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Re: Walking with Dinos



-----Original Message-----
From: James R. Cunningham <jrccea@bellsouth.net>
To: dbensen@gotnet.net <dbensen@gotnet.net>; dinosaur@usc.edu
<dinosaur@usc.edu>
Date: Wednesday, October 06, 1999 2:43 PM
Subject: Re: Walking with Dinos


>
>
>dbensen wrote:
>
>> I think they could
>> have done better if they had paid some attention to the extant animals
they were
>> imitating.
>
>I agree.
>
>>  If they had digitized bird flight, for instance, and then plugged that
>> into the pterosaurs, it would have made them more convincing.
>
>No it wouldn't.  Pterosaur wing membranes don't carry stress in the same
manner that
>bird feathers do, the wrist and wing finger pivot don't articulate along
the same paths
>as birds,

...not according to Padian "Flying and walking in pterosaurs" pg
227...(reffering to the wrist in birds and the wing-finger loint in
pterosaurs)..."...in birds and pterosaurs the bones forming this
articulation have been fused and modified into pully-like hinges with a wide
arc of movement possible in only one plane."


> and the flapping oscillation is powered by different muscle orientations.


Again,...from the same source (pg 225),..."Pterosaurs lack a foramen
triosseum because they have no clavicles, but they do have a groove on the
medial face of the coracoid that outlines the path of this tendon......and
indicates that the original depressor function of the supracoracoideus was
reversed, as it is in birds. The origin of this muscle is expected to have
been along the midline of the sternum on both sides of the keel, as in
birds. Its tendenous insertion is indicated by a distinct rugosity on the
greater tuberosity of the humeral head in pterosaurs."  To me this says that
this particular major flight muscle DID have the same alignment in both
birds and pterosaurs.


 > A flapping pterosaur wing would not look at all like a flapping bird
wing, though the
>gross motions are each reminiscent of the other.  Even when soaring, the
bird and
>pterosaur load paths are different.
>


I don`t know an extremely lot about flight mechanics, but do think (from
what I have read, that these mechanics were similar for both small birds and
small pterosaurs. After pterosaurs evolved into larger forms, they may have
adopted structures more related to long distance soaring rather than
flapping flight. Again,...I`m still trying to learn this subject, so, if you
can recommend some "refs" on this subject (especially some more
recent...post 93 ones, I`d appreciate them...8^). Sincerely,...Larry F.