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USC Unravels Feather Formation

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Scientists from the Keck School of Medicine of USC for the first time
have shown experimentally the steps in the origin and development of
feathers, using the techniques of molecular biology.

Their findings will have implications for the study of the morphogenesis
of various epithelial organs  from hairs to lung tissue to mammary glands
and is already shedding light on the controversy over the evolution of
dinosaur scales into avian feathers.

"The Morphogenesis of Feathers," a paper describing this work by principal
investigator and Keck School pathology professor Cheng-Ming Chuong and his
colleagues, was selected for online publication in the journal Nature.
The question of what makes a feather a feather has become rather heated in
the recent past, with the discovery in China in the 1990s of fossilized
dinosaurs like the Sinorthosaurus (Chinese-bird-dinosaur), with branching
skin appendages on its skin.

"Some say these things are feathers, some say they're protofeathers,
others say they're not feathers at all," Chuong said. "Everybody wants to
know which one is the real first feather."

And they also want to know how it came to be. Over the years, Chuong said,
paleontologists trying to trace the evolutionary connection between
dinosaurs and birds have looked at the ways in which a reptilian scale
might turn into an avian feather.
The standing hypothesis among many paleontologists has long been that the
scales on dinosaurs must have lengthened into rachides that then became
notched to form barbs and barbules. 

But there has been no real molecular evidence to either back up or refute
that argument until now.

In their Nature paper, Chuong and his colleagues have demonstrated how
barbs and rachides are formed in a modern chicken. They also have shown
that the evolution from scale to feather most likely followed a path in
which the barbs form first and then fuse to produce a rachis  rather than
a rachis forming first and then being sculpted into barbs and barbules.