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




On Wed, Jul 24, 2013 12:50 AM EDT Tim Williams wrote:

>Allan Edels <edels@msn.com> wrote:

> 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.

Generally speaking, and excluding the terminal branch environment, the talent 
required to claw-climb a vertical trunk will provide access to the entire 
near-trunk environment. This would include the apex
of cycad or palm forms, unless the fronds are too dense to allow passage -- 
which would seem unlikely in a small animal.

When you say "poor shelter", are you referring to weather? 

>IMHO, the current evidence does not favor the "trees-down" model as
>inherently superior.  

It has certain "advantages" -- being "previously tested" by bats and pterosaurs 
being one. 

>A model that incorporates entirely terrestrial
>behavior(s) as fostering the development of large aerodynamic wings
>cannot be dismissed.

Agreed. Or a mix -- I know of no proposed terrestrial model that can't be 
incorporated into a roosting lifestyle, for example.

>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. 

Cats climb up more easily than down -- it is inherent to claw-climbing. 

>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.  

Agreed.

>So maybe a tree-to-earth gliding phase is
>a plausible hypothesis...?  This hypothesis does not require paravians
>to be fully arboreal.

Yeah, good point.

>
>
>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