Feathers for T. rex? New birdlike fossils are missing links in dinosaur evolution.

DINOSAURS will never look the same. The reason: four new dinosaur fossils with stunningly birdlike bones and indications of feathers. Not enough to prove that these dinosaurs ever flew but strong evidence that feathers were widespread among meat-eating dinosaurs--the group that includes Tyrannosaurus rex.

Three of the fossils were found recently in Liaoning Province, China, the area that produced fossils of flightless feathered dinosaurs in 1996-97. All four are theropods, or meat-eaters: a dromaeosaur, one of a family of small- to medium-size predators that includes Jurassic Park's "raptors"; an oviraptorosaur from Mongolia with a birdlike tail; a seven-foot-long therizinosaur; and a creature that has the arms of a bird and the tail of a dinosaur.

Twenty years ago when John Ostrom, a respected paleontologist at Yale University's Peabody Museum of Natural History, proposed that birds descended from theropods, many scientists viewed him as a radical. But the clear impressions of feathers on the Liaoning fossils lengthen the list of feathered theropods, and we can now say that birds are theropods just as confidently as we say that humans are mammals. Everything from lunch boxes to museum exhibits will change to reflect this revelation.

A simple paper sign with "Chris" scribbled on it, tacked to a weathered post, is my signal to turn into the Czerkas ranch in southeastern Utah. Ifs May 1999, and I'm about to meet up with one of the Chinese specimens that, right now, only a few people know about. Stephen and Sylvia Czerkas, directors of the Dinosaur Museum in Blanding, found it early this year at a gem and mineral show. Immediately recognizing its scientific value, they found benefactors and purchased it quietly, planning to give it a home in the museum. "We wanted to make sure it didn't end up on a mantel in someone's private collection," says Sylvia.

According to Chinese officials any fossils leaving China--including countless bird specimens and dinosaur eggs that have appeared on the international market--are illegal exports. So, after completing their study of the fossil, the Czerkases now plan to return it to China.

Stephen draws me into a back room to view the animal he will later name Archaeoraptor liaoningensis, I've seen feathered dinosaur specimens, but what Stephen shows me takes my breath away. Its long arms and small body scream Bird!" Its long, stiff tail--which under magnification erupts into a series of tiny support rods paralleling the vertebrae--screams "Dinosaur!"

Surrounding the bones, which suggest that the animal is a dromaeosaur-like primitive bird, are the remains of feathers. Some are similar to the hairlike protofeathers of the flightless Sinosauropteryx round in 1996.(*) But others look long and broad, seductively suggesting flight feathers. "Ifs a missing link," Stephen says. "We can't prove that it flew, but even aside from its feathers, its anatomy--long arms, birdlike shoulders, hands, and wrists--doesn't make sense unless it did."

Three weeks earlier I had viewed the other two Liaoning fossils at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. The first, a dromaeosaur, was an eagle-size creature named Sinornithosaurus millenii, "Chinese bird-reptile of the millennium." It was exquisitely fierce looking, with barracuda-like teeth and long curved claws. It reminded me of John Ostrom's description of dromaeosaurs: "bizarre killing machines."

Paleontologist Xu Xing showed how the bones of Sinornithosaurus millenii's shoulder girdle--the scapula, coracoid, and furcula--are more like those of a bird than those of a dinosaur. Critical for flight, these bones join at the glenoid fossa, a cup-shaped area that determines the degree to which a bird can raise its wings above its shoulder to flap. "If you saw just this shoulder girdle, you would think it was Archaeopteryx, the earliest bird," he said.

In a room across a dimly lit hall Xu showed me the other feathered theropod, Beipiaosaurus inexpectus, one of only a few therizinosaur specimens known. Farmers discovered the gray bones near the town of Beipiao and discarded them, believing they had no commercial value. Xu and his colleagues chanced upon scraps of the fossil and salvaged the remaining pieces from the site.

The young scientist handed me a flat piece of rock about the size of my hand. It bore pink comblike impressions that suggested stiff, narrow feathers. "These filaments might have had hollow cores," he said. This is a key feature, since hollow, hairlike structures characterize protofeathers--evolutionary intermediates between reptilian skin and feathers.

At seven feet long, Beipiaosaurus is the largest dinosaur yet found with feathers. But why did it have them, since neither this therizinosaur nor its ancestors ever flew? One explanation is that their feathers did not evolve for flight but for insulation--which gives rise to another question: Were dinosaurs warm-blooded?

Biologist Mary Schweitzer of Montana State University, who has studied the small fibrous structures on a birdlike creature from Mongolia named Shuvuuia deserti, is helping to answer that question. Her tests show that the fibers are similar, chemically and structurally, to modern feathers. "The only animals living today with body coverings of hair or feathers have the high metabolic rates of warm-blooded creatures," she says. "It seems reasonable to assume that this was true in the past as well. Dinosaurs that possessed body coverings were probably either warm-blooded or had metabolic rates significantly higher than those of modern cold-blooded animals."

But the larger an animal becomes, the less likely it is to need a coat of hair or feathers for insulation, since large bodies generate more heat. The last thing an adult T. rex in a subtropical Cretaceous world would have needed was a warm coat. "If adult T. rex had feathers, it was probably only for display," says Philip Currie, theropod expert and curator of dinosaurs at the Royal Tyrrell Museum in Drumheller, Alberta.

But what about T. rex juveniles? "Baby animals have less control of their body temperature than adults," says Currie. "T. rex hatchlings needed a way to stay warm. What would be more logical than insulating feathers?"

A photograph of a bird in flight freezes its wings in a pose--a mere suggestion of the complicated process of flight. In a similar way the new Liaoning fossils create a snapshot of reptilian skin evolving into feathers. Perhaps someday a new discovery will capture the moment when a flying dinosaur became a bird.

A FLYING DINOSAUR?

"IT'S A MISSING LINK between terrestrial dinosaurs and birds that could actually fly."

--STEPHENS CZERKAS

With arms of a primitive bird and the tail of a dinosaur, this creature found in Liaoning Province, China, is a true missing link in the complex chain that connects dinosaurs to birds. Scientists funded by National Geographic studied the animal, named Archaeoraptor liaoningensis, under ultraviolet light (above) and used CT scans to view parts of the animal obscured by rock. Preliminary study of the arms suggests that it was a better flier than Archaeopteryx, the earliest known bird. Its tail, however, is strikingly similar to the stiff tails of a family of predatory dinosaurs called dromaeosaurs. This mix of advanced and primitive features is exactly what scientists would expect to find in dinosaurs experimenting with flight. Stephen Czerkas, who led the study of the specimen, reconstructed the new animal (inset), which resembles Archaeopteryx. "This fossil is perhaps the best evidence since Archaeopteryx that birds did, in fact, evolve from certain types of carnivorous dinosaurs," says Czerkas.

FEATHERED PREDATOR

We can now say that BIRDS ARE THEROPODS just as confidently as we say that humans are mammals.

Halo of feathers radiates from the fossilized bones of Sinornithosaurus millenii (left), which lived more than 120 million years ago. A sculptor's depiction (above) shows it pursuing prey; it probably fed on lizards and small mammals. Although the creature was apparently covered with downy feathers, it could leap but not fly. However, its boomerang-shaped furcula, or wishbone (far right), resembles that of the primitive bird Archaeopteryx, according to paleontologist Xu Xing. Resting near two claws, the tail vertebrae anchor bundles of slim bony rods (below) that stiffened the tail to aid maneuverability. This feature identifies Sinornithosaurus as a dromaeosaur, one of the most effective predators of its day. The fossil also supports the concept that early feathers evolved for insulation or display rather than flight and adds new weight to the idea that these dinosaurs were warm-blooded.

PREPARING FOR TAKEOFF

Pointed sign on the evolutionary road to avian flight, the last five vertebrate on the tail of a Mongolian oviraptorosaur are fused into a pygostyle, which in birds holds tail feathers that serve as crucial flight-control aids. In this dinosaur, however, the pygostyle may have supported feathers for sexual display.

Acting as a counterbalance, the tail of Velociraptor is composed of many vertebrate. In an oviraptorosaur the tail has fewer vertebrate and ends with an incipient version of the pygostyle. As birds evolved, the tail drastically shortened, as in an eagle. The pygostyle's tail feathers serve the bird in flight maneuvers and in displays to attract mates and intimidate rivals.

(*) See "Dinosaurs Take Wing," by Jennifer Ackerman, in the July 1998 NATIONAL GEOGRAPHIC.

For a 3-D view of a feathered dinosaur, go to www.nationalgeographic.com/dinorama.

Former Senior Assistant Editor Lou MAZZATENTA photographed evidence of the earliest lire on Earth for the magazine's March and April 1998 issues.

Source Citation
Sloan, Christopher P. "Feathers for T. rex? New birdlike fossils are missing links in dinosaur evolution." National Geographic Nov. 1999: 98+. Academic OneFile. Web. 13 Nov. 2009. .

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