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Re: dino-lice

Augusto Haro <augustoharo@gmail.com> wrote:

> Nice speculation! What about the alvarezsaur using its forelimbs to
> clasp the large dinosaur, being carried by it while moving, and
> picking parasites around the fixed body? (we may also see the long
> hindlimbs as providing flea-like jumping, but looks like trying too
> hard a comparison with parasites). The retroverted pubes would help
> getting the center of gravity closer to the "host"'s hide, as in
> Chatterjee's arguments on proavians. Forelimb clasping may also help
> if only to get a free travel on a larger dinosaur, or avoiding the
> territory of some predator by passing above them (or being associated
> with a large powerful "host").

I was picturing a more mundane scenario, under which alvarezsaurs
picked the lice (and other parasites) off the hides of sauropods etc,
with their feet mostly on the ground.  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.  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).

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.  I
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).  Or as I suggested many moons ago,
alvarezsaurs might have been scavengers that used their strong,
monodactyl forelimbs to open up large dinosaur carcasses.

Alvarezsaurs could have been opportunists that targeted a variety of
food sources - insect-nests (including wood-nesting termites),
large-bodied hosts for parasites and/or blood, and carcasses for
carrion - whatever was around.  This would help explain the high
diversity and size variation seen in this clade.