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Gender (was:Re: [Re: Sue(was: Running T. rex)])



On 24 Dec 00 15:00:54 EST  
 archosaur wrote:
>I thought that the first chevron criteria was a good one. It was logical from
>a biomechanical point of view and we had close dinosaur relatives that shared
>it. 
>
>Unfortunately this now appears to be dubious. The missing first chevron has
>apparently been found, which would make Sue male.
>
>Incidentally I do have a question for Chris. I apologize in advance if you
>didn't want this on the list, but it came to me now after reading the previous
>e-mail.
>
>You had stated something about not being able to reproduce the first chevron
>results in crocodylians. Why exactly is this? Shouldn't this be a simple
>matter of X-raying some living crocodiles (and if the money allows it, why not
>do all 23 species) to see how it holds up. 
>
>Or has that already been done and this is the reason for the doubt?

I don't buy the chevron argument.  Sure, the crocodylians are close relatives 
of the dinosaurs, but that doesn't necessarily mean anything.  There are other 
close dinosaur relatives that do not possess the chevron differences, as is 
true with dinosaur descendants.

I like the morphotype idea much more.  Raath's (1990) work on Syntarsus, which 
appeared in Currie and Carpenter's volume _Dinosaur Systematics_, may be the 
best look at different morphotypes in the same gender.  By studying more than 
30 Syntarsus individuals, Raath concluded that there were two distinct body 
types-robust and gracile.  Furthermore, he concluded that the more robust form 
was female.  

In the same volume, Carpenter independently suggested that the more robust form 
was female.  However, he specifically looked at Tyrannosaurus rex individuals.  
This is more iffy, as 1) there are nowhere near enough T. rex individuals to 
conduct an accurate study (imagine conducting a Presidential poll by only 
talking to eight or ten voters 2) and the T. rex specimens he used were from a 
variety of different locations.  Raath's Syntarsus specimens were all from the 
same deathbed assemblage, meaning that it was more than likely that they were 
members of the same community.  

Regardless, I like the morphotype idea better than the chevron argument because 
the morph studies use the dinosaur fossils themselves, not relatives such as 
crocodiles.  

However, I don't think that there is a conclusive way to really tell the gender 
of a fossil specimen, unless, of course, it is fossilized giving birth, much 
like that famous Holtzmaden Ichthyosaur is.  

Just curious...does the chevron argument hold up in any living animals other 
than crocodylians?

Have a Merry Christmas!

Steve


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Steve Brusatte-DINO LAND PALEONTOLOGY
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