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Jason Brougham <firstname.lastname@example.org> wrote:
>> I like the idea that the single-clawed forelimbs of alvarezsaurs were
>> used to penetrate carcasses (especially from the inside), or that they
>> were used to prise parasites off hides - either from the hides of
>> other species, or from each other (as a grooming tool). Thus
>> returning us to the origin of this thread: Dino-lice.
> Those functions do not explain the limb shortening trend in the group.
> Both jobs could be accomplished better with unmodified, primitive, arms.
I agree. But as I said in a previous post, I believe the truncation
of the alvarezsaurid forelimbs was associated with the forelimbs not
being used all that often and/or reflected a reduced role in feeding.
After all, the tiny forelimbs of tyrannosaurids could have been used
to help secure large prey - but obviously this role would have been
accomplished better with longer arms (as with _Acrocanthosaurus_).
This is the point I'm trying to get across: the role of the reduced
tyrannosaurid forelimbs was altered, even though it retained its
ancestral predatory function (helping to secure prey). Why couldn't
the reduction of the alvarezsaurid fuorelimb followed a similar theme?
The forelimbs retained their ancestral function (such as scavenging,
or digging, or grooming), but shrunk in length to reflect their lesser
importance to the animal's overall ecology. Your statement that a
task "could be accomplished better with unmodified, primitive, arms"
overlooks the fact that the length of the forelimbs can decrease as
part of a modified feeding strategy.
The apparently atrophied forelimbs of carnotaurines represent the
extreme end of the spectrum. But they didn't become useless
overnight. In the transition from long forelimbs that had an
important role in prey handling (like _Ceratosaurus_) to being utterly
useless (like _Carnotaurus_) the forelimbs probably passed through a
phase where they had a limited role in predation. During this phase,
they got smaller.