To characterise their functional diversity and seasonal activity, dung beetles (Coleoptera: Scarabaeoidea) were collected with baited pitfall traps at three sites for three years on a native grassland in southern Alberta, Canada. The total collection of 125 820 beetles comprised 12 species of which eight were of European origin. For each combination of site and year, assemblages were dominated by two or three core species of European origin that represented 70–95% of total beetles and more than 75% of total biomass, but only 10–30% of species richness. Core species consistently included Onthophagus nuchicornis (Linnaeus) and occasionally Chilothorax distinctus (Müller) and Colobopterus erraticus (Linnaeus). Coexistence of these core species appears to be facilitated by differences in their size, seasonal activity, and life history traits.