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Scaly New Dinosaur Creates Flap Over Feathers' Evolution

James Owen
for National Geographic News
March 15, 2006
 
The fossil of a small, predatory dinosaur discovered in Germany has experts rethinking how feathers developed among the dinosaurs that likely gave rise to birds.

The small, long-tailed predator lived some 150 million years ago. Experts say the fossil represents the best example of a European dinosaur from this period. The fossil was discovered in limestone rock from Bavaria, in southern Germany (map).

The specimen includes sections of fossilized skin that shows no evidence of feathers, despite the fact that the dinosaur's Jurassic-age contemporaries from the same group were feathered.

Described in tomorrow's issue of the journal Nature, the new species, Juravenator starki, belongs to a group of theropods—meat-eating, two-legged dinosaurs—that many scientists believe also gave rise to birds.

The authors say the new species undermines the notion that a covering of simple, hairlike feathers was characteristic of such early theropods as was previously believed.

"Given the worldwide rarity of complete specimens of small theropods from the Jurassic, the exceptionally well-preserved skeleton of Juravenator is in itself a notable find," writes paleontologist Xing Xu in a commentary accompanying the study.

"Most significantly," he writes, "the specimen preserves scaled skin around the tail and hind limbs. This is a big surprise."

The find will encourage a re-evaluation of feather evolution in dinosaurs, adds Xu, who teaches at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China.

Luis Chiappe, associate curator at California's Natural History Museum of Los Angeles County, and Ursula Gohlich of the University of Munich in Germany report the find in the Nature study.

Earliest Bird

The area where Juravenator was found is famous as the source of fossils of Archaeopteryx, the earliest known bird.

"The new fossil is the best preserved predatory, nonavian dinosaur in Europe," the study authors write.

The 75-centimeter-long (30-inch-long) dinosaur likely hunted lizards, insects, and other small prey, possibly including mammals, according to Chiappe.

The authors argue that the animal provides evidence that some early dinosaurs developed feathers faster than their relatives.

"The fact that Juravenator lacks any of these feathers," they write, "indicates that these animals may have differed greatly in the extension of their feathery covering."

The most primitive known feathered dinosaur is Sinosauropteryx, which lived 120 to 150 million years ago.

"These animals look quite similar to one another, and that makes the lack of feathers in Juravenator most interesting," Chiappe said in an interview.

Fossils of several other early theropod dinosaurs have shown evidence of feathers, including a species described by Xu in 2004 that was an ancestor of Tyrannosaurus rex. (Read "New Dinosaur Discovered: T. Rex Cousin Had Feathers")

Theories differ as to why some dinosaurs that weren't birds had feathers. Some suggest that the plumage may have been used for keeping warm or for display.

"The earliest structures interpreted as feathers do not show aerodynamic specializations—they lack vanes and they don't form an airfoil," Chiappe said, explaining that the feathers could not have been used for flight.

"It is also possible that feathers evolved in the context of display to attract mates or to help the identification of suitable mates of a same species," he added.

Unique Feature

Because feathers are a unique feature, they are thought to be characteristic of many theropod dinosaurs, including tyrannosaurs.

Given its position in the dinosaur family tree, Juravenator "should bear filamentous feathers," Xing Xu said in an interview.

In seeking to explain its lack of feathers, he says it's possible the species didn't grow feathers on areas of its body where the skin was preserved.

The new species may have been more scaly than modern birds, which have scales only on their legs, he added.

A scaly Juravenator, Xu said, could be a "starting point for feather evolution."

But Chiappe's theory differs.

"If the absence of feathers in Juravenator can be explained by arguing that feathers had not yet evolved, the animal needs to be even more primitive than [tyrannosaurs], and I find this hard to believe," Chiappe said.

For his part, Xu notes that some "otherwise beautifully preserved" specimens of the first bird, Archaeopteryx, had been found in which feathers didn't survive.

"Feather preservation is extremely rare," he added.

But Chiappe says the new fossil didn't seem to bear any physical evidence of feathers, missing or not.

"You could expect to see follicle [in the skin], small pits that contain feather buds. We don't see them in Juravenator," Chiappe said.

Xu proposes that feathers may have evolved independently several times in similar groups of dinosaurs.

"Even after the discoveries of so many fossils of feathered dinosaurs, we still have only a patchy picture of feather distribution," he said.

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