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Re: Yet more on pterosaur quad arm posture



Rescued from truncation:

From: Mike Habib <biologyinmotion@gmail.com>
To: "GSP1954@aol.com" <GSP1954@aol.com>, Mark Witton <Mark.Witton@port.ac.uk>
Cc: "dinosaur@usc.edu" <dinosaur@usc.edu>
Subject: Re: Yet more on pterosaur quad arm posture

I received a message that my note below did not make it through
previously, so here is another shot (relevant with Greg's follow up):

It is also worth keeping in mind Fujiwara and Hutchison (2012) which
recovered evidence for parasagittal limb posture in Anhanguera, using
morphology alone:
http://rspb.royalsocietypublishing.org/content/early/2012/02/17/rspb.2012.0190.abstract

With regards to limb positions during flight:

- Birds do not hold their forelimbs in the skeletal minimum drag
position during flight.  It's close, but not quite there.  Also, while
plenty of motion does occur at the elbow, tracking work in pigeons etc
show plenty of depression at the shoulder, as well.  Greg is correct
that you might not predict this from the skeleton alone, but
ultimately wing depression at the shoulder in birds is important.
Wing elevation involves even greater shoulder excursion (see, for
example:http://jeb.biologists.org/content/213/10/1651.full)

- For pterosaurs, there is no way to get the wing into a position that
is consistent with articular surfaces, plausible for flapping flight,
and also a low drag configuration with regards to the wing skeleton.
In practice, the wing skeleton was probably held in a position that
would present a high drag profile inboard (not so bad distally) if
soft tissue was not present.  In reality, of course, the lowest drag
profile for the wing is not necessarily the same as for the skeleton
alone, and there was likely significant faring around the wing spar in
pterosaurs from muscle, adipose, and air sacs.  For the elbow, this
would require something of a nacelle to form, for which there is some
circumstantial evidence, but nothing concrete to date.  The
alternative, of course, is that pterosaurs simply dealt with some
extra drag on the wing, which is also quite plausible.

--Mike


Sent from my Cybernetic Symbiote

On Jun 30, 2013, at 7:30 PM, GSP1954@aol.com wrote:

> In a message dated 6/27/13 3:26:25 AM, mark.witton@port.ac.uk writes:
>
> << Pterodactyloid trackways show that their limbs are held in parasagittal=

[ rest of quote elided -- MPR ]