Re: Protoceratops Gender

["Rob Gay" <rob_redwing@hotmail.com>]

> do we actually KNOW which one is which? (i.e. Could the 
> small-bump-and-large-wide-frill specimens actually be the females?)  Has 
> anyone looked into chevrons at the base of the tail, or anything like that, 
> to try to determine the gender, like people were doing for 
> _Tyrannosaurus_?<
Part of the problem is that determining the presence of sexual dimorphism is 
devilishly tricky in the fossil record, and only a few dinosaurs meet the 
criteria in the first place (_Coelophysis_, _Allosaurus_, among theropods). 
But, even with a less than perfect sample size, you can still begin to make 
conclusions, provided you have at least a partial growth series. The 
question then becomes, to me, how many catalogued and described specimens of 
_Protoceratops_ are there?
And if sexual dimorphism is present, you would need a way to determine which 
morph corresponded to which sex (as you noted in the original e-mail). I'm 
not too familiar with ceratopsid paleobiology, but it would stand to reason 
that the larger frill would correspond to the male, for simple reasons of 
display. However, this may not be the case, and the bad part is that there 
really is no good way at all to tell which sex is which in the fossil 
record, except in very unusual circumstances (i.e. an icthyosaur giving 
birth). Some have suggested using chevrons, but there has turned out to be 
no real correlation there. Some have suggested using relative robustness, 
but this is equivocal, because robustness varries among genders, depending 
on the taxon. For dinosaurs, some have suggested that the pelvic opening 
that is wider was the female, because it would accomodate an egg. But, there 
is nothing saying that the large opening couldn't have been used to support 
the male sex organs. Unless you have an egg (which we don't have for most 
dinosaurs), this claim cannot be substantiated.
Conclusion (IMNSHO): You can determine if sexual dimorphism is present in 
the fossil record, but not which morph corresponds to which sex.
Peace,
Rob

Student of Geology
Northern Arizona University
Biological Science Tech
Manti-La Sal National Forest
AIM: TarryAGoat
http://www.geocities.com/elvisimposter/dinopics.html
http://www.cafepress.com/RobsDinos
"A _Coelophysis_ with feathers?"

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com