Re: Feather Flap

[Tim Williams <twilliams_alpha@hotmail.com>]

Michael Habib wrote:

> Which brings up the question of what characteristics we actually associate 
> with arboreality in birds (and/or near-bird theropods).  The reversed, 
> gripping hallux is obviously a distinctive characteristic when it appears, 
> but I don't think we should be overly reliant on that character (it is also 
> worth pointing out that a reversed hallux does not always indicate arboreal 
> habits: the animal could also be secondarily terrestrial, as in 
> roadrunners).

Well said.  This was a point I was alluding to previously with _Gansus_ - a 
shorebird (webbed feet, &c) with a reversed hallux, but probably weak 
perching ability on account of the short hallux.

>    For one thing, the theropods in question may have been able to climb 
> somewhat quadrapedally.  That changes the mechanics of climbing enough that 
> the correlation between arboreal habits and hallux morphology may be looser 
> than we expect.

I agree completely.  The problem is trying to frame an ecomorphological 
model for climbing in theropods that can be "tested".   Something along the 
lines of biomechanical studies combined with modern analogs - such as what 
was done with the study of _Mononykus_'s forelimbs in a fairly recent study.

> In addition, while tight gripping of branches is quite helpful and 
> important for modern arboreal birds, I am not convinced that it is required 
> for an arboreal existence (especially in animals with powered flight or 
> extensive gliding ability).

I'm very sure that tight gripping of branches is not required for an 
arboreal existence.  For example, at least one species of "flying squirrel" 
(from Japan) has very stiff manual and pedal digits.  It can't grasp tree 
branches very well, but apparently it's excellent at climbing trunks.  Then 
again, as a squirrel, it does have quite mobile wrist and ankles - something 
that theropods do *not* have.

> One set of characters of note in the regard are actually structural 
> characters: extant arboreal birds (including modern passerines and 
> falconimorphs, for example) seem to fall within a similar range for certain 
> quantitative, structural characters associated with limb loading.

That sounds very interesting.  Do you have a particular study in mind?

Cheers

Tim

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