With the existence of feathered dinosaurs now being well established, a couple of researchers have moved on to learning more about how the feathers grew during the dinosaurs' lifetimes. By looking at samples of older and younger oviraptosaurs, they've noticed that that, unlike modern birds that grow normal feathers once their downy feathers molt away, the oviraptosaurs seem to have gone through multiple stages of feather development.

The work is based on two specimens—one oviraptosaur that had died and been fossilized in its youth, and another that had matured and lived longer. Both of the fossils had evidence of feathers on different areas of their body, but were nowhere near as fully feathered as creatures like the archaeopteryx.

Both specimens had wing-like feathers on their front legs, with downier feathers along their back and hips. The older specimen had larger, wing-type feathers on both the outermost and middle sections of its arms, while the younger one had the ribbon-like feathers on its middle arm section. The older dinosaur also had downy feathers along most of its spine and on its head.

The biggest difference, though, was an unusual type of feather found on the younger oviraptosaur that were thin and ribbon-like with tips that were tufted with normal feather growth. There were no feathers like this on the older oviraptosaur, suggesting that the tufted-tip feather was a developmentally intermediate stage of feather growth—individual dinosaurs first grew downy feathers, then thin, tufted-tip feathers, then full ones. By contrast, modern birds start growing full feathers as their down falls off.

Of course, these feather observations are drawn from only two oviraptosaurs, so it's possible that the tufted feathers are an anomaly, or a possibly the result of a poorly preserved specimen. Still, any related specimen should help our understanding of the role played by the earliest feathers.

Science, 2010. DOI: 10.1038/nature08965 (About DOIs).