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Re: something interesting I didn't know



>I noticed that the big ungual on digit II of a male cassowary, 
>_Casuarius unappendiculatus_, was something like 20% longer than on a 
>similarly sized foot of a female of the same species. The horny claw 
>on digit II on a study skin of a male of _C. bennetti_, and also a 
>male of _C. unappendiculatus_, looked positively enormous.

>I don't remember seeing anything in the published literature about 
>possible sexual dimorphism in the nasty digit II claw of cassowaries. 
>Does anybody out there know if such sexual dimorphism has in fact >been 
documented in these birds?  If it does occur, one irrestibly >starts 
wondering about the possibility of sexual dimorphism in the >digit II 
slicer of dromaeosaurids or troodontids.

I think ratites are a very good place to start when discussion sexual 
dimorphism when relating to dinosaurs, as these are the closest living 
birds to dinosaurs.

When it comes to telling sex in dinosaurs, there are two places one 
could look that is immediately evident: the pelvis and anterior 
chevrons.

1) the wideness of the ilia might suggest whether there was a birth    
canal or not. Of course, passing eggs or live young (viviparousness    
or oviviviparousness) would depend on finding empryos within    theropod 
(or any dinosaur) skeleton that we can conclusively say    wasn't eaten 
or eggs with clear indication that the embryos are of    the adult 
dinosaur specified.

2) I noted a while back that *Tyrannosaurus* had two types of ischia,    
one narrow and strutlike, the tip bent down and in, and the other    
straiter with a little knob at the end. Since then, I've seen the    
same variation on *Composgnathus* (the German specimen has the       
knob, while the French one lacks it). This could even be sub-    
speciate designation; the knob-less skeletons seem to be larger    
(female?) and more gracile than the knobbed, robust ones (males?).

3) the crocodile has two morphs for the anteriormost chevron [Horner's    
_the Complete T. rex_] long for the male, and short for the female.    
We cannot look to birds for this indication, since no living bird     
(and most extinct ones) has chevrons.

If I missed any points, e-mail me, but if you disagree . . . oh well, 
e-mail me, too. I welcome the commentary.

Jaime A. Headden

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