Fossils indicate the long-term interaction between feathered dinosaurs and feather-feeding bugs.

According to an article titled “Symbiosis between Cretaceous dinosaurs and feather-feeding beetles,” which was published in the Proceedings of the National Academy of Sciences today, new fossils in amber have revealed that beetles fed on the feathers of dinosaurs about 105 million years ago. This demonstrates a symbiotic relationship that was either one-sided or beneficial to both parties.

The vitally golden pieces considered, from the Spanish region of San Just (Teruel), contain larval sheds of little scarab hatchlings firmly encompassed by parts of wool feathers. As both types of theropod dinosaurs lived during the Early Cretaceous and shared frequently indistinguishable feather types, the feathers belonged to an unknown theropod dinosaur, either avian (a term referring to “birds” in a broad sense) or non-avian. However, since the group first appeared in the fossil record approximately 30 million years later, during the Late Cretaceous, the studied feathers did not belong to modern birds.

Ticks infest cattle, frogs catch insects with their acrobatic tongues, and some barnacles grow on the skin of whales. These are examples of modern ecosystems. These are only a couple of the different and complex biological connections among vertebrates and arthropods that have coincided for in excess of 500 million years. It is believed that the interactions between these two groups over extended periods of time significantly influenced their evolutionary histories, resulting in coevolution. However, relationships between arthropods and vertebrates are extremely uncommon in the fossil record.

“Three additional amber pieces were also studied, each containing an isolated beetle molt of a different maturity stage but assigned to the same species, allowing a better understanding of these minute insects than is usually possible in paleontology,”

Dr. David Peris, from the Botanical Institute of Barcelona (CSIC-Barcelona City Council).

Dermestids, or modern skin beetles, were found to be related to the larval molts that were preserved in the amber. Dermestid beetles are well-known pests of stored goods and dried museum collections. They eat organic materials like natural fibers that are hard for other organisms to break down. Dermestids, which typically live in the nests of birds and mammals where feathers, hair, or skin accumulate, also play an important role in the recycling of organic matter in the natural environment.

Separated shed of the quill taking care of the scarab hatchling tracked down in the Spanish golden outcrop of Rábago/El Soplao, with detail of its strong mandibles (left). The molt is shorter than two millimeters in length. Credit: CN IGME-CSIC.

“Some of the feather portions and other remains—including minute fossil feces, or coprolites—in our samples are in close contact with the molts attributed to dermestid beetles and show occasional damage or signs of decay.” CN IGME-CSIC “Dr. Enrique Pealver, from the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC) and lead author of the study, explains that this is hard evidence that the fossil beetles almost certainly fed on the feathers and that these were detached from their host.”

“The beetle larvae spent their time eating, peeing, and molting in accumulated feathers on or near a resin-producing tree, most likely in a nest. That association was accidentally captured and held for millions of years by a flow of resin.

“Three extra golden pieces, each containing a confined scarab shed of an alternate development stage yet relegated to similar species, were likewise contemplated, permitting a superior comprehension of these moment bugs than what is typically conceivable in fossil science,” says Dr. David Peris, from the Plant Organization of Barcelona (CSIC-Barcelona City Gathering) and co-creator of the review. In the northern part of Spain, in the amber deposit of Rábago/El Soplao, the most impressive and complete specimen, roughly of the same age as San Just, was discovered.

Dr. Ricardo Pérez-de la Fuente, co-lead author of the study and from the Oxford University Museum of Natural History, says, “It is unclear whether the feathered theropod host also benefited from the beetle larvae feeding on its detached feathers in this plausible nest setting.” However, our data indicate that the larvae did not consume living plumage and lacked defensive structures, unlike modern dermestids, which can irritate the skin of nest hosts and even kill them, so the activity of the larvae probably did not harm the theropod.”

More information: Peñalver, Enrique et al, Symbiosis between Cretaceous dinosaurs and feather-feeding beetles, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2217872120

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