The evolution of the mouthpart structures in the Eucraniini (Coleoptera, Scarabaeidae)

The Eucraniini are a small dung beetle tribe endemic to Argentina (4 genera with 14 species), adapted to live in extremely arid environments, usually feeding on dry, small mammal dung pellets. These beetles grasp the dried pellets lifting them by the foretibiae and run forward on the middle and hindlegs. Here, the eucraniine mouthparts (epipharynx, labium, mandibles and maxillae) and ventral part of the clypeus were examined. According to the results, the structures were collectively defined as MOS (i.e., mouthpart structures), which is related to the unique feeding behavior displayed by these dung beetles (i.e., the food-lifting). The modification patterns of the MOS were examined in the lifters Eucraniini and compared to those of Neotropical tunneler species of Phanaeini and Dichotomiini, but also to the Afrotropical genus Pachysoma, with which they share many characters. Well-differentiated and distinguished MOS were detected in the three Neotropical tribes Eucraniini, Phanaeini, and Dichotomiini, evidencing also how the variation patterns of this complex system mirror the phylogenetic relationships among these tribes, and also within the Eucraniini genera.