Sexual dimorphism in mid-Cretaceous silvanid beetles from northern Myanmar (Coleoptera, Silvanidae, Brontinae)

Silvanidae is a small group of cucujoid beetles, and their fossil record is poorly documented. The two recently described genera from Burmese amber, Cretoliota Liu et al. and Protoliota Liu et al. , are distinctive among all known Silvanidae, displaying markedly long antennae and mandibular horns in males, as found in the extant Uleiota Latreille. Due to the limited sampling of fossil specimens, the morphological variations of male mandibular horns remain a mystery. Here we report six well-preserved specimens of Protoliota with both male and female genitalia exposed from mid-Cretaceous Burmese amber. Our discovery confirms the presence of remarkable sexual dimorphism in Protoliota . Males of Protoliota antennatus Liu et al. display short to very long mandibular horns and much longer antennae. Interesting morphological convergence of the beetles (Silvanidae and Staphylinidae) living under the bark of dead trees is briefly discussed. Our discovery represents the first definitive sexual dimorphism in beetles from Burmese amber.