Pterosaur melanosomes support signalling functions for early feathers

Remarkably well-preserved soft tissues in Mesozoic fossils have yielded substantial insights into the evolution of feathers¹. New evidence of branched feathers in pterosaurs suggests that feathers originated in the avemetatarsalian ancestor of pterosaurs and dinosaurs in the Early Triassic², but the homology of these pterosaur structures with feathers is controversial³,⁴. Reports of pterosaur feathers with homogeneous ovoid melanosome geometries²,⁵ suggest that they exhibited limited variation in colour, supporting hypotheses that early feathers functioned primarily in thermoregulation⁶. Here we report the presence of diverse melanosome geometries in the skin and simple and branched feathers of a tapejarid pterosaur from the Early Cretaceous found in Brazil. The melanosomes form distinct populations in different feather types and the skin, a feature previously known only in theropod dinosaurs, including birds. These tissue-specific melanosome geometries in pterosaurs indicate that manipulation of feather colour-and thus functions of feathers in visual communication-has deep evolutionary origins. These features show that genetic regulation of melanosome chemistry and shape⁷⁻⁹ was active early in feather evolution.