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Re: And the Largest Theropod Is....

Ekaterina Amalitzkaya (a_ekaterina@yahoo.com) wrote:

<Is it justified to reconstruct Deinocheirus based on the
Ornithomimosaurs? Is it not really way too large compared to any of the
other ornithomimosaurs. Given the goose like lifestyle predicted for the
Ornithomimosaurs could that have been sufficient to sustain something as
big as Deinocheirus? Are there any diagnostic features in the other
elements, beyond the fore limbs, that support a linkage between to the
o'mimosaurs?. Deinocheirus seems as enigmatic as before, a Bullockornis of
its times?>

  The humerus and manus indicate that *Deinocheirus* is an
ornithomimosaur. No other taxa share the suite of features found in
ornithomimosaurs that would imply an alternate relationship for
*Deinocheirus*, despite its size. Restoring *Deinocheirus* as a giant
*Gallimimus*-shaped animal, as Gurney did for "Dinotopia," would be a
fallacy based on general allometry: for one thing, the scapula of
*Deinocheirus* scaled to an ornithomimosaur of the same humeral length
would indicate a VERY long bone for the trunk size, similar to that found
in therizinosaurs. This may reflect the large volume of the trunk,
possibly convergent with therizinosaurs. *Deinocheirus* lacks features of
therizinosaurs in the arm or manus, even though the manual claws are
recurved and large they are within size proportions of *Gallimimus*
relative to the fingers, and their curvature only a few degrees in
curvature greater. The humerus is the biggest clue, given that for such a
huge arm, it retains the slender caput, distal end, shaft, and small
deltopectoral crest and adductor crest of ornithomimosaurs without
significant fossae on any surface, features that do not exist in
non-ornithomimosaurs in combination with each other, or in connection to
the length of the first metacarpal exceeding 3/4 the length of the second
(rather, it is proportionately similar in length to *Gallimimus*').

  Barsbold originally proposed, in 1979 and later in 1983, as discussed
later by Norman in 1996, Molnar, Kurzanov and Dong in 1990, and Paul in
1988, that *Deinocheirus* and *Therizinosaurus* formed a monophyletic
association on the basis of long arms and large claws, despite the
evidence at the time of alternate arrangements based on more data.

  The most parsimonious association (for this worker, anyway) is that
*Deinocheirus* is what it seems to be, a VERY large ornithomimosaur, and
probably NOT a gracile one; but if one scales a *Gallimimus* to a
tyrannosaur allometry, in the hindlimb at least, one may arrive at a
higher mass and probably shorter length than recently proposed (by what
method this mass was arrived at I don't know).


Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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