Elateriform beetle larvae preserved in about 100-million-year-old Kachin amber

Abstract

Beetle larvae show high diversity in forms and ecological roles. Beetle larvae are often roughly categorised into certain larval types, for example: campodeiform, onisciform, scarabeiform, or elateriform. Larvae of the latter type are virtually absent from the fossil record. Here, we report three amber pieces from Cretaceous Kachin amber, Myanmar (about 100 million years old) that together include nine elateriform beetle larvae. One of the amber pieces has a single specimen included. The specimen is interpreted as a larva of Elateridae, the group of click beetles, possibly of the ingroup Elaterinae; yet accessible details are limited. Eight specimens within the other two amber pieces show certain similarities with larvae of Elateridae, but show significant differences in the trunk end, which bears two lobes armed with hooks in these fossils. This very specific structure is well known in modern larvae of Ptilodactylidae (toed-winged beetles). Therefore, the fossils are interpreted as larvae of Ptilodactylidae. Both types of here reported elateriform larvae represent the first fossil record of larvae of their respective groups. It is well known that larval morphology does not evolve in concert with adult morphology, and a modern-type morphology of the one may precede that of the other. Hence, the new fossils are important indicators of the appearance of the modern larval morphologies of their respective lineages. We also briefly discuss the fossil record of larvae of Elateriformia (of which Elateridae and Ptilodactylidae are ingroups) in general.