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

New fossils in amber have revealed that beetles fed on the feathers of dinosaurs about 105 million years ago, showing a symbiotic relationship of one-sided or mutual benefit, according to an article published in Proceedings of the National Academy of Sciences of the United States of America today*. 

The main amber fragments studied, from the Spanish locality of San Just (Teruel), contain larval moults of small beetle larvae tightly surrounded by portions of downy feathers. The feathers belonged to an unknown theropod dinosaur, either avian (a term referring to “birds” in wide sense) or non-avian, as both types of theropods lived during the Early Cretaceous and shared often indistinguishable feather types. However, the studied feathers did not belong to modern birds since the group appeared about 30 million years later in the fossil record, during the Late Cretaceous. 

When looking at modern ecosystems, we see how ticks infest cattle, frogs capture insects with acrobatic tongues, or some barnacles grow on the skin of whales. These are just a few of the diverse and complex ecological relationships between vertebrates and arthropods, which have coexisted for more than 500 million years. The way that these two groups have interacted throughout deep time is thought to have critically shaped their evolutionary history, leading to coevolution. Nevertheless, evidence of arthropod-vertebrate relationships is extremely rare in the fossil record. 

The larval moults preserved in the amber were identified as related to modern skin beetles, or dermestids. Dermestid beetles are infamous pests of stored products or dried museum collections, feeding on organic materials that are hard for other organisms to decay such as natural fibres. However, dermestids also play a key role in the recycling of organic matter in the natural environment, commonly inhabiting nests of birds and mammals, where feathers, hair, or skin accumulate. 

“In our samples, some of the feather portions and other remains – including minute fossil faeces, or coprolites – are in intimate contact with the moults attributed to dermestid beetles and show occasional damage and/or signs of decay. This is hard evidence that the fossil beetles almost certainly fed on the feathers and that these were detached from its host,” explains Dr Enrique Peñalver, from the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC) and lead author of the study. 

“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.” 

“Three additional amber pieces each containing an isolated beetle moult of a different maturity stage but assigned to the same species were also studied, allowing a better understanding of these minute insects than what is usually possible in palaeontology,” says Dr David Peris, from the Botanical Institute of Barcelona (CSIC-Barcelona City Council) and co-author of the study. The most impressive, complete specimen was found in the amber deposit of Rábago/El Soplao in the northern Spain, roughly of the same age as San Just. 

“It is unclear whether the feathered theropod host also benefitted from the beetle larvae feeding on its detached feathers in this plausible nest setting,” says Dr Ricardo Pérez-de la Fuente, from Oxford University Museum of Natural History and co-lead author of the study. “However, the theropod was most likely unharmed by the activity of the larvae since our data show these did not feed on living plumage and lacked defensive structures which among modern dermestids can irritate the skin of nest hosts, even killing them.” 

** 

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). For accessing an embargoed copy of the original article, please refer to PNAS’ EurekAlert! press note at https://www.eurekalert.org/news-releases/985779 

• 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. 

For further information and images, please contact: 

Dr Enrique Peñalver 

Senior Researcher 

Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC) 

e.penalver@csic.es 

Dr David Peris 

Beatriu de Pinós Postdoctoral Researcher  

Botanical Institute of Barcelona 
david.peris@ibb.csic.es  

+34 650 069 697 

Dr Ricardo Pérez-de la Fuente   
Deputy Head of Research  
Oxford University Museum of Natural History   
ricardo.perez-de-lafuente@oum.ox.ac.uk 
+44 01865 272971  

Notes to editors   

About Oxford University Museum of Natural History   

Founded in 1860 as the centre for scientific study at the University of Oxford, the Museum of Natural History now holds the University’s internationally significant collections of entomological, geological and zoological specimens. Housed in a stunning Pre-Raphaelite-inspired example of neo-Gothic architecture, the Museum’s growing collections underpin a broad programme of natural environment research, teaching and public engagement.  

www.oumnh.ox.ac.uk  

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