RE: 2nd toe (was Jeholornis)

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Dan Bensen wrote:

> First of all, is the hyperextendable second toe a feature shared by
> related bird groups?

Good question.  As I mentioned, there is a minority view that
_Archaeopteryx_'s second toe was hyperextendible.  If true, this raises the
question of whether it's an incipient feature that pre-dated the
sickle-claw, or was retained after secondary loss of the sickle-claw.  

I've also heard that _Patagopteryx_ has this feature (can anyone confirm -
Mickey M.?).  _Rahonavis_ certainly does, in conjunction with that
formidable sickle-claw.  This feature may or not be present in _Jeholornis_
- this isn't mentioned in the text (I'll check the Suppl. Info.).

> Secondly, perhaps the toe's function was as a climbing aid.  Fingered
> birds lacked alulas, (or is it alulae?) and so wouldn't be as good at
> fluttering around in trees.  Climbing, with the aid of piton-like claws 
> on the feet and hands, might have been very useful.

The alula prevents 'stalling' during slow flight, by forming a slot that
directs air over the wings - useful in preventing crash landings.  Its
presence or absence probably had little effect on fluttering between trees.


The notion that the sickle-claw served as a climbing aid is intuitively
attractive, and has mentioned on the list and in the published literature -
including _DA_.  Modern seriemas have been reported to use their enlarged
inner toe-claws (which are not hyperextensible, however) in climbing trees.

Seriemas are darn cool!



Tim


------------------------------------------------------------ 

Timothy J. Williams, Ph.D. 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 9359