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Research Article

Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace

  • Andrew R. C. Milner mail,

    amilner@sgcity.org

    Affiliation: St. George Dinosaur Discovery Site at Johnson Farm, St. George, Utah, United States of America

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  • Jerald D. Harris,

    Affiliation: Dixie State College, St. George, Utah, United States of America

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  • Martin G. Lockley,

    Affiliation: Dinosaur Tracks Museum, University of Colorado at Denver, Denver, Colorado, United States of America

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  • James I. Kirkland,

    Affiliation: Utah Geological Survey, Salt Lake City, Utah, United States of America

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  • Neffra A. Matthews

    Affiliation: National Operations Center, USDOI-Bureau of Land Management, Denver, Colorado, United States of America

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  • Published: March 04, 2009
  • DOI: 10.1371/journal.pone.0004591
  • Featured in PLOS Collections

Reader Comments (3)

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Alternative interpretations?

Posted by AndyFarke on 05 Mar 2009 at 05:33 GMT

The medially, not cranially, oriented manual digits indicate that even while resting, the track maker was incapable of supinating its hands to create palms-down impressions, as suggested by anatomical studies of geologically much younger theropods.
http://plosone.org/article/info:doi/10.1371/journal.pone.0004591#article1.body1.sec3.p3

Could it be argued that this just reflects a preferred resting position, rather than an anatomical restriction? Some good Early Jurassic dinosaur forelimbs (which I realize aren't exactly plentiful in uncrushed form) would do much to help verify mobility possibilities.


RE: Alternative interpretations?

JDHarris replied to AndyFarke on 05 Mar 2009 at 14:49 GMT

It's certainly possible that this reflects a preferred resting position, but we were hard pressed to think that, if pronation were possible, that it would prefer to rest its hands in what appears to be an awkward position. After all, humans can rest their hands this way, but don't (not that I'm by any means advocating humans as a good proxy for theropod behavior!) Actually, we think it's really unusual that its hands got anywhere near the sediment to begin with -- though, again, it's known with more commonality in later theropods, we'd've thought the preferred position would be to have the arms tucked up! But you're absolutely correct -- functional studies on early theropod limbs is <i>exactly</i> what's called for...and yup, it's unfortunate that most of the stuff this age is half mangled by diagensis, when good complete arms and wrists are preserved at all...!