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Re: Aw: RE: Arboreal Theropods: The prize at the bottom of the cracker jack box



Allan Edels <edels@msn.com> wrote:


> We have dromeosaurids which leave definite trackways showing their claws, and 
> many of them are what we
> would consider cursorial  - i.e. not quite arboreal.


Ummm.... not at all arboreal.


> Yet, I believe they have the ability to successfully grasp branches and hold 
> on, and possibly perch and/or
> roost in trees and bushes if needed.


One hypothesis is that branch-grasping abilities were not needed in
"tree-climbing" theropods, based on the nature of the prevailing
vegetation.  This is because at the time (Jurassic) large vegetation
was dominated by "cycadophytes", which tend(ed) to have columnar
trunks with few or no branches.  Thus, these sturdy plants offered no
real opportunities for perching or roosting, although they likely
offered food (nutritious fructifications) at the apex/crown.  So if a
small theropod was capable of trunk-climbing, that's all it needed.
No need to linger.  Cycads and bennetites provided poor shelter or
refuge anyway.


> I can imagine a _Deinonychus_ becoming trapped by a flash flood, and
> climbing whatever was nearby - rocks, trees, sauropods.  :)


Hungry dromaeosaurs might have climbed sauropods and large ornithopods
by choice - as part of a predation strategy against much larger prey.
I know there are no modern analogs for such behavior, but the pedal
digits appear to have have been used against (very?) large prey.  When
it comes to visualizing ancient predators, I much prefer digital to
analog.   ;-)


> It seems likely, that many of the theropods that have been in question in 
> this thread possessed the ability to
>  perch, roost, and climb into trees and bushes, prior to becoming paravians - 
> prior to actually flying.


But did this behavior actually lead to flying?


We can all agree that theropods gained the power of flight at some
stage.  We can also agree that theropods became arboreal at some
stage.  But did one lead to the other?  If so, which came first?
IMHO, the current evidence does not favor the "trees-down" model as
inherently superior.  A model that incorporates entirely terrestrial
behavior(s) as fostering the development of large aerodynamic wings
cannot be dismissed.


> Thereby, the need for a reversed hallux was not a requirement for these 
> paravians to be able to climb into
> trees and fly from them.


If these paravians climbed into trees, why did they need to fly from
them?  One hypothesis is that their arboreal abilities were so crap
that they were unable to climb down, so used their wings to return
them back to earth.  I'm willing to give this hypothesis a fair shake,
but I'm not sure how we'd go about testing it against the available
evidence.


All modern gliding mammals are arboreal specialists.  These critters
are arboreal quadrupeds, and gliding behavior came about as a
consequence of being specialized for a life in the trees.  Gliding
evolved as an efficient way to commute between trees, by bypassing the
ground.  IMHO, there is no evidence that theropods passed through a
tree-to-tree gliding phase.  So maybe a tree-to-earth gliding phase is
a plausible hypothesis...?  This hypothesis does not require paravians
to be fully arboreal.


I'd love to see a biomechanical study done on the forelimb of
_Confuciusornis_.  Was the weird (but very robust) manus adapted for
trunk-climbing?







Cheers

Tim