Ever since the British biologist Thomas Huxley first proposed a close link between birds and dinosaurs in 1868, the idea has posed an intriguing question to historians of evolution: Did dinosaurs give extinction’s sickle the slip by morphing into modern day birds?
During the last 20 years, paleontologists have been piling up evidence in favor of birds’ dinosaurian origins. And when Sinosauropteryx, the so-called feathered dinosaur, was unearthed in China’s western Liaoning province a few years ago, many considered the case virtually closed.
A small but vocal minority, however, remain unconvinced, asserting instead that both birds and dinosaurs evolved from a common reptile ancestor. This family tree controversy is bound to receive a boost as National Geographic magazine presents the slabs of fossilized bones at its press conference Tuesday. A couple of the fossils are so sensational that National Geographic embargoed pictures of them and exacted a pledge of silence about them from the scientists involved.
According to Professor Ji Qiang at the National Geological Museum in Beijing, the fossils represent four steps in the evolution of dinosaurs to birds.
Besides two specimens of Sinosauropteryx, a specimen of the beaked bird Confusiusornis and a land-running bird, Protarchaeopteryx, two specimens of a previously unpublicized bird-dinosaur, Caudipteryx, will be presented by National Geographic at a press conference in Washington, D.C. “This is a great evolutionary happening connecting two different groups,” says Kevin Aulenback, a technician from the Royal Tyrell Museum in Alberta, Canada, who has studied the fossils and prepared casts of them. “Dinosaurs didn’t go extinct; they’re still alive.”
When photographs of Sinosauropteryx began circulating among paleontologists in 1996, they set off a heated debate over whether the bristle-like fibers along its back were rudimentary feathers or some other kind of integument. Nobody, however, questioned that seeing them as feathers required a leap of imagination. With the discovery of Protarchaeopteryx, a carnivorous bird-dinosaur with serrated teeth and massive wings, and Caudipteryx, which has shorter, more slender wings, a prominent tail and unserrated teeth, opponents of the dinosaur-bird link will have to come up with some pretty good arguments, since both animals have modern feathers on their wings and tails, and share features of both dinosaurs and birds. Caudipteryx is definitely a dinosaur, says a paleontologists who has studied the fossil but asked to not be identified.
The debate seems to cast as much light on the social psychology and factional politics of science as it does on the origin of birds. Proponents of the bird-dinosaur link are predominantly paleontologists, while the opponents tend to be ornithologists.
“It’s just a fantasy of theirs; they so much want to see living dinosaurs that now they think they can study them vicariously at the back yard feeder,” Alan Feduccia, an ornithologist at the University of North Carolina at Chapel Hill, said last year in Audubon magazine. In a 1996 interview in the journal Science, Feduccia said: “In my opinion, the theropod origin of birds will be the greatest embarrassment of paleontology in the 20th Century.”
Among the ornithologists’ weightiest assertions are that the small theropod dinosaurs appeared too late to give rise to birds, and that the complex lungs of birds could not have evolved from theropod lungs. Paleontologists, however, point to the amount of anatomical evidence in their favor.
“A lot of the bird anatomists don’t like birds coming from dinosaurs. They want them coming from small lizards,” says Kevin Aulenback of the Royal Tyrell Museum in in Canada.
In Washington, many Western scientists will be able to study the Chinese fossils for the first time. At the press conference, a re-creation of Caudipteryx, possibly the “missing link” between birds and dinosaurs, also will be presented. “It’s the one that has been well enough preserved to form the bridge,” says Philip Currie, curator of dinosaurs at the Royal Tyrell Museum.
Whatever the outcome of the debate, the Sihetun fossils are raising many questions. Why birds evolved feathers in the first place, for example. And which was the first bird to fly?
Caudipteryx and Protarchaeopteryx had feathers, but they are symmetrical, which indicates that they could not get off the ground. Archaeopteryx and Confusiusornis could fly, but possibly only from trees. According to Hou Lianhai at the Chinese Academy of Sciences, Liaoningornis, the first fossil of a bird with a keeled sternum developed enough to enable sustained flight was also found in Sihetun in the mid-1990s.
