Re: Archaeopteryx feathers and origin of flight based on 11th specimen

[Mike Habib <biologyinmotion@gmail.com>]

In addition, it isn’t altogether clear that the “resting state” for feathers of 
the limbs is symmetry - when tarsal feathers are induced in chicken models, the 
distal ones are often slightly asymmetric. The genetics of feather asymmetry 
also turn out to involve fewer loci than expected (based on work by Cheng-Ming 
Chuong and colleagues). So it may be that the earliest primaries were already 
somewhat asymmetric, and that variation was relative extensive. (In fact, there 
is a great deal of variation in feather asymmetry within living flying birds).

—Mike


On Jul 4, 2014, at 9:32 AM, Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:

> I slight asymmetry is functionally no different than symmetry, there is no
> positive selection for *symmetry*, either.
> 
> And slight asymmetry may help with the maintenance of feather curvature,
> with imbrication when the wing is formed, etc.
> 
> On Fri, July 4, 2014 3:22 am, Martin Baeker wrote:
>>> Yes, the structural spar tends to sit closer to the leading edge
>>> than the trailing edge of the wing. The mechanical importance of
>>> this for bending and torsional resistance is well understood, and it
>>> does not apply if the leading edge is only slightly shorter than the
>>> trailing surface.
>> 
>> If this is so, what other advantage does asymmetry have? For if
>> there were no advantage to a slightly asymmetric feather, it seems
>> difficult to envison the evolutionary path to full asymmetry. (And
>> no, I dont accept "display function" as an answer here :-)  )
>> 
>> Martin