The New York Times, September 1, 2009Link
Birds, more than any other group of animals, are a celebration of color. They have evolved to every extreme of the spectrum, from the hot pink of flamingos to the shimmering blue of a peacock’s neck. Yet, for decades, paleontologists who study extinct birds have had to use their imaginations to see the colors in the fossils. Several feather fossils have been unearthed over the years, but they have always been assumed to be colorless vestiges.
Now a team of scientists has discovered color-producing molecules that have survived for 47 million years in the fossil of a feather. By analyzing those molecules, the researchers have shown that they would have given a bird the kind of dark, iridescent sheen found on starlings and other living birds.
This new method may allow scientists not only to reconstruct ancient birds more accurately. Birds evolved from ground-running feathered dinosaurs, and now it may be possible to determine some of the colors on them as well.
“I really do think we are moving from dinosaurs in black and white to dinosaurs in Technicolor,” said Julia Clarke, a University of Texas paleontologist who was a co-author of the new paper, published in the journal Biology Letters.
The new research got its start with squid. Jakob Vinther, a graduate student at Yale, was examining a fossil of a squid when he discovered that its ink sac was packed with microscopic spheres. They were identical to the pigment-loaded structures that give color to ink in living squid, known as melanosomes.
Knowing that birds make melanosomes in their feathers, Mr. Vinther decided to look for them in bird fossils. He knew that unlike the spherical melanosomes in squid, birds make sausage-shaped ones. “When I zoomed in on the fossils, it was nothing but these little sausages,” Mr. Vinther said.
But Mr. Vinther had to rule out the possibility that the sausages were bacteria that fed on the feathers after the birds died and then fossilized. He and his colleagues did that by examining an unusual fossil feather from Brazil with a pattern of dark and white stripes. Last year they reported that they found the sausage-shaped structures only in the dark stripes and none in the white ones. It is unlikely that the bacteria would grow in such an arbitrary pattern.
Mr. Vinther and his colleagues then decided to look for fossil melanosomes that still preserved clues to the colors of the birds in life. Melanosomes produce colors not just with the pigments they contain, but also with their organization inside the feather. In the case of some birds, for example, their feathers bounce some light off the outer surface while allowing some to penetrate and bounce off an inner layer of melanosomes. Depending on how the melanosomes are spaced, the two waves of light can interfere with each other in different ways, producing different colors.
To find well-preserved feathers, the scientists traveled this May to a famed fossil site in Germany near the village of Messel, where exquisitely preserved 47-million-year-old bird fossils are regularly dug up in an old quarry pit.
The scientists inspected several fossils and removed small pieces from 12 fossilized feathers. They returned home to put the material under a scanning electron microscope. “You can see a surface of beautifully packed together melanosomes,” said Richard Prum, a Yale expert on feather colors. “This looks exactly like a grackle or a starling, where you have a dark glossy bird with a metallic sheen.”
The scientists now plan to shift from isolated feathers to a complete bird fossil. “We can document its plumage over its entire body,” Dr. Prum said.
David Martill, a paleontologist at the University of Portsmouth who was not involved in the study, said the research was exciting. He is especially interested in how this method might be used to understand how birds evolved from feathered, flightless dinosaurs. Birds today use their range of colors and feather patterns to set themselves apart from other species and to attract mates. It is possible that dinosaurs evolved these colors before they evolved the ability to fly.
Dr. Clarke said she and her colleagues hoped to explore that question. “This is just a proof of concept that this kind of color can be preserved in the fossil record,” Dr. Clarke said, “but we’re not stopping there.”
Copyright 2009 The New York Times Company. Reprinted with permission.