Amber fossils reveal dinosaurs and beetles had symbiotic relationship

Battered feathers and prehistoric beetle larvae encased in amber have revealed a relationship between dinosaurs and insects that stretches back more than 105 million years – the oldest example of symbiosis between dinosaurs and arthropods.

“Finding feather portions was already exciting,” says Ricardo Pérez-de la Fuente at the University of Oxford Museum of Natural History, but the discovery of the remains of beetle larvae among the feather fragments “was an incredible surprise”.

“Direct evidence of interactions between arthropods and vertebrates is exceedingly rare in the fossil record,” says Pérez-de la Fuente.

The amber was found in Spain and dates back to the Cretaceous period. The precise species of dinosaur the feathers belonged to is unclear, but the plumage matches what palaeontologists expect of theropod dinosaurs like Velociraptor and ancient birds.

At first, Pérez-de la Fuente and his colleagues couldn’t be sure that the association between the dinosaur feathers and beetle larvae was anything more than accidental as the tree sap that hardens into amber encases any material in its path.

On close examination, however, the researchers were able to pick out evidence that the beetle larvae were feeding on the dinosaur feathers. Inside the amber, the feathers weren’t pristine – they had been damaged and degraded before being enclosed. There were also faecal pellets created by the larvae among the feathers, says Pérez-de la Fuente.

While there are insects that live and feed on birds as parasites, says Pérez-de la Fuente, the story behind the Cretaceous dinosaur feathers and the larvae is different.

The larvae in the amber lack the critical features that would indicate they were living on the dinosaurs, such as specialised mouthparts for feeding on skin or blood, say the researchers. Instead, they suggest the beetle larvae were living and growing in the nest, making the most of what the dinosaurs shed. The researchers propose this as a case of a mutualistic relationship, with the larvae gaining a meal while also acting as a cleaning crew for the dinosaurs.

The insect larvae fossils appear to belong to a group of beetles with species alive today, say the researchers. Called dermestids, or skin beetles, some current species have larvae that live in bird nests and consume moulted feathers.

“The study presents fairly compelling evidence that Cretaceous-age dermestid beetles took advantage of that food source, especially since dermestids are found in present-day nests and areas where shed feathers accumulate,” says palaeontologist Lisa Buckley.

Ninon Robin at the Royal Belgian Institute of Natural Sciences says the finding unveils one of the “earliest dino-arthropod interactions, which are very hard to document in fossils”.