Bird-Dinosaur Link Firmed Up, and in Brilliant Technicolor
Total Page：16
File Type：pdf, Size：1020Kb
NEWS>> Q&A with Can California’s IPCC chief coho salmon be saved? 510 512 PALEONTOLOGY The controversy highlights how hard it can be to distinguish birds from dinosaurs. “Deep in evolutionary history, it’s extremely difficult Bird-Dinosaur Link Firmed Up, to draw the line,” Xu says. The discovery of feathered dinosaurs in the late 1990s turned And in Brilliant Technicolor classification upside down. Why feathers evolved in dinosaurs is a BEIJING—Which came first, the chicken or the irrefutable birdlike dinosaurs appear millions puzzle. One idea is that feathers provided dinosaur egg? That one’s a cinch. Less obvious of years after Archaeopteryx in the fossil insulation. Another is that they evolved as is the riddle of kinship. Most scientists think record. (Among other birdlike features, tyran- camouflage or to attract a mate. But evidence birds evolved from dinosaurs about 150 mil- nosauroids sport three-toed feet, hollow bones, such as distinctive colors or patterns had lion years ago. But a sparse fossil record has and even wishbones.) Along with those and eluded researchers—until now. This week in provided ammunition to those who insist that other recent finds, Haplocheirus “establishes Nature, paleontologist Mike Benton of the birds arose independently. A stunning new fos- once and for all that there is no temporal para- University of Bristol in the United Kingdom sil makes that idea virtually untenable. And a dox,” asserts Hans-Dieter Sues, curator of ver- and colleagues offer the first report of second paper this week brings dinosaur feath- tebrate paleontology at the National Museum organelles bearing the pigment melanin in ers vividly to life, offering new clues to why of Natural History in Washington, D.C. dinosaurs. They found melanosomes in the this instrument of flight first evolved in flight- The newest, oldest alvarezsauroid dispels theropods Sinornithosaurus and Sino- less creatures. some of the group’s mystique. “Alvarez- sauropteryx and in a bird, Confuciusornis, that on January 28, 2010 On page 571, fossil-hunter extraordinaire sauroids were collected for the first time in the lived roughly 125 million years ago. Xu Xing of the Institute of Vertebrate Paleon- 1920s but were so enigmatic that they were Although many scientists expected tology and Paleoanthropology (IVPP) here never recognized and described dinosaur feathers to contain melanosomes, and colleagues unveil Haplocheirus sollers, a until the 1990s,” says Philip Currie, finding them wasn’t easy. In Benton’s lab in new genus of alvarezsauroid—a group of a paleontologist at the University of Bristol, IVPP’s Zhang Fucheng says he “spent dinosaurs once thought to be flightless birds. Alberta in Edmonton, Canada. As day and night for more than a year” studying The nearly complete skeleton, unearthed from specimens turned up in Asia, Europe, scanning electron microscope images of scores 160-million-year-old mudstone deposits in and North America, debate raged over of fossil specimens. Zhang’s diligence paid northwestern China’s Junggar Basin, extends whether they represented dinosaurs or off—he uncovered melanosomes containing www.sciencemag.org the fossil record of alvarezsauroids back in flightless birds. Haplocheirus “definitely the two most common kinds of the pigment: time by a whopping 63 million years— settles this dispute,” Sues says. The exquis- eumelanin, which gives a gray or black tinge, making it about 15 million years older than itely preserved specimen “is so primitive,” and pheomelanin, which gives a chestnut to the earliest known bird, Archaeopteryx. says IVPP’s Zhou Zhonghe, that it lacks some reddish-brown color. The find could settle In 2006, specimens from another theropod birdlike features seen in later alvarezsauroids a debate over whether bristles studding group—tyrannosauroids—challenged the so- such as fused wrist bones, a backward-facing Sinosauropteryx were primitive feathers called temporal paradox: the fact that pubis, or a crest near the top of the shinbone. or collagen fibers. “Melanosomes prove Downloaded from that those structures are indeed feathers,” SLOAN PORTIA (RIGHT) LIMITED; PUBLISHERS MACMILLAN GROUP, PUBLISHING NATURE 2010 © EDITION) ONLINE (ADVANCED Birds of a feather. A new avianlike alvarezsauroid Benton asserts. NATURE (below) predates the first bird, Archaeopteryx— The discovery also reveals the true , powerful evidence that birds arose from colors of dinosaurs. Sinosauropteryx’s AL. ET dinosaurs. Fossilized protofeathers ran in alternating orange pigment organelles and white rings down its tail like a reveal the true barbershop pole. To Benton, the colors of Sino- sauropteryx vibrant pattern suggests that “feath- (left). ers first arose as agents for color dis- play and only later in their evolution- ary history did they become useful for flight and insulation.” Others are not so sure. Zhou, a co-author of the Nature paper, still thinks feathers evolved for insulation. To Xu, the mystery has deep- ened. “Now we are realizing that feather evolution is more complex than we thought,” he says. –RICHARD STONE ZHANG F. XING; LIDA AND ZHAO CHUANG BY ARTWORK (LEFT) CREDITS: 508 29 JANUARY 2010 VOL 327 SCIENCE www.sciencemag.org Published by AAAS.