Possible fungus-eating cucujiformian beetle larvae with setiferous processes from Cretaceous and Miocene ambers

Beetle larvae represent important components of the modern-day fauna. This should have been the case in the past as well. Yet, fossil beetle larvae are rare, or at least are rare in the literature, as identifying a beetle larva to a narrower taxonomic group is very challenging. This is even more complicated if prominent features have evolved convergently in several lineages. Yet, even in such cases, an ecological interpretation of the fossils is possible if the convergent character is coupled to a specific life habit. For example, different, not closely related, beetle larvae that possess setiferous processes. We here report on three beetle larvae, one from Miocene Mexican and two from Cretaceous Kachin amber, Myanmar. These larvae possess setiferous processes, most similar to the processes of modern representatives of Cucujiformia, especially of the groups Endomychidae, Erotylidae, Cerylonidae and Coccinelidae. Considering the shape of the entire habitus, we see the most similarities between the new larvae and the modern larvae of Endomychidae. However, the new larvae and the larvae of modern representatives differ in certain aspects, most prominently in the body size. The fossils are smaller than their extant counterparts with setiferous processes. Hence the fossils could represent larvae of Endomychidae, but the case remains unclear. Despite this uncertainty, we suggest a lifestyle of the fossil larvae as fungus-eaters on rotting wood. This lifestyle is not only known from extant larvae of Endomychidae, but also from other larvae with similar processes.