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gender determination in pteros?



Chris Bennett has given us a hypothesis on gender determination in Pteranodon. 
He showed  that a mid-size pterosaur pelvis (KUVP 993) was much more open 
posteriorly than one of the largest known pelvises (pelvi?) (and twice as big 
as KUVP 993), the type of P. ingens YPM 1715. Unfortunately some of this 
openness comes from missing material -- still, reconstructed, it is more open, 
relatively and in reality, than the larger specimen. 

Does this mean that females were smaller overall, but had a wider pelvic 
opening? That's possible.

I wonder if, considering the increased number of incorporated sacrals in YPM 
1715 (again possibly due to post-mortem damage in KUVP 993), that a larger size 
might simply result in more ossification -- larger areas for muscle anchors. In 
this scenario, the opening in YPM 1715, although relatively alot smaller and 
really just a little smaller, is still large enough to pass a neonate. Unlike 
most pterosaurs, the ischia are fused medially in Pteranodon, so the ischia 
cannot spread ventrally to allow passage -- if they ever did so. Most of the 
increase in 1715 seems to broaden the pelvis anteroposteriorly, where the 
muscles attach. 

Phylogenetically, pterosaur pelves and especially ischium shapes in pterosaurs, 
have wide morphological variation. Many are widely separated from the pubis and 
some ischia may be so narrow they could almost be described as paddle-like. 
These shapes follow phylogenetic patterns. I don't see mixes, as in gender 
differences, within clades. And I don't see ontogenetic differences, as 
Wellnhofer suggested for Rhamphorhynchoid pelves in 1975. 

Anyway, this issue may not be settled yet. As I understand it, KUVP 993 may 
have been found isolated and disassociated from other skeletal material. That's 
unfortunate and could have added much to the story, either way. The pelvis on 
YPM 1715 is quite similar to a much smaller pelvis, the Triebold specimen, that 
comes from a virtually complete pterosaur which has only a short (no longer 
than the skull is deep) crest preserved. It has a male-type pelvic opening and 
a female-type crest. Or does it?

More later,

David Peters
St. Louis