Some pterosaurs may have boasted bold iridescence

Some fossilized filaments are giving Earth’s first flying vertebrates a shiny new makeover. 

At least one species of pterosaur shimmered in iridescent greens and magentas, scientists report May 10 at 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 of the past few years,” says paleontologist Steve Brusatte of the University of Edinburgh, who was not involved with the research. 

The new work focuses on a previously unexamined specimen of Sinopterus dongi, a small pterosaur whose wingspan could reach nearly 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 glimpse into how pterosaurs might have looked.

“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 with the work.

Prior research has found that pterosaurs had pigment-containing structures known as melanosomes in their pycnofibers — small filaments of different shapes and sizes, with many similar to protofeathers found in some dinosaurs. Those findings have long led paleontologists to envision pterosaurs with colorful patterns on their crests and other body parts. But the finding 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 scatter light and split it into myriad colors.

For the new study, researchers scrutinized the fossil’s microscopic structure using scanning electron microscopy and other techniques. They found that the pycnofibers contained ordered, layered arrays of melanosomes. These layers resemble the melanosome-bearing structures that produce iridescence in modern bird feathers. 

The diversity of melanosomes within these fibers matches that found in warm-blooded birds and mammals, suggesting these pterosaurs had high metabolisms and complex mechanisms to regulate their own body temperature, Brusatte says.

Using computer simulations, the researchers determined 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 says. “It will really give the paleoartists something to go on … but it also means that we have to go back and analyze other things,” like soft tissues seen in fossil feathers and dinosaur skin.

In birds, iridescent plumage is widely known for its role in courtship rituals. Birds will dance in idiosyncratic ways, parading around their shiny plumage in an attempt to entice mates. The discovery of iridescence in pterosaurs suggests they may have been doing something similar.

“We often think that simple protofeathers in dinosaurs evolved for insulation, like hair did in mammals,” says Brusatte. “Now we must consider the possibility that even the simplest dinosaur feathers arose as display structures.”