Stone, Richard

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508NEWS>>Q&A with IPCC chiefCan California’scoho salmon be saved?510 512BEIJING—Which came first, the chicken or thedinosaur egg? That one’s a cinch. Less obviousis the riddle of kinship. Most scientists thinkbirds evolved from dinosaurs about 150 mil-lion years ago. But a sparse fossil record hasprovided ammunition to those who insist thatbirds arose independently. A stunning new fos-sil makes that idea virtually untenable. And asecond paper this week brings dinosaur feath-ers vividly to life, offering new clues to whythis instrument of flight first evolved in flight-less creatures.On page 571, fossil-hunter extraordinaireXu Xing of the Institute of Vertebrate Paleon-tology and Paleoanthropology (IVPP) hereand colleagues unveil Haplocheirus sollers, anew genus of alvarezsauroid—a group ofdinosaurs once thought to be flightless birds.The nearly complete skeleton, unearthed from160-million-year-old mudstone deposits innorthwestern China’s Junggar Basin, extendsthe fossil record of alvarezsauroids back intime by a whopping 63 million years—making it about 15 million years older thanthe earliest known bird, Archaeopteryx.In 2006, specimens from another theropodgroup—tyrannosauroids—challenged the so-called temporal paradox: the fact thatirrefutable birdlike dinosaurs appear millionsof years after Archaeopteryx in the fossilrecord. (Among other birdlike features, tyran-nosauroids sport three-toed feet, hollow bones,and even wishbones.) Along with those andother recent finds, Haplocheirus “establishesonce and for all that there is no temporal para-dox,” asserts Hans-Dieter Sues, curator of ver-tebrate paleontology at the National Museumof Natural History in Washington, D.C.The newest, oldest alvarezsauroid dispelssome of the group’s mystique. “Alvarez-sauroids were collected for the first time in the1920s but were so enigmatic that they werenever recognized and describeduntil the 1990s,” says Philip Currie,a paleontologist at the University ofAlberta in Edmonton, Canada. Asspecimens turned up in Asia, Europe,and North America, debate raged overwhether they represented dinosaurs orflightless birds. Haplocheirus “definitelysettles this dispute,” Sues says. The exquis-itely preserved specimen “is so primitive,”says IVPP’s Zhou Zhonghe, that it lacks somebirdlike features seen in later alvarezsauroidssuch as fused wrist bones, a backward-facingpubis, or a crest near the top of the shinbone.The controversy highlights how hard it canbe to distinguish birds from dinosaurs. “Deepin evolutionary history, it’s extremely difficultto draw the line,” Xu says. The discovery offeathered dinosaurs in the late 1990s turnedclassification upside down. Why feathers evolved in dinosaurs is apuzzle. One idea is that feathers providedinsulation. Another is that they evolved ascamouflage or to attract a mate. But evidencesuch as distinctive colors or patterns hadeluded researchers—until now. This week inNature, paleontologist Mike Benton of theUniversity of Bristol in the United Kingdomand colleagues offer the f irst report oforganelles bearing the pigment melanin indinosaurs. They found melanosomes in thetheropods Sinornithosaurus and Sino-sauropteryx and in a bird, Confuciusornis, thatlived roughly 125 million years ago.Although many scientists expecteddinosaur feathers to contain melanosomes,finding them wasn’t easy. In Benton’s lab inBristol, IVPP’s Zhang Fucheng says he “spentday and night for more than a year” studyingscanning electron microscope images of scoresof fossil specimens. Zhang’s diligence paidoff—he uncovered melanosomes containingthe two most common kinds of the pigment:eumelanin, which gives a gray or black tinge,and pheomelanin, which gives a chestnut toreddish-brown color. The find could settlea debate over whether bristles studdingSinosauropteryx were primitive feathersor collagen fibers. “Melanosomes provethat those structures are indeed feathers,”Benton asserts.The discovery also reveals the truecolors of dinosaurs. Sinosauropteryx’sprotofeathers ran in alternating orangeand white rings down its tail like abarbershop pole. To Benton, thevibrant pattern suggests that “feath-ers first arose as agents for color dis-play and only later in their evolution-ary history did they become usefulfor flight and insulation.” Othersare not so sure. Zhou, a co-authorof the Nature paper, still thinksfeathers evolved for insulation.To Xu, the mystery has deep-ened. “Now we are realizing thatfeather evolution is more complexthan we thought,” he says.–RICHARD STONEBird-Dinosaur Link Firmed Up, And in Brilliant TechnicolorPALEONTOLOGYCREDITS: (LEFT) ARTWORK BY CHUANG ZHAO AND LIDA XING; F. ZHANG ET AL., NATURE(ADVANCED ONLINE EDITION) © 2010 NATURE PUBLISHING GROUP, MACMILLAN PUBLISHERS LIMITED; (RIGHT) PORTIA SLOAN29 JANUARY 2010 VOL 327 SCIENCE www.sciencemag.orgBirds of a feather. A new avianlike alvarezsauroid(below) predates the first bird, Archaeopteryx—powerful evidence that birds arose fromdinosaurs. Fossilizedpigment organellesreveal the truecolors of Sino-sauropteryx(left). Published by AAAS on January 28, 2010 www.sciencemag.orgDownloaded from 

Bird-dinosaur link firmed up, and in brilliant technicolor

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