Among beetles, thousands of species develop horns, the size of which is often extraordinarily disproportionate with respect to body size. The Scarabaeidae is the family in which horned species are most predominant, but other families, such as the Geotrupidae (dor beetles), also show remarkable horns, although in a more limited number of species. Horn expression mechanisms are well documented in Scarabaeidae but, despite the wealth of studies on this family, the horn morphological pattern of the Geotrupidae, to our knowledge, has never been investigated. In this paper, we describe for the first time the horn expression pattern in a dor beetle. As a study species, we chose Ceratophyus rossii, an Italian endemic dor beetle of the protected Mediterranean maquis in Tuscany, which shows remarkable head and pronotal horns in males and a notable cephalic horn in females. We identified and modeled shape and size horn patterns combining traditional and geometric morphometric approaches. We discuss the results in the wider landscape of developmental models described for other, more well-characterized, scarab beetles.