Fluffy structures trapped in thumbnail-sized bits of ancient amber may represent some of the earliest evolutionary experiments leading to feathers, according to a new study. These filaments of "dinofuzz" are so well preserved that they even provide hints of color, the researchers say.
The oldest bird, Archaeopteryx, lived in what is now Germany about 150 million years ago, and the oldest known feathered dinosaur, Anchiornis huxleyi, lived in northeastern China between 151 million and 161 million years ago. Both creatures had modern-style feathers, each of which had a central shaft; barbs, which made up the feather's vane; and substructures called barbules tipped with Velcro-like hooklets that held the barbs together to form a sturdy aerodynamic surface.
Structures believed to represent earlier stages of feather evolution, such as flexible, unbranched filaments—often called protofeathers but sometimes dubbed "dinofuzz"—have been found in fossils of dinosaurs that lived long after Archaeopteyrx and Anchiornis but had not been discerned in older fossils.
When Ryan McKellar, a paleontologist at the University of Alberta in Canada, and his colleagues searched through more than 4000 bits of amber in Canadian museum collections, they found 11 specimens that included remnants of feathers and protofeathers. The largely transparent chunks of amber—most of them smaller than 1 centimeter across—had been pulled from coal deposits laid down about 78 million or 79 million years ago, when the region, then near sea level, was a wetland covered with conifer forests.
Upon closer inspection, McKellar and his team noticed that some of the feathers resemble those found on modern birds, complete with barbs sporting tiny Velcro-like hooks that lock onto adjacent barbs to create a sturdy flight surface. Some of these fragments likely came from a flight-capable bird. Others contained structures that helped the feathers absorb water, similar to those found on modern-day waterfowl, which use water-soaked feathers to counteract their buoyancy when they dive beneath the surface to chase prey or to forage on a lake bottom. These feathers possibly came from an ancient waterfowl similar to modern-day grebes, the researchers suggest.
But some of the structures embedded in the amber don't resemble anything seen on any creature living today, the researchers report online today in Science. In one instance, the amber holds regularly spaced, hollow filaments, each of which is about 16 micrometers in diameter, about the size of the finest human hair. The filaments apparently have no cell walls, so they're not plant fibers or fungal threads, McKellar says. And they don't have features that look like small scales, as mammal hair does. "We don't absolutely know what they are, but we're pretty sure what they're not," he notes. They could be protofeathers, McKellar says, because they resemble the carbonized structures found in some Chinese fossils preserved in sediments, which despite exquisite preservation of soft tissues such as feathers often don't preserve small details.
Although some of the feathers and protofeathers appear nearly transparent, others are heavily pigmented and probably were, in life, a deep brown, dark gray, or black. Previous studies of fossils preserved in rock have used x-ray fluorescence techniques to discern the concentration of copper and other trace metals that bind to melanosomes, the pigment-bearing structures in feathers, thereby yielding insights into the overall color patterns of early birds such as Archaeopteryx and Confuciusornis, which lived about 125 million years ago.
McKellar and his colleagues "present an exciting and broad sample of feathers," says Richard Prum, an evolutionary ornithologist at Yale University. Although the evidence suggests the filamentary structures are protofeathers, he notes, the lack of any other remains in the amber—a distinctive bit of bone, say, or a shred of skin—leaves open the possibility that the structures aren't associated with dinosaurs at all. Indeed, he says, they could be something completely new that hasn't been preserved elsewhere in the fossil record.