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2011/4/17 Tim Williams <email@example.com>:
> There might have been some
> clambering (hindlimbs only) by the alvarezsaur over the host, while
> the host was resting or lying down... but without the alvarezsaurs
> themselves being ectoparasitic.
I do not necessarily say that they were... just that they may have
attached to the host (and perhaps picking ectoparasites while
attached). I do not know if the term is commensalism or parasitism for
pseudoscorpions using harvestmen as transport. Perhaps it may be
parasitism, because carrying another animal may imply an extra effort
the other animal is not expending.
> In other words, when the host got up,
> the alvarezsaur got off. The short, stubby forelimbs of alvarezsaurs
> were useless for grasping, or for using as crampons (as proposed by
> Manning &c for dromaeosaur claws, for example).
I was thinking in forelimbs being used to hook, just to fix to
vertebrates, not climbing crampon-wise, nor grasping with one hand
alone. I thought perhaps both their shortness and robustness are well
designed for the forelimb bones to resist the shearing forces
generated by the weight of the alvarezsaur (the shortest a stick is
maintaining the same width, the more difficult to break). The powerful
muscular attachments indicate relatively thick bones which would help
in the tensile, principally tonic effort of maintaining the grasp.
> Senter (2005) proposed on biomechanical grounds that the forelimbs of
> _Mononykus_ were well adapted to scratch-digging or hook-and-pull
> movements, and so proposed that alvarezsaurs used their findlimbs to
> open tough insect nests, in the manner of anteaters and pangolins.
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.
> don't mean to contradict this - but it's possible that the alvarezsaur
> forelimb morphology lent itself to other functions too. Such as
> picking off parasites from large hosts - or cutting through the same
> host's skin as well for a blood-meal (as seems to be the case for
> oxpeckers on ungulate hosts).
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).
> Or as I suggested many moons ago,
> alvarezsaurs might have been scavengers that used their strong,
> monodactyl forelimbs to open up large dinosaur carcasses.
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...
I was also thinking in a pecking animal which turned rocks around as
bears do to uncover small arthropods. But, of course, comparison with
the long-limbed bears does not show many similarities. In any case, it
seems to me a alvarezsaurid forearms, because of their unique design,
may have been used in quite an unique way among vertebrates.