Pterosaur melanosomes support signalling functions for early feathers

Abstract

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.

Triassic Revolution

“…Pterosaurs, the sister group of dinosaurs, also have dermal insulating structures commonly called pycnofibres. New evidence (Yang et al, 2019;Cincotta et al, 2022) shows these pycnofibres take a variety of forms, including branching and tufting structures as seen among dinosaurs and birds (Figures 5B,C), so these are presumably also feathers. However, even if researchers balk at calling pycnofibres feathers, it does not change the fact that insulating dermal structures appeared in the first dinosaurs and the first pterosaurs, and the shared ancestry of these two clades is dated to the Early or early Middle Triassic.…”

Escape behaviors in prey might have underlain the evolution of pennaceous plumage in predatory dinosaurs

“…Plumage color patterns in non-avian feathered dinosaurs might have played a role in many aspects of their life, including signaling function, thermoregulation, and crypsis 18,78,79 . Plumage coloration, such as the light and dark regions in the tail fan of Caudipteryx 5 , might have been used in display and communication (e.g., intersexual communication) 18,19,80,81 regardless of whether it was used for flush-pursuing or not. For example, some extant flush-pursuers, such as the Painted redstart (Myioborus pictus), use white patches in flushing the prey 82 as well as in territorial interactions (the display behavior is different from these two functions).…”

Escape behaviors in prey and the evolution of pennaceous plumage in dinosaurs

“…h HYPOTHESIS 10. Intraspecific displays 16,17,39,40 : Use of forelimb and tail feathers in visual displays; distinct color patch and/or ornament feather (e.g., elongated feather) benefits display function; high within-species differences (e.g., sexual dimorphism, ontogenetic variation) are expected.…”

“…However, plumage color patterns in non-avian feathered dinosaurs might have also played a role in many aspects of their life, including signaling function, thermoregulation, and crypsis 16,37,38 , just as it happens in the extant avian flush-pursuers who often use wing/tail displays in aggressive or antipredatory contexts. We hypothesize that plumage coloration, such as the light and dark regions in the tail fan of Caudipteryx 3 , might have been used in display and communication 16,17,39,40 regardless of whether it was used for flush-pursuing or not. Some extant flush-pursuers, such as the Painted redstart (Myioborus pictus), use white patches in flushing the prey 36,41 as well as in territorial interactions (the display behavior is different from these two functions).…”