Dinosaur fossil yields feathery structures

March 8, 2001 at 2:31 pm

The oldest known bird, Archaeopteryx lithographica, lived roughly 150 million years ago and had modern feathers. But no one knows what earlier feathers may have looked like.

Researchers found these branched, featherlike structures near the skull of a 124-million-year-old dinosaur. Xing Xu et al./Nature

“To have an incredibly new and complex thing suddenly arise with no known antecedents is tough to explain,” says Richard O. Prum, an ornithologist at the University of Kansas in Lawrence. Prum and his coworkers from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing now report they’ve found feather antecedents on the remains of Sinornithosaurus millenii, a 124-million-year-old raptor dinosaur from Liaoning, China.

Although the Sinornithosaurus fossil is younger than that of Archaeopteryx, the newly described structures could represent precursors that evolved into Archaeopteryx’s feathers, the team argues in the March 8 Nature. Both creatures may have emerged from a common ancestor that had rudimentary feathers.

In recent years, researchers have unearthed dinosaur remains that appear to be covered in a layer of “dinofuzz,” notes Lawrence Witmer, a paleontologist at Ohio University in Athens. But these wispy hairlike structures are so unlike modern feathers that skeptics have all but dismissed the possibility that the two could be related (SN: 10/26/96, p. 260; 6/27/98, p. 404).

The newly discovered structures, however, appear to be made up of multiple filaments. “The only thing that grows on the skin of any vertebrate that has multiple filaments is a feather,” says Prum. What’s more, some of the filaments found on Sinornithosaurus are bound into tufts, like down, he adds.

The researchers found fossils of the downy structures near the dinosaur’s skull. On other parts of the body, they found a different featherlike structure made up of multiple filaments attached along a central shaft. “This is the first view of what some primitive feathers may have looked like,” says Prum.

Some researchers hold that feathers and birds evolved together, but this new evidence suggests that feathers showed up in the ancestor of Sinornithosaurus long before there were flying birds. The feathers could have kept dinosaurs warm, Prum speculates.

Some researchers aren’t convinced. “All these so-called feathered dinosaurs are younger than the first real known birds,” points out Storrs L. Olson, an ornithologist at the National Museum of Natural History in Washington, D.C.

Witmer counters that animals in some lineages can retain the more primitive features of an ancestor. For example, although the duckbilled platypus is a mammal, it lays eggs, a trait predating mammals.

Olson also contends that the dinosaur structures that Prum calls feathers and down could just as well be hair. “They want to see feathers . . . so they see feathers,” Olson adds. “This is simply an exercise in wishful thinking.”

Witmer agrees that the classification of the structures is debatable. “We’re looking at stuff strewn about on a rock, and consequently a lot of it is open to interpretation,” he notes. Unfortunately, feathers typically decompose, so their fossils are rare. The evidence required to resolve questions about their origin is likely to remain elusive, Witmer adds.