Symbiosis between Cretaceous dinosaurs and feather-feeding beetles

Extant terrestrial vertebrates, including birds, have a panoply of symbiotic relationships with many insects and arachnids, such as parasitism or mutualism. Yet, identifying arthropod-vertebrate symbioses in the fossil record has been based largely on indirect evidence; findings of direct association between arthropod guests and dinosaur host remains are exceedingly scarce. Here, we present direct and indirect evidence demonstrating that beetle larvae fed on feathers from an undetermined theropod host (avian or nonavian) 105 million y ago. An exceptional amber assemblage is reported of larval molts (exuviae) intimately associated with plumulaceous feather and other remains, as well as three additional amber pieces preserving isolated conspecific exuviae. Samples were found in the roughly coeval Spanish amber deposits of El Soplao, San Just, and Penacerrada I. Integration of the morphological, systematic, and taphonomic data shows that the beetle larval exuviae, belonging to three developmental stages, are most consistent with skin/hide beetles (family Dermestidae), an ecologically important group with extant keratophagous species that commonly inhabit bird and mammal nests. These findings show that a symbiotic relationship involving keratophagy comparable to that of beetles and birds in current ecosystems existed between their Early Cretaceous relatives.

Automated summary

Extant terrestrial vertebrates, including birds, have symbiotic relationships with insects and arachnids, but arthropod-vertebrate symbioses in the fossil record are rarely found. In this study, direct and indirect evidence of beetles feeding on feather remains from an undetermined theropod host 105 million years ago is presented. An exceptional amber assemblage was found, including beetle larval exuviae associated with feathers, along with additional amber pieces containing isolated larval exuviae. The morphological and taphonomic data suggest that these beetle larval exuviae belonged to a keratophagous species, indicating a symbiotic relationship between beetles and their Early Cretaceous relatives similar to current ecosystems.