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Re: [dinosaur] Serikornis, new Jurassic theropod from China with transitional feathers



David Marjanovic <david.marjanovic@gmx.at> wrote:

>> "[...] However, the manual digits of _Serikornis_ are long
>> and slender with strongly curved unguals I and III. This supposed
>> that they could have been effective for climbing trees as
>> in _Archaeopteryx_ (Feduccia 1993; Manning et al. 2009;
>> Wellnhofer 2009). In this way, the hindlimbs can be regarded
>> as less specialized than the forelimbs for grasping."
>
> For grasping what?


Yes, that was my question.  If the hands were capable of grasping,
they would presumably only be capable of grasping (relatively) large
objects using both hands at once.  For pennaraptorans (_Serikornis_
included) the manus was likely incapable of grasping small objects -
branches, fruit, small prey, their own eggs, etc.  First, there is the
lack of prehension by the hand - especially if two fingers were bound
together.  Second, long forelimb feathers would inhibit the ability of
the hand to grasp small objects beneath the animal (because the wing
would smack into the ground) or to clutch small objects above the
ground with both hands (because the paired wings would collide with
each other).  Neither is a problem for grasping large objects, but
both constraints would make grasping small objects extremely difficult
- either with one hand or both hands.

To be brutally honest, I'm not sure why many pennaraptorans had clawed
hands at all.  They appear to be utterly useless for climbing (except
maybe trunk-climbing), and of limited use for predation (except for
grasping large prey).  I'm beginning to think that hand-claws were
retained for close-range intraspecific combat, or maybe defense
against predators - like the wing-spurs of certain extant birds
(screamers, plovers/lapwings, jacanas, etc).  If feathered wings
initially evolved for display purposes, maybe the wing-claws of basal
pennaraptorans added a threat component?  Again there are parallels in
modern birds.



> Prey rather than branches, I think. Just yesterday I got to see a little 
> tyrannosaur skeleton with finger claws like an eagle's toe claws, but much 
> less curved toe claws.

For tyrannosaurs I would guess that the jaws did all the heavy lifting
(including literally).