More birdlike behavior in theropod dinosaurs

In WEIT I describe and show a picture of birdlike sleeping behavior in theropod dinosaurs: a fossil was discovered of a therpod sleeping with its head tucked underneath its forelimb (and tail curled around), a posture nearly identical to the sleeping posture of modern birds. Now an article has appeared in PLoS (Public Library of Science) showing even more birdlike behavior of theropods: “Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace,” by Andrew R. C. Milner, Jerald D. Harris, Martin G. Lockley, James I. Kirkland, and Neffra A. Matthews, which you can find here.

It turns out that Milner et al. uncovered several sets of theropod tracks from fine Utah sandstone about 198 million years old. They show the impressions of theropods of the species Eubrontes gigante and Dilophosaurus wetherilli walking (and dragging their tails), as well as resting on both hind AND front legs. (Front-leg impressions are rare in theropods since they were obligately bipedal.) When the beast rested, it brought its hindlimbs (manus) together symmetrically (in line) and rested its forlimbs (pes) on the ground, with the hands pointing inwards (see the impressions in the original article showing handprints). The authors conclude that theropod hands always faced inwards when the arms were stretched out–a configuration identical to that of modern birds. Apparently the palms-in position evolved very early in the theropods, presumably to help them grasp prey.

The more we learn about theropods, the more we see that many of the features that were later co-opted in flight were “pre-adaptations”–that is, traits evolved for one use in the theropods that were later hijacked for flying by their bird descendants. Another such feature is feathers, which we’ll discuss tomorrow. Clearly, the evolution of birds from dinosaurs was not as mysterious and maladaptive as touted by creationists. As is usual in evolution, new adaptations are simply old ones that have been refashioned.

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Reconstruction of the theropod Dilophosaurus wetherilli resting after having walked on mud. Note inward-facing palms. See original paper for the tracks that led to this reconstruction. Drawing taken from Milner et al. paper.

5 Comments

  1. Adam
    Posted March 19, 2009 at 11:38 am | Permalink

    You said “a fossil was discovered of a therpod sleeping with its head tucked underneath its forelimb”. How can they know for sure — sure enough to make that unqualified statement — that it was sleeping?

  2. whyevolutionistrue
    Posted March 19, 2009 at 11:43 am | Permalink

    Adam: It wasn’t simply an artifact of preservation. See the photo in my book and the original paper:

    Xu, X., and M. A. Norell. 2004. A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431:838-841.

  3. Adam
    Posted March 20, 2009 at 4:59 am | Permalink

    Well, I tried but I guess I’m not willing to pay $32 to read the article or $200 to subscribe to the journal, plus the cost of buying and shipping your book to my little country (where it’s not available in stores)…

    Can you not summarize?

  4. Sili
    Posted March 22, 2009 at 6:56 am | Permalink

    Obligatory pimping of the artist goes here.

  5. David Ratnasabapathy
    Posted March 23, 2009 at 1:53 pm | Permalink

    Adam: you can view selected pages of the book at amazon.com. Search for “theropod sleeping” — the reference is on page 44, the picture is on the following page.


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