What color was that dinosaur? Posted: Wednesday, July 09, 2008 3:00 PM by Alan Boyle
Jacob Vinther / Yale
These images compare structures in a striped fossil feather (left side) and a
woodpecker feather (right side). Under the scanning electron microscope there are
melanosomes in the dark but not the light areas of the fossil (far left arrows). The
corresponding areas are shown at far right. Click on the image for a close-up.
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If dinosaurs had feathers, what did their plumage look like? Some artists have gone wild with their palette, decking out their dinos with parakeet pigments. But now there might actually be a way to figure out a dinosaur's true colors, thanks to a new technique for analyzing fossilized feathers.
The technique, pioneered by Yale researchers, involves looking at fossils with a scanning electron microscope for tiny structures that appear to be pigment-producing melanosomes. For years, it was thought that the imprints in the rock were fossilized bacteria, but in the journal Biology Letters, the researchers report that the spots are almost certainly melanosomes.
It makes sense that ancient creatures with feathers would have the same type of pigment-producing organelles that modern-day birds have, said Yale doctoral student Jacob Vinther, who conducted the research with paleontologist Derek Briggs and ornithologist Richard Prum.
"Birds frequently have spectacularly colored plumage, which are often used in camouflage and courtship display," Vinther said in a Yale news release. "Feather melanin is responsible for rusty-red to jet-black colors, and a regular ordering of melanin even produces glossy iridescence. Understanding these organic remains in fossil feathers also demonstrates that melanin can resist decay for millions of years."
The fossilized samples included a feather found in 100 million-year-old rocks from Brazil, and a 55 million-year-old bird skull from Denmark. The comparisons were made with a feather from a red-winged blackbird as well as with the retina of a whippoorwill, using a scanning electron microscope and an X-ray analyzer.
The imprints on both of the fossils matched up incredibly well with the modern melanosomes, which are found in the eyes and the skin as well as in the feathers. Melanin is also the coloring agent for mammalian fur - and your own hair, for that matter.
Could the 100 million-year-old fossilized feather have come from a dinosaur?
"In principle, it could be a dinosaur," Vinther told me. "We don't know. The [Brazilian rock] formation hasn't yielded any dinosaurs. They've discovered a few birds there. The most conservative answer, if you had to give one, is that it might be a bird."
msnbc.com file
This artist's conception shows what a feather-bearing
dinosaur known as Caudipteryx zoui may (or may
not) have looked like.
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The larger point is that the technique could be used in the future with dinosaur feather fossils. Prum came right out and said it in the news release: "Scientists have a way to reliably predict, for example, the original colors of feathered dinosaurs."
OK, suppose we find melanosomes in dino feathers. That would indicate that the feathers bore patterns of colors - but how could you determine which colors they were?
Vinther explained that different types of melanin are produced by differently shaped melanosomes. The sausage-shaped structures found in the fossilized feather from Brazil would have produced shades of black, using eumelanin. Round-shaped melanosomes produce reddish colors, using phaeomelanin.
The shading depends on how concentrated the melanosomes were. For round melanosomes, the palette ranges from that rusty red to lighter shades of brown, and then blond. For the sausage-shaped type, you're looking at blacks and grays.
"If the alignment of the melanosomes is really organized, and with a distinct spacing, that can give rise to diffraction," Vinther told me. That could produce a hummingbird's shimmery look, and even exotic shades of blue and green.
Melanin isn't the only factor behind coloration, as this explanation from the Cornell Lab of Ornithology makes clear. "Definitely you can start getting some idea of the coloration of birds, but this is something that needs to be studied further," Vinther said.
And we're not just talking about the feathers of birds and dinosaurs. Theoretically, other fossil features could be analyzed for their true colors. Researchers have reported finding fossilized skin from a 200 million-year-old ichthyosaur, and Vinther said a close analysis of the tissue could colorize our current picture of those ancient deep-sea monsters.
"You could see the organic imprints, and they look like the cells that would have the melanin inside," Vinther said.
http://cosmiclog.msnbc.msn.com/archive/2008/07/09/1189634.aspx
