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Re: climbing dromaeosaurs and friends



----- Original Message -----
From: "Scott Hartman" <scott_hartman@hotmail.com>
To: <luisrey@ndirect.co.uk>; <gigi.babcock@alumni.usc.edu>;
<dinosaur@usc.edu>
Sent: Friday, December 08, 2000 2:25 AM
Subject: Re: climbing dromaeosaurs and friends


> Everybody,
>      The problem isn't simply whether or not maniraptorans could climb
trees.....


>      Of course it's fair to question whether perhaps some theropod limbs
> didn't operate in a parasagital plane; Larry Martin has suggested that
> Arcaheopteryx limbs were "monkey-like" in their articulation.  The utter
> lack of acceptance of this idea is evidence itseld...

Although I do not accept Larry Martin's reconstruction of Archaeopteryx,
let's not dismiss it just because it is unpopular--let's rely on evidence.

>  , but taphanomically it's
> also pretty unambiguous.  All of the Archeo specimens, despite their
myriad
> preservational positions, preserve the hind limbs in a parasagital plane
> (even when the forelimbs aren't).  Yet the far majority of articulated
> Solenhofen pterosaurs are preserved with the hind limbs in separate planes
> of articulation.  Clearly something functional is different between these
> taxa.

You are correct that there are functional differences, but that does not
necessarily prove your assertion!  Some years ago Wellnhofer argued
pterosaurs must have had sprawling hindlimbs precisely because many
specimens from Solnhofen have been found with the hindlimbs splayed out on
either side.  In my 1990 paper, I argued that this was not evidence that
pterosaurs could not bring their hindlimbs under their bodies to move in a
parasagittal plane and noted the following:

"Five of 18 specimens of Pterodactylus figured in the plates by
Wellnhofer (1970) in which the position of the femora can be
determined (Wellnhofer, 1970: Pl. 2, 4, figs. 1, 2, Pl. 6, 8),
have the femora preserved on one side like the bipedal
archosaurs."

So about 75% of Pterodactylus have their hindlimbs splayed out and 25% have

their hindlimbs preserved together in a more or less parasagittal plane.  I
argued that the fact that pterosaurs could have their hindlimbs preserved
both ways indicated that their hip joint was more mobile than that of
Archaeopteryx, and furhter that this was because in pterosaurs the hindlimb
was extended out in the plane of the wing and was involved in wing function.
I also suggested that the hindlimbs were more often splayed out, unlike
Archaeopteryx, because the wing membrane would tend to pull them out
laterally.

OK, what does the above and the position of the hindlimb in Archaeopteryx
tell us about hindlimb mobility in Archaeopteryx?  I suggest that it tells
us that the hindlimb was not as mobile as in pterosaurs, but this should not
be a surprise to anyone given an understanding of the morphology of its hip
joint.  I think it also tells us that the wing in Archaeopteryx was not
attached to the hindlimb in Archaeopteryx, which also should not be news to
anyone.  However, it does not tell us that the hindlimb of Archaeopteryx was
necessarily limited to move only in a parasagittal plane.  I think that the
hindlimb had to be able to move out of the plane (in all theropods) just as
it does in all sorts of extant animals who limbs normally move in a
parasagittal plane.

Chris



S. Christopher Bennett, Ph.D.
Asst. Prof. of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601-2449
cbennett@bridgeport.edu