Fossil beetle species described with astonishing physical characteristics

A beetle encased in amber, examined by Dagmara Żyła.© LIB, Żyła


The new genus and species Midinudon juvenis is not only smaller than modern rove beetles (Staphylinidae), but also has a feature that is normally observed in it’s larval stage. However, why does this species differ so much from the currently living species? Were there environmental influences that have affected their development up to today? In a recent study, researchers among LIB beetle expert Dagmara Żyła seek answers and describe the new genus and species from Cretaceous amber.

This is the oldest known case of paedomorphosis in adult rove beetles known to science. This means that the researchers discovered characteristic in the newly described species that we currently find in larvae. Due to the unusual combination of morphological features in Midinudon juvenis, the authors suspect that the species was affected by multiple evolutionary processes that led to a reduction in size and the development of paedomorphic characteristics on the head: a Y-shaped line that is usually absent in other species of adult rove beetles.

The authors suspect that various  processes, such as paleo-environmental conditions, could have influenced the size of the insect. “Some fossil rove beetles that we know of are not significantly smaller than their extant relatives. It is possible that the reduction in size within the lineage was necessary for survival under the environmental factors at that time. However, to test this hypothesis more accurately, we would need to conduct further studies,” says Dr Dagmara Żyła, Head of Section Coleoptera. Some Burmese amber insects are much smaller than their extant relatives, not only in beetles, but also in other orders such as Hymenoptera, Neuroptera, and Hemiptera. Higher temperatures in the mid-Cretaceous period could have influenced the size of insects.

In addition, the authors of the study consider whether the reduced size of some fossil beetle species is only specific to their lineage or rather a general process that affected the entire fauna. It is unclear what factors could have triggered this reduction in beetles during the Cretaceous period. Although their smaller size brings certain limitations, it also offers the animals the opportunity to conquer new ecological niches, adapt to special dietary habits, avoid predators, or even spread more effectively across the globe.

Alexandra Tokareva, Katarzyna Koszela, Vinicius S. Ferreira, Shûhei Yamamoto & Dagmara Żyła: The oldest case of paedomorphosis in rove beetles and description of a new genus of Paederinae from Cretaceous amber (Coleoptera: Staphylinidae), Scientific Reports: 

Dr Dagmara Żyła
Head of Section Coleoptera


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