Re: Catch-22

[Tim Williams <tijawi@gmail.com>]

Don Ohmes <d_ohmes@yahoo.com> wrote:

> It follows that a "jumping-out-of-trees" evolution-of-flight scenario is not
> falsified by a perceived lack of "arboreal adaptations", given vertical
> climbing competence.


I'm inclined to agree with you here.  If vertical climbing competence
can be demonstrated for basal paravians, we have a ball game.


> So a conclusion that a wing-clawed vertical climber is/is not "arboreal" is
> interesting ecologically, but irrelevant in terms of "tree's down" vs
> "ground-up".


Agreed.  There is abundant evidence than no basal paravian was adept
in trees.  Dececchi & Larsson (2011) presented a strong case against
basal paravians being arboreal.  But IMHO the absence of arboreality
does not necessarily refute a "trees-down" origin of avian flight.


> Which might imply that the wing-clawed
> Archie/Archie-ancestors/Archie-siblings/ilks and sundry et als could ascend
> a tree stepwise more competently than the reverse process, which is
> descending stepwise -- as is typical in vertical climbers.


Again, agreed.  I'm convinced that basal paravians could not climb
*down* trees (e.g., see Dececchi & Larsson, 2011).  But was it the
need to get out of trees that provided the initial selection for
aerial behavior?


> Adopting as a working hypothesis that it did in reality both climb and sleep
> in trees, what evolutionary mechanism would change the pes beyond that seen
> in the fossil?


I suspect that sleeping in trees would favor the appearance of
branch-grasping/perching adaptations, in either the hands or the feet.
 The absence of said adaptations is why I'm so cold on the idea of
roosting behavior in basal paravians.






Cheers

Tim