Paleobiology: fossil true bug with remarkable claws

Amber from the Kachin region of Myanmar has preserved a wealth of fossils offering insights into the diversity of the Cretaceous fauna of a 100 million-year-old forest ecosystem. The site continues to yield previously unknown species.

LMU researchers have now discovered the fossil of a true bug (Heteroptera) with an unusual morphological feature for insects – large claws on its front legs which recall the grasping appendages of crabs. These so-called chelae, which function like pincers or forceps, are extremely rare in insects.

Claws reinvented

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“Previously, such chelae were known from only three insect groups. This fossil therefore represents the fourth known case of these structures evolving independently in insects,” explains Privatdozentin Carolin Haug, zoologist at LMU’s Faculty of Biology.

Working with her team and in collaboration with researchers from the University of Rostock and the University of Oulu in Finland, Haug used micro-computed tomography to examine the fossil and visualize all structures of its anatomy in 3D. The results have now been published in the journal Insects.

A quantitative morphological analysis of the shapes of over 2,000 chelae and similar grasping structures from various extinct and living species showed that the chelae of the fossil true bug differ markedly from the corresponding structures in other insect species. In fact, similarly structured chelae occur in somewhat more distantly related arthropods such as decapods (crabs, lobsters, shrimps, etc.) and tanaids.

Water bugs in K-pop pose

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Because of this distinctive feature, the researchers placed the fossil true bug in a new genus of its own and gave it the scientific name Carcinonepa libererrantes. The genus name combines the Latinized Greek word for “crab” (carcino-) with nepa, a reference to the group of true water bugs known as Nepomorpha.

“The species name libererrantes is a Latinization of the highly successful K-pop group Stray Kids,” explains Carolin Haug. “The name seemed fitting because the posture of the fossil’s chelae strongly resembles the group’s trademark pose. Stray Kids, I should add, is the favorite band of one of the paper’s authors, Fenja Haug.”

Based on its preserved morphological features, the researchers identified the new species Carcinonepa libererrantes as a representative of the true water bugs (Nepomorpha) within the true bugs (Heteroptera). Apart from the striking chelae on its front legs, its body structure shows similarities to living representatives of the group Gelastocoridae, commonly known as toad bugs, which are adapted to life as terrestrial predators.

“The morphology of C. libererrantes suggests that this species had a similar lifestyle,” observes Carolin Haug. “We can imagine it living in a Cretaceous forest, probably near the coast.” The prominent chelae on its front legs were most likely used for catching small insects.