A 100-million-year-old ensiferan with unusual mouthparts and comments on the evolution of raptorial appendages within Polyneoptera

Abstract

ABSTRACT Myanmar amber is known to provide fossils of the group Insecta with surprising morphologies. Here we present fossils of the new species Gryllobencain patrickmuelleri n. gen., n. sp. from Myanmar amber that possess an overall “orthopteroid” morphology, hence resemble crickets. Unlike in most crickets, thorax appendages 1 and 2 (“legs”) are large and prominent, even in comparison to thorax appendage 3. Furthermore, thorax appendages 1 and 2 are able to fold against themselves and are armed with prominent spine-like setae, indicating that these legs were originally used for grasping prey. Most prominent is a large spine on the tibia of both appendages distantly reminding of the tibial spur or claw of praying mantises. Comparable prey-catching apparatuses have evolved repeatedly in the group Polyneoptera: gladiators (Mantophasmatodea), three ingroups of bush-crickets (Saginae, Austrosaginae, Listroscelidinae) as well as one species of fossil mantises (Santanmantis axelrodi Grimaldi, 2003) appear to have used thorax appendages 1 and 2 for prey catching. The new fossils do not seem to be closely related to any of these groups. They differ especially by prominent cerci equipped with numerous, probably mechano-sensorial setae. In the other five groups, the cerci are significantly smaller, often indistinct. The fossils furthermore have prominent maxillae with sickle-shaped proximal parts and well-armed large palps, indicating that the maxillae played an important role in processing the prey. While the thorax appendages hence represent a case of clear convergent evolution, the uniqueness of the feeding apparatus leads us to recognise the fossils as a highly specialised new species.