Microscopic structures in fossil suggest animal had colors that changed depending on viewing angle
Certain fossilized filaments give new life to Earth’s first flying vertebrates.
At least one species of pterosaur shimmering with iridescent greens and magentasthe scientists report May 10 on bioRxiv.org. The discovery reshapes what we know about the fearsome flying reptiles, hinting at heightened metabolisms and hidden courtship displays.
“This is one of the most intriguing and surprising fossil discoveries in recent years,” says paleontologist Steve Brusatte of the University of Edinburgh, who was not involved in the research.
The new work focuses on a specimen of Sinopterus dongia small pterosaur whose scale could reach almost 2 meters. Found in northeast China, the fossil is more than 120 million years old and shows evidence of extraordinary soft tissue preservation, offering an unusual insight into what pterosaurs looked like.
“Soft tissue preservation at this level of fidelity is incredibly rare,” says David Martill, a paleontologist at the University of Portsmouth in England who was not involved in the work.
Previous research has shown that pterosaurs had pigment-containing structures called melanosomes in their pycnofibers — small filaments of different shapes and sizes, many of which resemble the protofeathers found in some dinosaurs. These discoveries have long led paleontologists to imagine pterosaurs with colorful patterns on their crests and other parts of their bodies. But the discovery that they might be iridescent is something new.
Iridescence occurs when an object reflects different colors depending on the viewing angle, creating a kaleidoscopic spectacle. It has evolved many times in the natural world – in insects, birds and even some plants and fungi. In each case, the shimmer comes from layered structures that diffuse light and split it into a myriad of colors.
For the new study, the researchers examined the microscopic structure of the fossil using scanning electron microscopy and other techniques. They found that the pycnofibers contained ordered, overlapping rows of melanosomes. These layers resemble the melanosome-bearing structures that produce the iridescence of modern bird feathers.
The diversity of melanosomes within these fibers matches that found in warm-blooded birds and mammals, suggesting that these pterosaurs had high metabolisms and complex mechanisms for regulating their own body temperature, Brusatte says.
Using computer simulations, the researchers determined that the fibers likely produced deep greens and magentas—”the same colors found in pigeons, starlings, and a whole host of other birds,” Martill says. “It will really give paleoartists something to do…but it also means we have to go back and analyze other things,” like the soft tissues seen in fossil feathers and dinosaur skin.
In birds, iridescent plumage is widely known for its role in courtship rituals. The birds dance in a unique way, parading around their brilliant plumage in an attempt to attract mates. The discovery of iridescence in pterosaurs suggests they might have done something similar.
“We often think that simple proto-feathers in dinosaurs evolved for insulation, like hair in mammals,” says Brusatte. “We must now consider the possibility that even the simplest dinosaur feathers appeared as display structures.”