Abstract <p>The Atlantic Forest is one of the most endangered ecosystems, with more than 90% of the original cover replaced by urban and agricultural areas. Although the contribution of deforestation to the loss of biodiversity is clear, the response of assemblages is complex and usually not linear. Dung beetles are among the most studied insects worldwide because of their diversity, broad geographical distribution, and role in ecosystem functioning. Dung beetles are sensitive to forest cover and defaunation processes due to their dependence on mammal dung. Here, we explored the role of landscape structure across different radius (120, 500 and 1000&#xa0;m) and mammal activity on the functional diversity of dung beetles in 87 forest fragments across an agricultural landscape of the Southern Atlantic Forest&#xa0;of Argentina. We obtained a total of 4479 dung beetles corresponding to 31 species while using camera traps, we recorded a total of 3,357 separate events, identifying at least 33 terrestrial mammals. Forest cover, connectivity, and complexity were higher across fragments. We observed only a small influence of landscape structure, mammal activity, and their interactions at small scales on the dung beetle functional diversity, particularly in the functional evenness and originality. Forest cover and connectivity were probably over the threshold of species extinction, explaining the low influence on dung beetle functional diversity. However, the dung beetle community was dominated by necrophagous species, probably because of a defaunation process affecting mainly coprophagous species.</p> Implications for insect conservation <p> Forest conservation is necessary for maintaining dung beetle assemblages. Moreover, the defaunation of those forests must be reversed to avoid functional adverse effects such as the loss of coprophagous species and the biotic homogenization processes.</p>