Maintaining key ecological processes is a strong argument for conserving biodiversity, and this should extend to preventing the local extinction of keystone species that are otherwise common. Seed dispersal is such a process and chacma baboons (Papio ursinus ursinus) may facilitate seed dispersal, but currently suffer range contractions in South Africa. Between April 2016 and February 2017, we collected a total of 122 chacma baboon scat samples in a semi-arid subtropical thicket, South Africa, and identified food items and seeds from the scats. We show that chacma baboons are omnivores, able to disperse at least 24 different seed species. This is a wider range of seed species than those dispersed by a broad range of birds, reptiles or other mammals in subtropical thicket, and nearly five times that dispersed by domestic goats (Capra hircus). This suggests that baboons are key seed dispersers, whose role might not be substituted by goats. We believe that baboons may become more important seed dispersers in arid subtropical thicket as climate change alters the distributional ranges of plant communities. This important role as endo-zoochores highlights the need to conserve, rather than persecute, chacma baboons.