Our fine-feathered friends ... dinosaurs?
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Three researchers - Dr. Holtz, Paul Sereno of Chicago's Field Museum of Natural History, and Mark Norell of New York's American Museum of Natural History - are trying to work the Chinese dinosaurs into their family trees.Skip to next paragraph
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And while they differ in some key details, the different versions are beginning to merge. "We're recognizing some fundamental relationships independently," Holtz notes. "That suggests these are well-supported relationships."
But in all of these new family trees, "T. rex is inside sino-sauropteryx," notes Jacques Gauthier, curator of vertebrate paleontology at the Peabody (Mass.) Museum. That means that at some point in T. rex's life, "it's got feathers."
Origin of feathers
Beyond the fossils' implication for dinosaurs' sartorial splendor lies the story they tell about feather evolution. "These three dinosaurs in particular have given us a great deal more insight into the origin of feathers," Dr. Gauthier says.
Faced with these fossils, as well as fossil feathers from the same period from elsewhere around the world, "the implication is that feathers evolved very rapidly," says Alan Brush, professor emeritus of biology at the University of Connecticut in Storrs.
"They are a simple innovation with a huge potential for evolution" because of their highly adaptable properties - from providing body contour and aerodynamic properties to warmth. Indeed, Gauthier adds, feathers probably functioned initially as insulators, holding in body heat. Later, they became crucial to surviving in a theropod-eat-theropod world.
He notes that in the mid-1980s, a physicist pointed out that gliding creatures increased their surface area from the body outward, while flying creatures increased their surface area away from their center of gravity. This gave them more lift.
"He showed that if you can gain enough lift at your outstretched hand to raise 1 percent of your body weight, you gain a lot in maneuverability," Gauthier says. In the run-or-be-eaten race, "everybody else can outrun you, so what's your advantage? Maneuverability."
Others add that wing motions evolved from the hunting techniques of coelurosaurs, whose shoulders and arms were structured in ways that allowed them to swing their arms down from above and behind their shoulders to grab and capture prey.
These theories strongly imply that flight originated from the ground up, rather than from the trees down. Some researchers have claimed that archaeopteryx, for example, lived in trees and flew by jumping to get enough acceleration to generate lift. Others hold that by running and flapping wings in a way that increases their angle of attack on the down stroke, the first flying theropods could generate enough lift to get them off the ground - particularly if they were running downhill.
"Every feature found in archaeopteryx to bolster it as a tree dweller also was present in tyrannosaurus rex," Gauthier says. "T. rex? A tree dweller? That's ridiculous."
Although a few researchers remain skeptical of the link between known theropods and birds, it remains "the best game in town in terms of the data that support it," Holtz says.
Indeed, the link is so tight, Gauthier adds, that it's time to acknowledge that "members of the Dinosaur Society and Audubon Society belong to the same club."