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Re: Yixianosaurus (Theropoda) a basal paravian, not a basal maniraptoran (free pdf)



Raptorial Talon <raptorialtalon@gmail.com> wrote:

> Right, I was just referring specifically to your comment "Although the
> hands of certain non-avian maniraptorans have been
> described as being adapted for trunk climbing, none have feet adapted
> for grasping trunks." I guess I was thinking, or maybe wondering is
> more accurate, about whether the feet needed to *grasp* trunks in
> order to be considered "adapted" for climbing on them. I was thinking
> that perhaps (relatively) elongated toes and more hooked unguals could
> indicate a "bark-hooking" habit, so to speak, with grasping per se not
> being required. Obviously those traits still overlap a great deal with
> possible predatory functions . . .



Definitely.  Furthermore, the overlap to which you refer also provides
fertile ground for exaptation.


The specific issue I was alluding to is what if maniraptorans were
*limited* to trunk-climbing (as opposed to climbing around within the
canopy).  This might not be so bad in a Jurassic habitat, where many
of the columnar plants had few (if any) branches anyway - such as
bennettitaleans (e.g.,see
http://jasonbrougham.com/2013/09/23/bennettite-paleoenvironments/)
Plus, there was not much scope for the maniraptoran to linger in the
'crown' anyway.  So no requirement for perching or roosting.  But if
small maniraptorans were limited to trunk-climbing, I'm not clear what
the 'wings' were used for.  Arboreal mammals that launch themselves
from trunks require grasping feet in order to grip the substrate
(tree) and execute the launch impulse.


More generally, one of the issues that troubles me about proposed
arboreal scenarios for the origin of avian flight is the take-off
kinematics.  How did an arboreal quadruped with feet so poorly adapted
(if at all) for arboreality execute the take-off impulse?  This would
require the forelimbs to let go of the trunk or branch, so the animal
had to rely solely on the feet to remain in contact with the trunk or
branch, as part of this take-off phase.





Cheers

Tim