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Wings over Spain
Natural History, Sept, 1998 by Luis M. Chiappe
RELATED ARTICLE: First Came Feathers
Our language has its share of sayings when it comes to birds. Birds of a feather flock together. If it walks like a duck and quacks like a duck, it must be a duck. These are a couple that come to mind. For better or worse, these old saws might require some revision, based on discoveries of two new fossil animals from northeast China.
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The two turkey-sized creatures were found m fine-grained lake sediments, estimated to be 135 million to 122 million years old, near Beipiao City, in Liaoning Province. They belong to the coelurosaurs, a group of theropod dinosaurs that now includes birds. The Chinese fossils have a whole slew of features--hollow bones, flexible wrists, and wishbones, to name a few--that ally them with birds, and whose presence in other coelurosaurs have for mine time indicated to paleontologists that birds are the descendants of coelurosaurian dinosaurs. Other features--including an opposable hallux (or back toe) and smooth-enameled teeth--are characteristics of Mesozoic birds and are not present in the Liaoning animals. But the new fossils consist of more than bones and teeth; they contain remarkably well preserved feathers. The presence of feathers in animals that are not birds forever blurs the distinction between birds and their closest relatives and indicates that feathers alone are not sufficient evidence for calling something a bird.
Named Protoarchaeopteryx and Caudipteryx (tail feather), the Chinese animals have feathers that are quite similar to those of modern birds. The feathers cover the entire body and have central shafts with branching barbs. Scanning electron microscopy shows that the barbs are held in alignment by smaller barbules--tiny, Velcro-like hooks that give feathers their neat appearance, even after a fair amount of ruffling. As in modern birds, the long arm feathers (preserved in Caudipteryx but not in Protoarchaeopteryx) emanate from the hand, although the primary feathers of modern flying birds tend to be even longer. In the dinosaurs, the barbs are distributed symmetrically on either side of the shaft, unlike the asymmetric, and more aerodynamic, distribution of barbs found in the wing feathers of modern birds. Both Protoarchaeopteryx and Caudipteryx have long tails covered in feathers with a flourish at the tip: a clump of feathers that form a fan.
Although fully feathered, neither Protoarchaeopteryx nor Caudipteryx could fly. The origin of feathers and the origin of flight are separate issues. Likely scenarios for the evolution of feathers concern their use for display or insulation. Patches of downlike feathers on some parts of the Chinese animals appear, in my opinion, to support the insulation argument, as does the remarkable fluffy covering of another, much more primitive coelurosaur from the same deposits, Described in 1997, Sinosauropteryx is known from several specimens, all of which show this covering. While not consisting of true feathers, this feature is also powerful evidence that its coelurosaurian relatives, such as Velociraptor, Troodon, and even Tyrannosaurus, were also cloaked in protofeathers.
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