The Onthophagus fuscus Boucomont, 1932 (Coleoptera: Scarabaeidae: Scarabaeinae: Onthophagini) species complex has a total of eight species, one of which is a new species (Onthophagus orizabensis new species) and three are elevated from the subspecies level (O. canescens Zunino Halffter, 1988 new rank; O. mycetorum Zunino Halffter, 1988 new rank; O. parafuscus Zunino Halffter, 2005 new rank). Onthophagus navarretorum Delgado Capistan, 1996 is included, while Onthophagus semiopacus has been removed from the species complex. The distribution map and key for the identification of species in this species complex are updated. Habitat preferences, ecological tolerance, and the restriction of this species complex to the mountains of the Mexican Transition Zone are discussed.
Keywords: Coleoptera, dung beetles, Mexican Transition Zone, Trans-Mexican Volcanic Belt, mountain entomofauna, megafauna, mycophagy, necrophagy, coevolution.