian biodiversity: taxonomic, phylogenetic, and traits. We find limited overlap in priority regions across the three dimensions and with currently protected areas, indicating that conservation planning should consider multiple dimensions of biodiversity to maximize biodiversity conservation. Our complementarity-based prioritization provides a conservation solution that can be incorporated in future conservation planning efforts aimed at helping protect not only species but also evolutionary potential and ecosystem function.