New click beetle larvae from about 100 million years ago and possible niche differentiation of predatory larvae in the past

Reports of beetle larvae in amber are relatively rare, compared to the size of the group Coleoptera. Yet, to understand an ecosystem such larvae are quite important, due to their long interaction time with the environment, their enormous biomass, and their highly diverse morphologies coupled to myriads of ecological functions. We here report 16 new fossil beetle larvae of Elateridae, the group of click beetles, preserved in Cretaceous Kachin amber (Myanmar/Burma). The morphology of the new specimens stands out by the head having a prominent fronto-clypeus dorsally and the mouthparts forming a special maxillo-labial complex. The posterior end of the specimens bears paired projections and a prominent anal opening ventrally. The morphology of the larvae, especially of the toothed sickle-shaped mandibles, indicates a predatory lifestyle. We performed a quantitative comparison of the newly reported fossil beetle larvae and fossil and extant lacewing larvae using a shape analysis. The latter seem to have occurred in the same habitat and both appear to have been predatory. The lacewing larvae seem to have been quite dominating, possibly competing with the beetle larvae for resources. Our results indicate a morphological and also ecological differentiation between the two groups. This outcome shows how functions in a shared habitat can differ in animals of similar size. Furthermore, we discuss the functional aspects of mandibles and stylets (special mouthparts of lacewings) and compare them between the new fossil beetle larvae and the fossil larvae of lacewings.