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Asymmetrical feathers (was RE: Thoughts on the new Czerkas book (long))



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> James R. Cunningham
> Sent: Thursday, September 12, 2002 6:58 AM
> To: dinosaur@usc.edu
> Subject: Re: Thoughts on the new Czerkas book (long)
>
> Why is the assumption often made that lack of assymetry in
> ancient feathers is a
> non-volant indicator?

Actually, it's sort of the other way around here.  Czerkas et al. cite
feather asymmetry as evidence for the volancy of Cryptovolans.  I was
pointing out that their claim of asymmetry is unjustfied for the few
feathers they figure for which the margins and shaft are all clearly
visible.  As you point out, symmetrical feathers doesn't mean that it
couldn't fly!  However, they have not justified their claim of feather
asymmetry (regardless of the implications).

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> longrich@alumni.princeton.edu
>
>       Feather symmetry is a pretty complicated issue, for one volant
> birds do have relatively symmetrical remiges and retrices in the inner
> retrices and secondaries. Outer, and especially leading edge, feathers
> tend to be where asymmetry is most pronounced.

Quite so!!

> Second there's the
> measuring question. I'm still baffled as to how anyone can accurately
> get measurements on the Berlin Specimen of Archaeopteryx considering
> that the feathers overlap each other, with the leading edge of each vane
> overlapping the trailing edge of the next (as in modern birds). Other
> than perhaps the separated tips of a couple of primaries, these
> measurements just can't be done as far as I can tell.

Definitely agree.  In fact, I had problems finding feathers in their
illustrations for which both margins and the main shaft were simultaneously
visible.

> So (not having the
> book myself) my question is- are these inner or outer feathers, and are
> they separated or are the vanes overlapping each other?

Truth be known, the only feathers which are clear enough to measure on the
type (where the margins and shaft are both clear) are the patch near the
leg.  I suspect that the Czerkas interpretation is that these are the outer
feathers of the arm; however, I argue that these are leg feathers, for
reasons cited earlier in this thread.

The best preserved feathers of the referred specimen (LPM 0159) are also
found near the legs, but at least some of these are displaced (they do not
align with the bones of any limb or the tail.  However, close up of these
(Fig. 18) indicates that most of these are not fully prepared out the
sediment (there is a slight overlap of a lamina of sediment along at least
one, and sometimes both, margins), so calculating symmetry on these are
difficult.  The only one fully prepared up is the lowest one on Fig. 18, and
is highly symmetrical in shape (but the shaft is not clear).

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796