specimen of Archaeopteryx: Paleontologists have long thought that
Archaeopteryx fossils, including this one discovered in Germany, placed
the dinosaur at the base of the bird evolutionary tree. (Credit: Museum
für Naturkunde Berlin)
ScienceDaily (Jan. 24, 2012)
— Since its discovery 150 years ago, scientists have puzzled over
whether the winged dinosaur Archaeopteryx represents the missing link in
birds' evolution to powered flight. Much of the debate has focused on
the iconic creature's wings and the mystery of whether -- and how well
-- it could fly.
Some secrets have been revealed by an international team of
researchers led by Brown University. Through a novel analytic approach,
the researchers have determined that a well-preserved feather on the
raven-sized dinosaur's wing was black. The color and parts of cells that
would have supplied pigment are evidence the wing feathers were rigid
and durable, traits that would have helped Archaeopteryx to fly.
The team also learned from its examination that Archaeopteryx's
feather structure is identical to that of living birds, a discovery that
shows modern wing feathers had evolved as early as 150 million years
ago in the Jurassic period. The study, which appears in Nature Communications, was funded by the National Geographic Society and the U.S. Air Force Office of Scientific Research.
"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
The Archaeopteryx feather 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.
Paleontologists have long been excited about the fossil and other
Archaeopteryx specimens, thinking they place 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 lack of knowledge of Archaeopteryx's feather structure and color
bedeviled scientists. Carney, with researchers from Yale University, the
University of Akron, and the Carl Zeiss laboratory in Germany, analyzed
the feather and discovered that it is a covert, so named because these
feathers cover the primary and secondary wing feathers birds use in
flight. After two unsuccessful attempts to image the melanosomes, the
group tried a more powerful type of scanning electron microscope at
Zeiss, where the group located patches of hundreds of the structures
still encased in the fossilized feather.
"The third time was the charm, and we finally found the keys to
unlocking the feather's original color, 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.
Melanosomes had long been known to be present in other fossil
feathers, but had been misidentified as bacteria. In 2006, coauthor
Jakob Vinther, then a graduate student at Yale, discovered melanin
preserved in the ink sac of a fossilized squid. "This made me think that
melanin could be fossilized in many other fossils such as feathers,"
said Vinther, now a postdoctoral researcher at the University of
Texas-Austin. "I realized that I had opened a whole new chapter of what
we can do to understand the nature of extinct feathered dinosaurs and
The team measured the length and width of the sausage-shaped
melanosomes, roughly 1 micron long and 250 nanometers wide. To determine
the melanosomes' color, Akron researchers Matthew Shawkey and Liliana
D'Alba statistically compared Archaeopteryx's melanosomes with those
found in 87 species of living birds, representing four 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
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 color 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
Contributing authors include Vinther, Shawkey, D'Alba, and Jörg Ackermann from Carl Zeiss. Story Source:
Ryan M. Carney, Jakob Vinther, Matthew D. Shawkey, Liliana D'Alba, Jörg Ackermann. New evidence on the colour and nature of the isolated Archaeopteryx feather. Nature Communications, 2012; 3: 637 DOI: 10.1038/ncomms1642
Brown University (2012, January 24). Winged dinosaur Archaeopteryx dressed for flight. ScienceDaily. Retrieved January 26, 2012, from http://www.sciencedaily.com/releases/2012/01/120124113036.htm