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

Note: I have already read Chris's response and agree that if the placement is
so variable between extant taxa then it might be best to leave it alone.


"Steve  Brusatte" <dinoland@lycos.com> wrote:

> 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 have trouble accepting that as a viable reason not to use the chevron
criteria. The closest extant relatives to dinosaurs outside the Crocodylia are
the lepidosaurs and they all have hemipenes which are a completely separate
setup. They also have completely different stances, which will effect muscle
placement. Turtles might be better creatures to look at in this matter, but
chelonian taxonomy is all over the place as it is so I'm not sure how helpful
it would be.


> 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.  


Apologies as I haven't read this, but how did Raath come to this conclusion? 

Also, how complete were these skeletons? Would it be possible to try the first
chevron criteria on them and see how it correlates with the robusticity one?

> 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.  


But crocodiles have more analogous (dare I say homologous) tails with
theropods than any other extant life form, so it is not like we're really
shooting far out there. 

Perhaps we should try it on some extinct crocs. Go from a known to an unknown
and see how it holds up.


> 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


I'd imagine it wouldn't. Birds make bad candidates for theropod penis
musculature simply because they are too derived. They dropped the use of their
tails as leg retractor bases and counterbalances. As such, the penis
musculature probably moved. One couldn't even look in extant emus and
ostriches which re-evolved their penes, since they still have no tail
connection. Mammals hardly use their tails for anything and have also
separated their penes from their rectums. Lepidosaurs have two penes to deal
with, which could throw the muscle placement off as well. 

In fact the only other animals that we could possibly compare it too would be
chelonians. AFAIK noone has done this yet.


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