A True Bug with a True but Unique Chela in 100 Million-Year-Old Amber †

Abstract

Grasping appendages in representatives of the group Insecta are usually of the sub-chelate (jackknifing) type. Only rarely do chelate appendages occur: Carcinothrips (Thysanoptera), Dryinidae (Hymenoptera), and Carcinocorini (Heteroptera). Here, we report a new find from about 100 million-year-old Kachin amber, representing, to our knowledge, the first case of a fossil of the group Insecta with a chelate type of appendage. This find is only the fourth case of an independent or convergent evolution of such a structure. A quantitative morphological comparison of over 2000 grasping structures reveals that the proximal part of the chela (in this case, the femur) has a unique shape in the fossil, unparalleled in the fossil and modern fauna. Moreover, some other new fossils reported do not possess such a shape. The mouthparts, forming a distinct beak, allow us to identify the new fossil with the distinct chela as a representative of Heteroptera. Its short beak, together with some other characteristics, indicates that it most likely is a representative of Nepomorpha. Many other details of the fossil are not well preserved, but the overall appearance shows similarities to extant and fossil representatives of Gelastocoridae, a group of terrestrial predators.