Diversity of archostematan beetle larvae through time with new fossils

Archostemata is a species-poor group of beetles. However, the morphological diversity of the group is still not completely grasped since many ingroups are only known by the adult representatives. Micromalthus debilis is often the most discussed representative of this group in literature and stands as an example of a complex and unique life cycle. The rest of the known representatives do not have such specialised life cycles. However, in many groups, only the ecology of the adults is known and the few known larvae show specialisations of softwood-borers. Here we summarise the known larvae of Archostemata and report a new fossil from Eocene Baltic amber. The new specimen shows many morphological characters known from modern larvae of Archostemata (e.g., the broad head or the distinct posteromedian indentation of the head capsule) and is highly likely a larval representative of the group, and therefore, represents the first larva of Archostemata from the Eocene. We also study and discuss two additional unidentified fossil specimens with similar body outlines originating from Cretaceous Myanmar amber. Additionally, we analysed all the available specimens with quantitative methods, both fossil and modern, new and from literature.