Feather Cells Tell of Microraptor's Crowlike Sheen M. Ellison/AMNH The fossilized Microraptor specimen from the Beijing Museum of Natural History. Sexual drive, not flight, may have been the main reason for the feather color and pattern of Microraptor, a four-winged dinosaur that lived some 130 million years ago in what is now northeastern China. New research by American and Chinese scientists shows that the animal had a predominantly glossy iridescent sheen in hues of black and blue, like a crow. This the earliest known evidence of iridescent color in feathers. The animal also had a striking pair of long, narrow tail feathers, perhaps to call attention to itself in courtship. In the study, published online Thursday in the journal Science, the researchers compared the patterns of pigment-containing cells from a Microraptor fossil with those of modern birds. The shape and orientation of these cells, known as melanosomes, were narrow and arranged in a distinctive pattern, as in the case of living birds with glossy feathers. Only recently has it become possible with scanning electron microscopes to examine well-preserved fossil remains of melanosomes, so tiny that a hundred can fit across a human hair. Such pigment agents in many birds are generally round or cigar-shaped, but these were especially narrow, like those of blackbirds. The iridescence arises when the melanosomes are organized in stacked layers. Matthew D. Shawkey, a biologist at the University of Akron in Ohio who conducted some of the most telling analysis of the melanosome-iridescence relationship, noted that modern birds use their feathers for many different things, including flight, regulation of body temperature and mate-attracting displays. Hypotheses concerning the function of iridescent colors in birds have centered on their role as visual social signals. "Iridescence is widespread in modern birds, and is frequently used in displays," Dr. Shawkey said in a statement. Our evidence that Microraptor was largely iridescent thus suggests that feathers were important for display even relatively early in their evolution. In the journal article, Uuanguo Li of the Beijing Museum of Natural History and his team drew the cautiously worded conclusion that "although we cannot assign a definitive function to iridescence in Microraptors, a role in signaling aligns with data on the plumage" of the specimen discovered in 2003. Eight other specimens were also examined in describing the likely role of their tail feathers in the mating game, like a peacock's today. A year ago, Canadian paleontologists described some of the first examples of feather coloring in the age of dinosaurs. They were found in 70-million-year-old amber preserving 11 specimens with a wide variety of feather types, some in bright colors. A different pigmentation method produces the brighter-colored features of, say, cardinals. Mark A. Norell, a dinosaur paleontologist at the American Museum of Natural History in New York, said the findings give "an unprecedented glimpse of what this animal looked like when it was alive." One result, he added, was to contradict previous interpretations that Microraptor was a nocturnal creature; dark glossy plumage is not a trait found in modern nighttime birds. Though its anatomy is similar to that of birds, and some dinosaurs are considered ancestral to living birds, Dr. Norell said, Microraptor is thought to be a non-avian dinosaur in a group called dromaeosaurs that include Velociraptor. The size of a large pigeon, Microraptor had two sets of wings, one on its arms and the other on its legs. Dr. Norell doubted that Microraptor could fly like living birds. Perhaps it could glide between trees or parachute to the ground, but it was more primitive than Archaeopteryx, often considered the early bird, and not capable of true powered flight. Julia A. Clarke, a paleontologist at the University of Texas at Austin and a member of the research team, noted that many experts continue to interpret dinosaur feathering in aerodynamic terms, and so it probably was to some extent. "But as any birder will tell you," Dr. Clarke said, "feather colors and shapes may also be tied with complex behavioral repertoires and, if anything, may be costly in terms of aerodynamics."