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proportional differences (was bulldog tyrranosaurs)



At 10:52 AM 05/02/97 -0700, Jeff Martz wrote:
>    I can't speak for species or genus distinction, but if you are
>referring to sexual dimorphism, the "robust" and "gracile" morphs seen is
>Coelophysis, Syntarsus, and apparantly Tyrannosaurus as well, are not
>totally random variations in size or morphology across the population.
>There are two distinct size classes, and particular suites of
>morphological characteristics which characterize the size classes.  The
>dimorphism in T.rex is still fairly controversial (being a smaller smale
>size), but there is less doubt about it in the Ghost Ranch theropods. 
>Check out the papers on these three theropod genera in "Dinosaur
>Systematics". 

I have seen the evidence for male/female Coelophysis and Syntarsus
specimens.  The robust/gracile argument works in that case (probably), but
that was not the gist of my point.  I was more refering to animals of
different sizes being called different species or genera.  I know it can be
difficult (George Olshevsky's leopard/lion arguement), I want to know where
we start to draw the line.

As to Tyrannosaurus, I am not so sure the gracile/robust arguement works as
well.  Last count I saw had 2 robust and 13 gracile.  Could it be that one
group is just randomly bigger?  From higher in the formation? Older?
Diseased?  Etc.?

>      Has anyone confirmed Pete Larson's claim about the size and
>placement of the first caudal chevron?  Has anyone even bothered to look
>for this feature in other theropods?

Last I heard (Horner and Lessem's T. rex book in 1993), that part of the
tail was jumbled in "Sue".  I also would find it odd that there seem to have
been more males than females, but that could be poor sampling.
Darryl

----------------------------------------------------------
"the truth is, I don't really care how the dinosaurs died.
I'm interested in how they lived."  (Dr. John R. Horner,
from the Complete T.rex, 1993)
Although the Mike Harris cutback theory intrigues me...
---------------------------------------------------------- 
dinoguy@interlog.com