A pterosaur with a wingspan that could reach nearly 2 meters may have flashed deep green and magenta in the sunlight. Scientists reported on May 10 at bioRxiv.org that at least one species of the flying reptiles was iridescent. The evidence comes from a fossil more than 120 million years old, found in northeast China.
The animal is Sinopterus dongi, a small pterosaur. The specimen had not been examined before, and its soft tissue is unusually well preserved. David Martill, a paleontologist at the University of Portsmouth in England who was not part of the work, said “soft tissue preservation at this level of fidelity is incredibly rare.”
What the microscope showed
Pterosaurs carried pycnofibers, small filaments of varying shapes and sizes, and many resemble the protofeathers of some dinosaurs. Earlier studies had found melanosomes, pigment-containing structures, inside them. That led paleontologists to picture colorful crests and other patterned body parts. Shimmering color is a new idea.
Iridescence appears when an object reflects different colors depending on the viewing angle. It has evolved repeatedly in insects, birds and even some plants, often through layered structures that scatter light and split it into many hues.
The team examined the fossil with scanning electron microscopy and other techniques. Inside the pycnofibers they found ordered, layered arrays of melanosomes, resembling the structures that produce iridescence in modern bird feathers. Computer simulations indicated the fibers probably produced deep greens and magentas.
“The same colors that you find in pigeons, starlings and a whole host of other birds,” Martill said. He added that the finding “will really give the paleoartists something to go on,” but also means researchers have to go back and analyze other things, such as soft tissues in fossil feathers and dinosaur skin.
Metabolism and display
The mix of melanosome types in these fibers matches what is found in warm-blooded birds and mammals. Steve Brusatte, a paleontologist at the University of Edinburgh who was not involved, said that suggests the pterosaurs had high metabolisms and complex ways of regulating body temperature. He called the discovery “one of the most intriguing and surprising fossil discoveries of the past few years.”
Birds use iridescent plumage in courtship, parading shiny feathers to attract mates, and the new finding suggests pterosaurs may have done something similar.
Brusatte said it also changes how he thinks about dinosaurs. “We often think that simple protofeathers in dinosaurs evolved for insulation, like hair did in mammals,” he said. “Now we must consider the possibility that even the simplest dinosaur feathers arose as display structures.”
