Fossils reveal relationship between feathered dinosaurs and beetles
Fossils in amber have revealed the long-term relationship between feathered dinosaurs and feather-feeding beetles
The amber fragments preserved the remains of feathers and larvae related to modern feather-feeding beetles in intimate contact and 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 new research.
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 the 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 that 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 time is thought to have critically shaped their evolutionary history, leading to co-evolution. 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.
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, said: “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.
“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, from the Botanical Institute of Barcelona (CSIC-Barcelona City Council) and co-author of the study, said: “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.”
The most impressive, complete specimen was found in the amber deposit of Rábago/El Soplao in northern Spain, roughly of the same age as San Just.
Dr Ricardo Pérez-de la Fuente, from Oxford University Museum of Natural History and co-lead author of the study, added: “It is unclear whether the feathered theropod host also benefitted from the beetle larvae feeding on its detached feathers in this plausible nest setting.
“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.”
The research is published in Proceedings of the National Academy of Sciences of the United States of America.
Image 1: Moult remains of feather-feeding beetle larvae intimately associated with downy feather portions from an unidentified theropod dinosaur in Early Cretaceous amber of Spain. Insets show the head with powerful mandibles of one of the larval moults (bottom) and the pigmentation pattern of feather second-order branches (top), with the main stem of one feather at the right of the amber fragment. Amber fragment is only six millimetres across.
Image 2: Isolated moult of the feather-feeding beetle larva found in the Spanish amber outcrop of Rábago/El Soplao, with detail of its powerful mandibles. Length of the moult is less than two millimetres.
Both images: © CN IGME-CSIC.