The Onthophagus brevifrons species complex (Coleoptera: Scarabaeidae: Scarabaeinae: Onthophagini) consists of the five species: Onthophagus cavernicollis Howden and Cartwright, Onthophagus subtropicus Howden and Cartwright, Onthophagus brevifrons Horn, Onthophagus cuevensis Howden and Onthophagus moroni Zunino and Halffter, all of which are strictly associated with underground habitats (caves or burrows) and are consequently considered troglobites. Nevertheless, the biology of Onthophagus Latreille species reported from caves is lacking. In this study, four grottoes in the Cuetzalan region were explored: Trompa de Elefante, El Fósil and El Nido del Murciélago (which belong to the poorly explored Gruta de Atepolihui), and the Tasalolpan cave, in the search for dung beetles. Onthophagus moroni was collected inside El Nido del Murciélago and Tasalolpan cave, representing a new record for El Nido del Murciélago, since its presence was previously recorded inside the Tasalolpan cave in 1988. Adults of O. moroni were collected alive 70 m inside the Tasalolpan cave, under a latrine of Peters' climbing rat, Tylomys nudicaudus (Peters) (Rodentia: Cricetidae). We redescribe the species, discuss its biogeography and provide an updated dichotomous key to enable the identification of the constituent species in the O. brevifrons species complex.