April 28, 2003

Feather Expert Takes Fresh Look
At Link Between Birds And Dinosaurs
By Sherry Fisher

The origin of birds has generated controversy for 150 years. Now, a UConn professor emeritus has added to the debate with an article he co-authored about the discovery of dinosaurs with feathers.

According to Alan Brush, professor emeritus of physiology and neurobiology, the recent finding of fossils of flightless feather-beari ng dinosaurs in northern China has spurred scientists to take a fresh look at the evolutionary link between birds and dinosaurs.

In a cover article published in Scientific American in March, Brush and a colleague, Richard O. Prum, a professor at the University of Kansas, shed light on the mystery of the origin of feathers, based in part on the evidence of the fossils from China.

They propose a developmental theory that feathers evolved through a series of transitional stages, each marked by an evolutionary novelty that was essential for the appearance of the next stage. Their theory bases its proposals on the understanding of how feathers develop, rather than on assumptions about how they might have been used, or about the animals from which they may have evolved.

For many years, the first known prehistoric bird, the Archaeopteryx, discovered during Darwin's lifetime, was considered to be the missing link between reptiles and birds, Brush says. "These fossils didn't offer any new insights on the evolution of feathers, because they look like the feathers of modern birds.

"We now know that feathers first appeared in a group of theropod dinosaurs and diversified into essentially modern structural variety within other lineages of theropods before the origin of birds," says the article.

The structures on the newly discovered fossils from China look exactly like natal down, Brush says.

"The consequence of these amazing fossil finds has been a simultaneous redefinition of what it means to be a bird and a reconsideration of the biology and life history of the theropod dinosaurs," the authors write. "Birds - the group that includes all species descended from the most common ancestor of Archaeopteryx and modern birds - used to be recognized as the flying, feathered vertebrates. Now we must acknowledge that birds are a group of the feathered theropod dinosaurs that evolved the capacity of powered flight.

"The new evidence from developmental biology is particularly damaging to the classical theory that feathers evolved from elongated scales," the authors say. The new evidence also "puts to rest the popular and enduring theory that feathers evolved primarily or originally for flight."

Brush, who lives in Mystic, was on the UConn faculty from 1965 to 1995. His research has focused on feather pigment and keratin biochemistry and the evolution of feathers.