re: pterosaur femora sprawl

[David Peters <davidpeters@att.net>]

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