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Re: dino-lice



Jason Brougham <jaseb@amnh.org> wrote:

> Can you name one extant vertebrate that has undergone an extreme reduction of 
> a limb or any other body part in its evolutionary lineage, in which that body 
> part played an important role in feeding?


Define "important"?  BTW, I'm not actually saying that the forelimbs
of alvarezsaurids played a *major* role in feeding - just some kind of
role.  I don't know what.  But the heavy-duty musculature indicates
the forelimbs were capable of applying a hefty force for some reason.


Off-hand, I can't name an extant vertebrate that fits your criteria.
In any case, your question may well be inapt because (aside from
birds) most extant vertebrates are quadrupeds of some description.
Late Cretaceous alvarezsaurids evolved from bipeds that used their
hands for predation (i.e., a trophic function), not for locomotion.


> In other words, when a lineage of animals undergoes extreme reduction in a 
>  body part, isn't that body part usually becoming LESS pivotal in survival 
> rather than more?


Yes, probably.  That doesn't mean that the particular structure is
useless, or vestigial.  Look at the forelimbs of tyrannosaurids -
tiny, but they might have been important in acting as 'meat hooks' to
grapple with large prey.  Thus, the diminution of the forelimbs
reflects a reduced role in predation (in contrast to a more important
role for the head), but according to this hypothesis the tiny
forelimbs retained a trophic function.  This is the kind of situation
I propose for the abbreviated forelimbs of derived alvarezsaurs -
although without the specifics of tyrannosaurids.  (I don't for one
moment suggest that derived alvaresaurs used their forelimbs in
predation!)




Cheers

Tim