Iridescence in pterosaur pycnofibers and the evolution of integumentary coloration

Abstract

The bodies of pterosaurs, the first flying vertebrates, are covered with integumentary filaments (pycnofibres) thought to be homologous to feathers in dinosaurs, but their coloration remains unknown. Here, we report a layered internal arrangement of melanosomes containing a photonic nanostructure within the monofilaments in a previously undescribed specimen of tapejarid pterosaur Sinopterus dongi from the Early Cretaceous Jehol Biota. Optical simulations showed that this structure reflects green to magenta iridescent coloration, confirming the presence of melanosome-based iridescent coloration previously thought to be unique to birds. This finding deepens our understanding of structure/color gamut relationships in amniotes, while supporting further shared characteristics associated with derived genetic and regulatory shifts in archosaurs.