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Re: dino-lice



2011/4/23 Tim Williams <tijawi@gmail.com>:
>
> Well then, now I see the problem.... *never* believe anything I say.    ;-)
>
He, sorry, my intention was not to suggest this... I think you were
right, and that this mobility, at least in supination, applies also
for forelimb involvement in hunting, according to work in
non-pinnipedian carnivoramorphans by Andersson and Werdeling (2003)
(Freely available at
http://rspb.royalsocietypublishing.org/content/270/Suppl_2/S163.full.pdf)
>
> It depends.  I wouldn't think grasping large prey requires much
> mobility at all, because the aim is to hold the prey in place.  Both
> forelimbs were used to hold the prey, on either side.  The trenchant
> unguals cut deep into the prey - and the prey's desperate struggles
> would just impale it further.
>
This looks reasonable. But, according to work on non pinnipedian
carnivoramorphans by the previously mentioned authors, the larger the
carnivore is, the most able to supinate it has to be. It is also
reasonable, because the proportionally greater stresses relative to
the capacity of resisting them (previously indicated by Michael Habib)
require greater adaptation, provided by some flexibility, to avoid
breakage in the struggle (in addition to adapting the holding limb to
the varying location of the prey body parts to be grasped). As you
indicated in the case of vermilinguans, carnivoramorphans also have to
manipulate the prey from different angles.

The fact that theropod forelimbs can be more retracted than protracted
are not quite suggestive of much use in predation (which would require
a forelimb more able to be protracted towards the prey), and getting a
prey too close to the chest may also put the theropod at risk of
receiving some blow (if the prey was relatively large). If the prey
was proportionaly small, as suggested by the study by Hone and Rauhut
on theropod predation, then the use of forelimbs to hold the prey is
less necessary, and the jaws would suffice.

In any case, I do not deny the involvement of forelimbs in predation,
but think there is no much unequivocal evidence for it. Large claws
may be alternatively used for intraspecific struggle, an important
function in kangaroos.

> For handling small prey, a grasping manus would certainly be an asset.
>  I don't think any maniraptoran was especially gifted when it came to
> grasping and manipulating small prey with the hands.  Not so much
> because of the forelimb feathers, but because the long, inflexible
> fingers were useless for this purpose.
>
Agree on this... but, conversely, in carnivoramorphans it is at small
sizes that less developed forelimb dexterity is most commonly present
(perhaps because they deal with proportionally smaller prey which may
need less manipulation), according the previously mentioned authors.

Cheers,

Augusto