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Re: Triassic archosaur bipedality and cursoriality

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.