Aim: Southern Africa harbours a diverse array of dung beetles (Scarabaeidae: Scarabaeinae), with many species endemic to the region. Despite this diversity, the historical drivers of their evolution remain largely unexplored. This study investigates the evolutionary history of the flightless dung beetle genus Macroderes, testing its monophyly and assessing the role of environmental transitions in shaping its diversification. Location: Southwestern Africa, particularly the Greater Cape Floristic Region. Taxon: The dung beetle genus Macroderes (Scarabaeidae: Scarabaeinae). Methods: We conducted molecular phylogenetic analyses across multiple Macroderes species to test monophyly. Using BIOGeoBEARS, we inferred its ancestral range. To explore its biogeographical history and assess how late Cenozoic aridification in southwestern Africa shaped present-day microallopatric speciation patterns, we performed ancestral character reconstruction analyses. These examined Macroderes' origins, environmental adaptations (semi-arid vs. moist habitats), and the emergence of flightlessness as an adaptive trait, specifically investigating whether the genus descended from volant or flightless ancestors. Bayesian diversification models evaluated diversification dynamics. Results: Our findings support Macroderes' monophyly, with its most recent common ancestor (MRCA) originating in the late Miocene (similar to 8.44 mya; 95% CI: 9.74-7.06 mya). The MRCA was flightless and associated with a semi-arid environment resembling the present-day Succulent Karoo biome. Subsequent diversification involved multiple southward colonisation events into Fynbos, indicating repeated environmental transitions. Main Conclusions: The evolutionary history of Macroderes highlights how aridification and flightlessness have shaped its diversification. Flightlessness in Macroderes is closely linked to adaptation to semi-arid environments, restricting dispersal and contributing to the genus's short-range endemicity. Repeated southward movement highlights the dynamic evolutionary history of Macroderes and the significant role of environmental transitions in shaping its lineage. Our findings highlight the role of historical climatic changes in driving speciation within flightless dung beetles.