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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 <email@example.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
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
It has certain "advantages" -- being "previously tested" by bats and pterosaurs
>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
>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.
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