In many places, mammals are considered the dominant granivores in arid ecosystems. However, in Australia, ants are described as the dominant seed consumers and mammals as insignificant consumers. Since European settlement, many native Australian species have become rare or extinct, their declines preceding any understanding of their role in vegetation dynamics. In arid areas, native mammal decline has coincided with vegetation change. Our research explores granivory by Australia’s declining mammal species. We used foraging tray experiments inside rewilded areas and in areas with depauperate mammal communities to compare granivory rates in these areas. In our foraging trays we placed either Acacia ligulata or Dodonaea viscosa seeds. Both of these are common shrub species. We found that native mammals such as hopping mice (Notomys alexis) and the burrowing bettong (Bettongia lesueur) were the dominant predators of Dodonaea viscosa, and are approximately equal predators with ants for Acacia ligulata. We show that now rare native mammals were once important seed predators in arid Australia. The decline of omnivorous mammals across Australia may have facilitated vegetation change. Rewilding of these mammals will restore lost ecological functions to arid Australia.