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David Marjanovic <firstname.lastname@example.org> wrote:
> These mammals are all quadrupeds. Their forelimbs are compromises between
> the hook-and-pull function and the locomotory function. Alvarezsaurids had
> no need to compromise, and it shows!
The giant pangolin (_Manis gigantea_) is mostly bipedal - and it still
has large forelimbs. Long forelimbs provide a longer reach.
Besides, most ant- and termite-eating mammals are quadrupeds because,
well, their ancestors were quadrupeds.
Augusto Haro <email@example.com> wrote:
> A problem I have with this hypothesis is that the extreme shortening
> and monodactyly separates these members from the condition in
> currently known large mammalian anteaters.
Here I agree with you. Here's what I wrote two years ago:
"If you're disturbing a nest of ants or termites, the last thing
you need is to have an army of tiny, angry, biting things
crawling all over you. Having your claws positioned so close
to your body, and your underside pressed right up against
the nest, seems like asking for trouble."
> In general, picking up prey actions also seem not so fitting with
> short forelimbs. In any case, the fused wrist bones suggests a poverty
> of manipulative action, and the ventrally facing palms do not seem
> good to grasp insects (better would look medially facing ones).
In the (entirely speculative) scenario of alvarezsaurs using their
forelimbs to help feed on lice etc, I envisioned the claws being used
to merely dislodge the parasite - not grasp it.
> It may be, although I suspect that dinosaurs with great olfactory
> acuity as tyrannosaurids and dromaeosaurids may reach it before and
> open the carcasses then. I would also expect more laterally compressed
> unguals, dromaeosaur-style, if expecting carcass hide-cutting.
> Besides, I do not see in the shout of alvarezsaurs much indication of
> carrion-eating, such as recurved beak or teeth...
The claws would be used simply to break open the outer surface -
whether skin or viscera. Besides, as Dann says, the narrow head
(especially in _Shuvuuia_) and long neck could be inserted into
available orifices, to gobble up the rotting flesh or viscera within.
It's not the most alluring of ecologies, but in today's world a lot of
animals do it, vultures being the most (in)famous example. Again to
paraphrase Dann, the forelimbs could take on an auxiliary function to
widen the orifice, or make a new one.
When it comes to feeding on a carcass, the alvarezsaurs might well
have been the last to arrive at the scene. Having high visual and/or
olfactory acuity may not have been so important, because (a) many
carcasses would have been huge and (b) alvarezsaurs could be your
typical camp-followers, and trailed larger predatory theropods with a
view to a kill.
I'm not suggesting that alvarezsaurs were obligate scavengers.
However, as noted by Longrich & Currie (2008), ant nests were likely
rare in the Mesozoic, and termitaria possibly absent altogether -
leaving wood-nesting termites as the only common social insect
contemporary with alvarezsaurs. So there would seem to be slim
pickings indeed for a theropod that relied solely on ants and termites
as its food source.