The phylogenetic validity of Pachysoma MacLeay, 1821, is assessed. Cladistic analysis of 64 adult characters from 37 taxa comprising all Scarabaeini genera (except the monotypic Madateuchus Paulian, 1953) and two outgroup Canthonini genera, resulted in some currently recognised genera (i.e. Sceliages Westwood, 1837; Kheper Janssens, 1940; and Drepanopodus Janssens, 1940) being recognised as para phyletic. Pachysoma comprises a monophyletic clade of highly derived Scarabaeus Linnaeus, 1758. To further nomenclatural stability within the Scarabaeini, Pachysoma should best be considered a subgenus of an expanded genus Scarabaeus. Neopachysoma Ferreira, 1953; Mnematium MacLeay, 1821 and Neomnematium Janssens, 1938 are maintained as synonyms of Scarabaeus s.l. The unique biology of Pachysoma is interpreted as an adaptation to arid conditions, and is presumably derived from ball rolling and wet dung feeding. Aridification of the Namib Desert is postulated to have initiated the eVolution of Pachysoma from a Scarabaeus-like ancestor, while dune movement accounts for their current distribution. The evolutionary history of Pachysoma is discussed based on the phylogenetic analysis, and distributional and biological information. Keywords: Insects, Coleoptera, Scarabaeidae, Scarabaeinae, Scarabaeini, Afrotropical, Pachysoma, Neopachysoma, Mnematium, Neomenmatium, Scarabaeus, Kheper, Sceliages, Orepanopodus, Pachylomerus, cladistic, phylogeny, endemic, dung beetles, flightless, food preference, dry dung, detritus, psammophily, relocation strategy, systematic revision, biology, distribution.