Fossils reveal the long-term relationship between feathered dinosaurs and feather-feeding beetles

Newswise —

A recent study published in Proceedings of the National Academy of Sciences of the United States of America has unveiled new fossils preserved in amber that shed light on the diet of beetles from approximately 105 million years ago. These findings suggest a symbiotic relationship between beetles and dinosaurs, wherein the beetles fed on the feathers of the dinosaurs, resulting in either one-sided or mutual benefits for both species.

The recent research focused on amber fragments found in the San Just locality in Teruel, Spain. These fragments contained moults of small beetle larvae, which were closely associated with sections of downy feathers. The feathers were determined to have originated from a theropod dinosaur, but whether it belonged to an avian (bird) or non-avian species remains uncertain. This is because both types of theropods co-existed during the Early Cretaceous period and had similar feather types that are difficult to differentiate. However, it was determined that the studied feathers did not belong to modern birds, as they appeared in the fossil record approximately 30 million years later, during the Late Cretaceous period.

In contemporary ecosystems, we can observe a plethora of intricate ecological relationships between vertebrates and arthropods. For instance, ticks infest cattle, frogs capture insects with their acrobatic tongues, and barnacles grow on the skin of whales, to name just a few examples. These relationships have existed for over 500 million years, and are vital in shaping the evolutionary history of both groups through coevolution. However, despite their significance, evidence of arthropod-vertebrate relationships in the fossil record is exceedingly scarce.

The preserved larval moults found in the amber were identified as being related to modern dermestid beetles, also known as skin beetles. Dermestid beetles are notorious pests that infest stored products and dried museum collections, as they feed on organic materials that are resistant to decay, such as natural fibers. However, these beetles also serve a crucial role in the natural environment as they participate in the recycling of organic matter. They are commonly found inhabiting nests of birds and mammals, where accumulated feathers, hair, or skin provide a food source for them to thrive on. Thus, dermestid beetles have a complex ecological role that includes both detrimental and beneficial aspects, depending on their context and environment.

Dr. Enrique Peñalver, the lead author of the study and a researcher at the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC), explains that in their samples, some of the feather fragments and other remains, including coprolites or fossil feces, were found in close association with the dermestid beetle moults. These remains displayed occasional damage and signs of decay, providing concrete evidence that the fossil beetles had indeed fed on the feathers and that they were detached from their host. This discovery sheds light on the feeding behavior of the ancient dermestid beetles and provides valuable insights into the ecological relationships between beetles and dinosaurs over 100 million years ago.

“The beetle larvae lived −feeding, defecating, moulting− in accumulated feathers on or close to a resin-producing tree, probably in a nest setting. A flow of resin serendipitously captured that association and preserved it for millions of years.” 

Dr. David Peris, a co-author of the study and a researcher at the Botanical Institute of Barcelona (CSIC-Barcelona City Council), notes that three additional amber pieces were examined, each containing an isolated beetle moult of a different maturity stage, but attributed to the same species. These rare specimens provided a unique opportunity to gain a better understanding of these tiny insects, which is often challenging in the field of paleontology. Among these specimens, the most remarkable and complete one was discovered in the Rábago/El Soplao amber deposit in northern Spain, estimated to be of a similar age as the San Just locality. This find further contributes to our understanding of the ancient arthropod-vertebrate relationships preserved in amber fossils.

Dr. Ricardo Pérez-de la Fuente, co-lead author of the study and a researcher at the Oxford University Museum of Natural History, points out that it remains uncertain whether the feathered theropod host derived any benefit from the beetle larvae feeding on its detached feathers in a possible nest setting. However, the data gathered from the fossils indicate that the theropod was unlikely to have been harmed by the activity of the beetle larvae. The larvae did not feed on living plumage and lacked defensive structures that are present in modern dermestid beetles, which can cause irritation or even death to nest hosts. This suggests that the theropod and the beetle larvae may have had a mutualistic relationship in which both parties benefited, although further research is needed to fully understand the dynamics of this ancient ecological interaction.

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Notes 

• (*) The paper “Symbiosis between Cretaceous dinosaurs and feather-feeding beetles” is published as open access in the journal Proceedings of the National Academy of Sciences of the United States of America (=PNAS).

• The international and multidisciplinary team comprised researchers from the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC), the Botanical Institute of Barcelona (IBB-CSIC), the University of Barcelona and the Institute for Research on Biodiversity (IRBio), the Complutense University of Madrid, the ‘Parque de las Ciencias’ of Andalusia, the Autonomous University of Madrid, and the Royal Academy of Exact, Physical and Natural Sciences (Spain); the American Museum of Natural History and the Natural History Museum of Los Angeles County (United States of America); the Senckenberg Research Institute (Germany); and Oxford University Museum of Natural History (United Kingdom). 

• Funding bodies: the project CRE, funded by the Spanish AEI/FEDER, UE Grant CGL2017-84419, the project PGC2018-094034-B-C22 (MCIU/AEI/FEDER, UE), the project CGL2014-52163, funded by the Spanish Ministry of Economy, Industry, and Competitiveness, the Secretary of Universities and Research of the Government of Catalonia and European Social Fund (2021FI_B2 00003), and the Consejería de Industria, Turismo, Innovación, Transporte y Comercio of the Gobierno de Cantabria through the public enterprise EL SOPLAO S.L. 

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