Re: sickle-claws

[Tim Williams <twilliams_alpha@hotmail.com>]

Jaime A. Headden wrote:

>   Actually, they are probably correct in applying limb-based strategies in
> engaging prey or carcasses. It has been stressed elsewhere that the power 
> of
> the arms in engaging a target are not neccessarily in the hands, which were 
> not
> just gracile but acted with the second and third digits in a single unit 
> (see
> Gishlick's work),

Yes, it is Gishlick's hypothesis that _Deinonychus_ and other dromaeosaurs 
grabbed and held prey in a two-handed fashion.  Alone, one hand had limited 
use in grabbing or holding.  This makes sense if the prey was large - the 
predator could sieze the prey using its forelimbs like a pair of ice tongs 
(where, similarly, most of the strength emanates from the base of the tongs, 
not the two ends).  It makes less sense if the predator targeted small prey, 
especially given the long, stiff fingers (with feathers attached in some 
forms).

> but also that the wrist was restricted in mobility as was the elbow 
> (Gishlick again, but also see Paul's own work).

The semilunate carpal joint certainly limited the mobility of the wrist in 
one direction, but it increased the range of movement in the other (the arc 
over which the wrist 'swivelled').  The idea that the elbow also had limited 
mobility is more controversial.

Roberto Takata wrote:

> > Seriemas (which can fly, and are predominantly terrestrial) are reported 
> to
> > use their enlarged inner claws as climbing aids.
>
> Did the _Deinonychus_ anatomy allow them to climb a vertical surface?

Just a point in clarification.  As I understand it, the sickle-claws of 
seriemas are not used to help climb vertical surfaces (like trunks).  
Rather, they appear to play a role in helping the birds clamber over 
vegetation - although I'm hazy on the details.

> Though the climbing claw hypothesis is compatible with Kenneth P. Dial
> (2003) hypothesis for the flight origin:
>
> http://www.sciencemag.org/cgi/content/full/299/5605/329
> http://www.sciencemag.org/cgi/content/full/299/5605/402

Yes, glad you noticed that.  :-)

Cheers

Tim