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New feathered dinosaur specimen strengthens dino-bird link

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feathered dinosaur four wings fossilNon-avian dinosaurs are long extinct, but paleontological thinking about them, especially the dino–bird specimens, clearly continues to evolve long after they are discovered. For instance, the Anchiornis huxleyi, a small, feathered dinosaur, was described last December and assumed to be a transitional species that existed between dinosaurs and birds. But new evidence—and a much better specimen—has revealed that this ambiguous animal actually belongs to the dinosaur clan.

Described from a partial specimen in the Chinese Science Bulletin, A. huxleyi was proposed to be an "intermediate…between non-avian and avian dinosaurs," wrote Xing Xu, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing, and his colleagues. But as a dinosaur—now proposed to be a troodontid, a birdlike group of theropods—it sets the clock back for bird evolution. 

The dinosaur–bird transition has been the subject of debate for more than a century, and some researchers are still arguing that other birdlike dinos are too recent to be the ancestors of birds. The quandary, known in the paleontology field as the temporal paradox, has been dealt another blow by the reassessment of the A. huxleyi, which is dated to about 155 million years old—about 30 million years before the feathered dinosaur Microraptor and about five million years before the oldest known bird, Archaeopteryx. This earlier date for the emergence of feathered dinosaurs undermines claims that birds lacked enough time to evolve from dinosaurs.
feathered dinosaur four wings diagram
In addition, the research "sheds new light on the early evolution of feathers and demonstrates the complex distribution of skeletal…features close to the dinosaur–bird transition," the paper authors write [pdf] in the letters section of Nature this week (Scientific American is part of the Nature Publishing Group).

Adding lift to the theory that these animals once flew or glided with all four wings, the A. huxleyi appears to have had several contour features (aka pennaceous feathers)—found on modern birds—on its hind legs. The authors of the most recent paper, to which Xu also contributed, note that this supports the idea that feathers developed first on the tail region of dinosaurs and spread later to the forewings, before disappearing from the legs of contemporary birds.

Both specimens were unearthed in the Tiaojishan Formation in Liaoning, China. The small dinosaur originally described in the Chinese Science Bulletin measures about 34 centimeters long and weighed about 110 grams. Although it might have played a part in ushering in a brave new world for birds, the A. huxleyi is named not for the famed science-fiction author, but for Thomas Henry Huxley, an early advocate of evolution and one of the first people to suggest that birds may indeed be descended from dinosaurs.

Images courtesy of Xing Xu et al.





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  1. 1. coolmoss 7:19 pm 09/24/2009

    Regardless of whether or not Anchiornis huxleyi represents a transition between dinosaur and bird, it does reveal the available raw material needed for natural selection to take it’s course. In other words, A huxleyi represents at least some form of collateral ancestry. And the more ancestors there are like this, the more birds are just a matter of time.

    Link to this
  2. 2. leeyahao 3:41 am 09/25/2009

    Although the details of the dinosaur-bird transition are still ambigous,more and more fossils were found to establish a toutine of evolution from dinosaur to bird.

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  3. 3. loken kristianna 2:29 am 10/5/2009

    I don’t mean this fossil tells us nothing. Every well-preserved new
    dinosaur species tells us something. I just mean that the mere fact of
    it being a troodont with feathers tells us nothing we didn’t already
    know; same with its age.
    Adding lift to the theory that these animals once flew or glided with all four wings, the A. huxleyi appears to have had several contour
    features (aka pennaceous feathers)–found on modern birds–on its hind
    legs. The authors of the most recent paper, to which Xu also
    contributed, note that this supports the idea that feathers developed
    first on the tail region of dinosaurs and spread later to the
    forewings, before disappearing from the legs of contemporary birds.
    Conceivably this is actually something new. Depends on what the Nature
    paper really says, and whether this troodont has flight feathers on its
    forelimbs too.
    <a href="http://www.vitabits.fr/antioxydants/">acai berry</a>

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  4. 4. lrejec 6:30 am 10/10/2009

    I would like some clarification on the following statement, because it appears there must be an error somewhere:

    "The small dinosaur originally described in the Chinese Science Bulletin measures about 34 inches long and weighed about 110 grams."

    If my guesstimate is correct, this indicates the creatures was nearly a metre long and weighed just a tenth of a kilogram. I can’t help but be incredulous at this data, when even a twenty centimetre (7 inch) fish weighs more …

    Link to this

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