29 ene 2012
The winged dinosaur Archaeopteryx, which may represent the missing link in birds' evolution to powered flight, had at least some jet-black feathers, according to new research published today in Nature Communications.
Aside from creating more of a cool visual for this raven-sized animal, the discovery suggests that Archaeopteryx could fly, since the color and parts of cells that would have supplied the black pigment are evidence that the wing feathers were rigid and durable. These are traits that probably would have permitted flight. The research team, led by evolutionary biologist Ryan Carney of Brown University, made another important discovery. The feather structure of Archaeopteryx turns out to have been identical to that of living birds, providing strong evidence that wing feathers evolved as early as 150 million years ago during 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," Carney was quoted as saying in a press release. "This would have been advantageous during this early evolutionary stage of dinosaur flight."
Archaeopteryx has been at the center of debate between scientists, who squabble over whether the animal was a non-avian dinosaur or a bird. It could have even been an intermediary between the two.
As for the feather, it 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. Thinking of Darwin ... the traits that might makeArchaeopteryx an evolutionary intermediate between dinosaurs and birds are the combination of reptilian (teeth, clawed fingers and a bony tail) and avian (feathered wings and a wishbone) features. Carney and his team patiently used a scanning electron microscope to locate patches of hundreds of the pigment structures, the melanosomes, 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.
The scientists also examined fossilized barbules within the feather. These are 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 all identical to those found in modern birds.
The black coloration offers possible clues about the behavior of Archaeopteryx. Black can serve to regulate body temperature, act as camouflage, be employed for display and, again, support flight.
"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."
