Evolutionary stasis in enigmatic jacobsoniid beetles

Abstract

Jacobsoniidae is a small but perplexing beetle family, with unknown phylogenetic relationships to other polyphagan Coleoptera. To date, only a single fossil jacobsoniid has been described, from Eocene Baltic amber (~ 40 Ma). Here, we push back the oldest definitive record of Jacobsoniidae by approximately 60 million years with a new fossil species recovered from mid-Cretaceous (~ 99 Ma) Burmese amber from Myanmar. Remarkably, exploration of the fossil's morphology with confocal laser scanning microscopy revealed that it belongs to an extant genus, Derolathrus. The similarity of the new taxon, Derolathrus abyssus n. sp., to modern congeners provides a striking example of morphological stability over deep evolutionary time—a possible outcome of long-term persistence of mesic microhabitats, a hypothesis we argue is supported by a variety of other Recent, litter-inhabiting arthropod taxa now known to be largely unchanged since the Mesozoic. Many such examples belong to the Staphylinoidea—a hyperdiverse beetle superfamily that dominates contemporary mesic habitats, and with which Jacobsoniidae may have a close phylogenetic relationship.

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