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Re: Parasaurolophus



 From: ornstn@hookup.net (Ronald Orenstein)
 > 
 > >Given that sort of a bimodal distribution of morphs in a *single*
 > >species, the only reasonable conclusion is sexual dimorphism.
 > >Under those circumstances, it is almost always the male that is
 > >more gaudy - more display oriented.  Ergo, the large-crested forms
 > >are males.
 > >
 > >swf@elsegundoca.attgis.com          sarima@netcom.com
 > 
 > Maybe.  But female cassowaries happen to have larger casques than males and
 > to be larger and more brightly-coloured overall, so we can't claim that we
 > know for sure what the story was in hadrosaurs. 

The cassowary is an isolated example.  As far as I know it is not part
of a larger taxonimic group characterized by female display.

The fact that sex-differentiated display structures are present
across several genera of hadrosaurs makes it *far* less likely
that the display-prominant individuals were female.  Thus the
cumulative evidence from the larger group indicates prominant males.

[Note, the case in Parasaurolphus is far from solid, given the
wide seperation of the "short-crested" specimen from the long-
crested ones].

 >  Admittedly if the crest is
 > indeed a sound-producing organ (which it certainly is not in cassowaries)
 > that may, on comparison with living forms, make it more likely that the
 > larger animals are males, as I can't think offhand of a living tetrapod in
> 
I find the evidence for this rather strong.  I see no other really
likely explanation for the nasal passages entering the crests.

Note, they must be visual display structures as well, since the shape
differences exceed the differences necessary to produce distinct
sounds.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.