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



As Mike has discussed before, slightly asymmetric =/= aerodynamically
asymmetric. In order to get aerodynamic benefits to asymmetry, ratios like
1.05:1 or 1.5:1 or 2:1 don't cut it. They are only "asymmetrical" in a
mathematical sense, not a biomechanical one.

On Thu, July 3, 2014 1:23 pm, don ohmes wrote:
>
> On Thu, Jul 3, 2014 10:41 AM EDT Mike Habib wrote:
>
>>However, I would argue that too much is being made of weather asymmetry.
>> There is nothing magical that happens when a feather is slightly
>> asymmetric. In fact, flightless birds often have asymmetric primaries,
>> they just are as asymmetric as in flying >species (on average).
>
> 1) asymmetric aerodynamic surfaces (more rigid/heavy on the leading half,
> lighter and more flexible on the trailing half) have evolved many times --
> eg, insects, airplanes, bats and birds. AFAIK, cross sectional symmetry in
> nature is limited to insects -- if it exists there.
>
> 2) if there is no advantage to a symmetrical primary (in extant flightless
> birds), why would an asymmetrical primary not be retained? The implied
> default drift-back-to-the-center tendency is likely non-existent, in the
> absence of selection moving the center of variance.
>
> 3) all the extant animals known to have asymmetric primaries are either
> volant, or have volant ancestors, again AFAIK...
>
> Discounting asymmetric feathers as a trait indicating at least the
> presence of volant ancestors seems overly something -- perhaps overly
> skeptical?
>


Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA