April 28, 2010 at 8:30 PM ET
Xing Lida and Song Qijin
Scientists say the feathers of early and late juvenile Similicaudipteryx dinosaurs
had markedly different looks, especially on the wings and tail, as shown here.
A rare fossil find from China reveals how dinosaurs' feathers changed as the creatures matured. The discovery, announced in this week's issue of the journal Nature, suggests that dinosaurs molted like modern-day birds do - even though their feathers developed in an un-birdlike way.
"This find suggests that early feathers were developmentally more diverse than modern ones and that some developmental features ... have been lost in feather evolution," the researchers wrote.
The team includes the Chinese Academy of Science' Xing Xu, one of the world's best-known paleontologists, as well as Xiaoting Zheng of the Shandong Tianyu Museum of Nature and Hailu You of the Chinese Academy of Geological Sciences.
China is the world's hottest hotspot for feathered dinosaurs, but even in China, it's unusual to find two specimens from the same species but in different stages of development. The two fossils recovered from the Yixian Formation in western Liaoning date back about 125 million years, and clearly show traces of feathers. What's most significant for this study is that they represent a young juvenile and a not-so-young juvenile, Xu and his colleagues said.
The younger dino sported feathers on its tail and wings that started out as ribbons, flat and straight, and spread out toward the end into a quill-like configuration. In contrast, the older relative had the full quill treatment.
That developmental pattern is "not known in any modern bird," the researchers said.
Modern-day chicks are covered with downy feathers when they're born - and it could well be that dino hatchlings came out of their eggs the same way. But when chicks get their second round of feathers, they're essentially the same type of feathers that the birds have for the rest of their lives. The dino fossils, however, suggest that significant changes took place in the shape of the feathers even after the hatchling stage. There's a chance that the feathers morphed from the ribbon-quill hybrid into pure quills as the animals grew, but it's more likely that the early feathers were shed, to be replaced by a new coat.
Another change had to do with the relative size of the feathers: The youngster's tail feathers were larger than the wing feathers, while the older dino's wing feathers were larger than the tail feathers. That may reflect "an increase in the functional role" of the wings as the dinosaurs matured, the researchers said.
In their paper, Xu and his colleagues delve into the potential genetic mechanisms behind dino-feather morphology. They note that even within the dinosaur tribe, feathers of different patterns have been found. The bottom line? Evolution may well have streamlined the process by which the dinosaurs and their descendants made feathers.
Learn more about the discovery:
Xing et al. / Nature
These pictures show the differences between the early juvenile and late juvenile
fossils of Similicaudipteryx. The top left photo marked "a" shows the early juvenile;
at top right, "b" shows tail feathers, "c" shows wing feathers. The lower left photo
("d") shows the late juvenile, with tail feathers ("e") and wing feathers ("f").