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Re: Deinonychus claw use and origin of flapping

Denver Fowler <df9465@yahoo.co.uk> wrote:

> 3. The ability to do something is not the same as selecting for it.
> I agree that little theropods may have been able to climb trees, but the 
> ability to perform an action is not the same as having a
> selectable pathway by which morphology can be changed.

Agreed, 100%.  For small paravians, it all hinges on whether certain
changes at the extremities were related to climbing or not.

> I remain skeptical about arboreal / scansorial adaptations or habits in these 
> small theropods, especially regarding the
> subarctometatarsalian metatarsus of the basal deinonychosaurians. This is a 
> cursorial adaptation, so why it would be selected for
> in an arboreal animal is currently unexplained.

Two things:

(1) If a small theropod divided its time between the land and the
trees, it might still retain or acquire cursorial abilities for the
terrestrial part of a "dual-mode" ecology.  This would be especially
true of a small paravian that spent most of its time on the ground,
and only occasionally ventured up or into trees.

(2) It's my understanding that the "wedge-and-buttress"
arctometatarsalian condition (and the less derived
subarctometatarsalian condition) is tied to the transmission of forces
up and down the distal hindlimb during foot-fall. It offered
advantages to highly cursorial animals (Holtz, 1994).  But I wonder if
it might also be advantageous to animals descending to the ground from
height (such as leaping or gliding out of trees), to help cushion the
impact of landing.  I just came up with this notion off the top off my
head, and I'd be more than happy to be wrong here.