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re: pterosaur femora sprawl
One thing that seems like a logic leap for me from the drawings of those who
advocate a quadrupedal stance in pterosaurs emphasizing the horizontal aspect
of the backbone is this: The hind limbs are portrayed as erect (dino-like) but
the fore limbs are portrayed as sprawling (very sprawling, often with the elbow
anterior to the glenoid-- see Bennett, Wellnhofer, Unwin, but exceptionally not
roboAnhanguera of Henderson working with Unwin). Under this scenario, is this
configuration viewed as phylogenetically unchanged since the pre-volant
quadrupedal ancestors?
Here's the alternate that makes more sense: As published in Peters 2000, 2002,
2007, I favor a bipedal pre-volant stage at which time the hands. freed from
locomotion, could have been locked into the pterosaur configuration of
producing laterally-oriented prints while maintaining a 30 degrees-out
orientation of the elbow. This is coupled with a Chlamydosaurus femoral
orientation customized with an extended ilium, more sacrals, smaller caudal
transverse processes, an improved femoral head, a tibia longer than the femur,
an improved ankle and less asymmetrical toes. Chlamydosaurus does have a wide
standing stance, but then it doesn't have a longer tibia than femur and the
rest of the above.
On the other hand, if continuously quadrupedal, then there had to have been a
series of taxa with an increasingly laterally-oriented manus (what would have
caused this??). And why would that have occurred on the road to dinosaurs or
dinosauromorphs since they were experimenting with bipedalism, little fingers
and digitigrady (Scleromochlus comes to mind)? And what's the new scenario?
You can't hang it on Wild's long-fingered lizard (basal diapsid) anymore (as
Bennett did at the Wellnhofer symposium). Too many archosaur synapomorphies
would have been already in place.
My other question is: Does the angle between the femoral head and shaft count
for any difference in standing configuration? There's wide variation in
pterosaurs (and other tetrapods for that matter) and I think the differences
should count. In all other tetrapods, the axes of the acetabulum and femoral
head align. Why should pterosaurs (whether flying or walking) merit an
exception?
David Peters
1247 Highland Terrace
St. Louis, MO 63117-1712
314-781-1795 phone and fax
314-323-7776 cell
davidpeters@att.net