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Re: Triassic archosaur bipedality and cursoriality



Tim,

Fair enough, what you wrote was "don't appear to have been terribly useful" so my restating of that was inaccurate. Nevertheless, I suspect they were still of more use than that. As for carnotaurines, Carnotaurus has, as I recall, a rather large ungual on the manus, which to me looks like it might well have had some function. Has anyone looked at how forelimbs become reduced and lost in vertebrates, i.e. are there patterns of reductions (such as reduction and loss of unguals before reduction and loss of rest of digit, etc.) that might be of predictive value when looking at things such as the odd forelimbs of carnotaurines or alvarezsaurids? If we can discount that the limbs are being reduced, rather than dramatically specialized, that would be a good starting point for discussions and investigation.

Dan


On 7/1/2012 6:48 PM, Tim Williams wrote:
Dan Chure <danchure@easilink.com> wrote:

The comments about the forelimbs of many non-avian theropods being of not
much use might just be a wee bit premature.  Many of them have stout arms,
fingers, and claws with marked muscle attachment scars and  well developed
deltopectoral crests.

Agreed.  I'm not saying that the forelimbs of all theropods were
*useless*.  Not at all.  I'm merely saying that the role of the
forelimb was typically less useful than previously assumed.  Initial
prey capture seems to have been carried out by the jaws, with the
forelimbs (if used at all) then used to grapple with the prey, and
keep it secure.  The range of motion of the forelimbs, especially
their reach, seems to have precluded a role in catching prey.  I agree
that in many theropods the robust (although often quite short)
forelimbs tipped with trenchant unguals meant that there were still
important in handling prey (once caught).


Yes, carnotaurines have weird forelimbs, but they are
not sunk into oblivion.  I suspect they had a specialized function we can't
now, and maybe never will, be able to discern.

I'm not so sure about that, Dan.  The extreme truncation of the distal
forelimb, plus the reduced innervation, strongly suggests that the
forelimbs of carnotaurines were non-functional.  For tyrannosaurids,
I'm willing to believe that the diminutive forelimbs retained some
predatory function, such as to help hold struggling prey (very large
prey, in this case) while the teeth went to town on the prey.







Cheers

Tim



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