Oldest feathered dino shows its colors

Finding suggests plumage first evolved for display, not flight

Another week, another colorful feathered dinosaur. Hot on the heels of a recent report identifying pigments in fossilized dino feathers and filaments (SN Online: 1/27/10), a different team of scientists says that it has mapped the full pattern of plumage sported by the oldest known feathered dinosaur.

SPEEDY RACER Microscopic analyses of fossilized feathers from Anchiornis huxleyi indicate that the dinosaur had striking, multicolored plumage. © 2010 National Geographic | Original image link: http://bit.ly/bsuElc

Paleontologists first described Anchiornis huxleyi, which lived in what is now northeastern China between 151 million and 161 million years ago, in September (SN: 10/24/09, p. 8). Reports of the lithe, peacock-sized dinosaur caused quite a stir, not least because the feathered creature was older than Archaeopteryx, which is considered by many scientists to be the oldest known bird.

Now, analyses of fossil feathers from all parts of A. huxleyi’s body — reported online February 4 and in an upcoming Science — provide a detailed look at the dino’s color scheme. The new findings also bolster the notion that feathers first evolved for a purpose other than flying, scientists say.

A. huxleyi had black and gray body plumage, the team’s investigations suggest. And while the long feathers on the front and side of the creature’s crest were gray, those sprouting from the top and back of its head were reddish-brown. Along with reddish-brown spots on its head and neck, A. huxleyi sported white racing stripes on its legs and its winglike forelimbs.

Paleobiologist Jakob Vinther of Yale University and his colleagues took a microscopic look at fossilized feathers at 29 sites on a specimen of A. huxleyi unearthed early last year. Some analyses focused on the small, simple feathers that covered the creature’s body and skull, and others targeted the longer, more complex feathers that adorned its forelimbs, legs and feet. “There was hardly any part of the creature that wasn’t feathered,” Vinther notes.

Almost all of the feathers the team scrutinized contained well-preserved remnants of pigment-bearing structures called melanosomes. Feathers lacking melanosomes were probably white, the researchers note. By comparing the size, shape, density and arrangement of melanosomes in each fossil feather with those in variously colored feathers of modern birds, the team then sketched out what A. huxleyi looked like. “Using those comparisons, we can reliably predict [the creature’s] color and map the whole animal,” Vinther says.

The team’s analyses “reveal an enormous array of information,” says Michael Benton, a paleontologist at the University of Bristol in England. The black-and-white bars on A. huxleyi’s forelimbs, as well as its colorful crest, are reminiscent of similar features in modern birds, he adds.

Knowing when color appeared in feathers or filaments may help solve the conundrum of why those structures evolved in the first place, Benton says. After all, he notes, A. huxleyi’s feathered forelimbs weren’t sufficiently large enough to carry the creature’s weight in flight. “What’s the function of half a wing?” he asks. The fact that feathers appear in the fossil record long before flight-capable birds suggests that feathers initially served a behavioral function, possibly one related to sending visual signals, and only later began to serve an aerodynamic function.

Philip J. Currie, a paleontologist at the University of Alberta in Edmonton, Canada, agrees: “Ancient creatures didn’t just sprout feathers and start flying. The feathers were there for another reason first.” Fossils reveal that dinosaurs often had very large eyes and sizable optic lobes in their brains. “Dinosaurs were very visual animals, just like birds are,” he adds.

Bold patterns of plumage, such as those seen in A. huxleyi, could have served any of a number of functions, Vinther and his colleagues speculate. Besides communicating to members of its own species — a “come here, cutie” to members of the opposite sex, say, or a “back off” message to rival suitors — a quick flash of boldly colored plumage could startle an attacking predator or flush prey out of hiding, the researchers say.

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