A team of researchers has discovered that plumage of Microraptor, a pigeon-sized dinosaur that lived about 120 million years ago, was iridescent with a glossy sheen like the feathers of a modern crow.
Artist's rendering of Microraptor in its ancient habitat (Jason Brougham / UT-Austin)
The discovery, published in the journal Science, shows that the tail feathering of Microraptor was ornamental, and likely evolved for courtship and other social interactions.
“Most aspects of early dinosaur feathering continue to be interpreted as fundamentally aerodynamic, optimized for some aspect of aerial locomotion,” said Dr. Julia Clarke, a co-author of the paper and a paleontologist at the University of Texas at Austin (UT-Austin). “Some of these structures were clearly ancestral characteristics that arose for other functions and stuck around, while others may be linked to display behaviors or signaling of mate quality.”
“Feather features were shaped by early locomotor styles”, the paleontologist explained. “But, as any birder will tell you, feather colors and shapes may also be tied with complex behavioral repertoires and, if anything, may be costly in terms of aerodynamics.”
The feather color displayed by many modern birds is partially produced by arrays of pigment-bearing organelles called melanosomes, about a hundred of which can fit across a human hair.
Generally found in a round or cigar-like shape, a melanosome’s structure is constant for a given color. Iridescence arises when narrow melanosomes are organized in stacked layers.
After a breakthrough by Dr. Jakob Vinther of UT-Austin in 2009, paleontologists started analyzing the shape of melanosomes in well-preserved fossilized feather imprints.
By comparing these patterns to those in living birds, scientists can infer the color of dinosaurs that lived many millions of years ago.
“Modern birds use feathers for many different things, ranging from flight to thermoregulation to mate-attracting displays,” said Dr. Matt Shawkey, a paper co-author and a biologist at the University of Akron. “Iridescence is widespread in modern birds, and is frequently used in displays. The evidence that Microraptor was largely iridescent suggests that feathers were important for display even relatively early in their evolution.”
Based on the new data from Microraptor and other findings, a complex color repertoire that includes iridescence is likely ancestral to a group of dinosaurs called Paraves that originated at least 140 million years ago. It includes dinosaurs like Velociraptor as well as Archaeopteryx, Anchiornis and living birds.
“This study gives us an unprecedented glimpse of what this animal (Microraptor) looked like when it was alive,” concluded Dr. Mark Norell, a paper co-author and a paleontologist at the American Museum of Natural History.
