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Scaly Dino Find Complicates Feather Evolution

juravenator fossil



G. JANSSEN
Paleontologists working in the same area of Germany that yielded Archaeopteryx have discovered a new small theropod dinosaur. The nearly complete specimen--dubbed Juravenator starki--is one of just a few known fossils representing this group, which ultimately gave rise to modern birds. Indeed, it joins just two partial skeletons of another genus as the only European examples of the tiny carnivores. Unlike the other two specimens, however, it lacks any sign of feathers, complicating what researchers thought they knew about feather evolution.

The Juravenator skeleton measures just 25 inches from snout to tail, with much of that length in the tail itself. Strong scarring and pitting of its bones mark it as a juvenile, however, and adults may have grown another six inches. Armed with three-pronged claws and serrated teeth, it lived roughly 151 million years ago in the Late Jurassic period.

In a paper describing the fossil, published today in Nature, Luis Chiappe of the Natural History Museum of Los Angeles and Ursula Gohlich of the University of Munich classify Juravenator as an early member of the coelurosauria family that eventually evolved into birds, but one that lived later than some of the early feathered representatives. In fact, the discovery of feathers in a wide variety of coelurosaurs had led experts to posit that the entire clade had the downy covering. But Juravenator's skin impressions--seen in the middle of its tail and on its hind legs--show only scales.

This could mean that feathers evolved, were lost and then regained in the lineage or that the creature shed its coat during different seasons, the researchers write. Or it could be that Juravenator is more primitive than they suggest, argues Xing Xu of the Chinese Academy of Sciences in Beijing in an accompanying commentary. "Whatever the explanation, our knowledge of early feather evolution has been enriched by the discovery," Xu writes. "Juravenator may complicate the picture, but it makes it more complete and realistic."

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