The first fossil of a bird, or a bird-dinosaur relative, the archaeopteryx, has fascinated scientists for 150 years since it was first discovered in a quarry in Germany. For all that time there has been a debate, was archaeopteryx, a bird or a dinosaur? Could it fly or were the wings, tipped with claws, helping it climb and glide?
Now scientists at Brown University in Providence, Rhode Island, have analyzed a single fossil feather from an archaeopteryx, and come to the conclusion that not only is it highly likely that it could fly, but the archaeopteryx, which was the size of a modern raven, was also as black as its distant descendent, the raven at home here in the northwest, sacred to the First Nations of British Columbia and sacred or honoured in other cultures around the world.
The archaeopteryx feather used in the study was discovered in a limestone deposit in Germany in 1861, a few years after the publication of Charles Darwin’s On the Origin of Species.
For most of that time, as paleontologists studied that feather fossil and other fossil specimens, popular science portrayed the archaeopteryx as the dinosaur at the base of the bird evolutionary tree. The traits that make archaeopteryx an evolutionary intermediate between dinosaurs and birds, scientists say, are the combination of reptilian features (teeth, clawed fingers, and a bony tail) and avian features (feathered wings and a wishbone).
The team examining the fossil feather not only determined that it was raven black but that the wing feathers were rigid and durable, traits that would have helped archaeopteryx fly.
The fact that archaeopteryx’s feather structure is identical to that of living birds, shows that modern wing feathers had evolved as early as 150 million years ago in the Jurassic period.
“If archaeopteryx was flapping or gliding, the presence of melanosomes [pigment-producing parts of a cell] would have given the feathers additional structural support,” said Ryan Carney, an evolutionary biologist at Brown and the paper’s lead author. “This would have been advantageous during this early evolutionary stage of dinosaur flight.”
Carney, with researchers from Yale University, the University of Akron, used a powerful scanning electron microscope at the Carl Zeiss laboratory in Germany to analyze the feather. They discovered that it is a “covert,” so named because these feathers cover the primary and secondary wing feathers birds use in flight.
They were were looking for melanosomes, the organelle in living organisms that contain melanin, which help determine colour.
Using the high powered electron microscope, the team located patches of hundreds of the structures still encased in the fossilized feather.
“We finally found the keys to unlocking the feather’s original colour, hidden in the rock for the past 150 million years,” said Carney, a graduate student in the Department of Ecology and Evolutionary Biology, studying with Stephen Gatesy.
Many artists’ conceptions over the years have shown archaeopteryx brightly coloured, often with brilliant blues like a tropical jungle bird today. Others show it with brownish camouflage like plumage.
The team measured the length and width of the sausage-shaped melanosomes, roughly 1 micron long and 250 nanometres wide. To determine the melanosome’s colour, Akron researchers Matthew Shawkey and Liliana D’Alba statistically compared Archaeopteryx’s melanosomes with those found in 87 species of living birds, representing four feather classes: black, gray, brown, and a type found in penguins. “What we found was that the feather was predicted to be black with 95 percent certainty,” Carney said.
Next, the team sought to better define the melanosomes’ structure. For that, they examined the fossilized barbules — tiny, rib-like appendages that overlap and interlock like zippers to give a feather rigidity and strength. The barbules and the alignment of melanosomes within them, Carney said, are identical to those found in modern birds.
What the pigment was used for is less clear. The black colour of the Archaeopteryx wing feather may have served to regulate body temperature, act as camouflage or be employed for display. But it could have been for flight, too.
“We can’t say it’s proof that Archaeopteryx was a flier. But what we can say is that in modern bird feathers, these melanosomes provide additional strength and resistance to abrasion from flight, which is why wing feathers and their tips are the most likely areas to be pigmented,” Carney said. “With Archaeopteryx, as with birds today, the melanosomes we found would have provided similar structural advantages, regardless of whether the pigmentation initially evolved for another purpose.”
The study, which appears in Nature Communications, was funded by the National Geographic Society and the U.S. Air Force Office of Scientific Research.