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Re: Gorgosaurus



At 02:34 PM 31/01/97 -0500, Tom Holtz wrote:
>I can give you both the cladist's and the gradist's answer to the question.
>
>Cladist:  With the possible exception of a few ectopterygoid characters,
>every feature used by Russell, Carpenter, and Paul to unite Gorgosaurus and
>Albertosaurus are *primitive* characters.  However, primitive characters do
>not indicate special affinities; they are simply those features inherited by
>the common ancestor and not subsequently transformed.  (For example,
>possession of three horns does not especially unite Triceratops with
>Torosaurus, since this characteristic is shared among all ceratopsines (and,
>even more broadly, with Ceratopsidae in general)).  Since there is no
>compelling evidence that Gorgosaurus and Albertosaurus uniquely share a
>common ancestor outside of all other tyrannosaurids, and given the disfavor
>with which most cladists regard paraphyletic genera, the name "Gorgosaurus"
>for the Judith River form is to be retained.
>
What about the lacrimal "horn"?  I still don't have the Carpenter article
yet, but I though that the rectangular shaped lacrimal "horn" was something
that both libratus and sarcophagus had in common.  Tyrannosaurus does not
appear to have one and Daspletosaurus' "horn" is triangular.  Would this not
be something else to unite the two? 

>Gradist:  Albertosaurus sarcophagus is quite a distinct form from
>Gorgosaurus libratus.  Unfortunately, there are few skulls of A. sarcophagus
>on display (or even available in popular books), so the short-snouted,
>bulldoggedness of A. sarcophagus is not well appreciated.  Morphologically,
>Gorgosaurus is at least as distinct from Albertosaurus as Daspletosaurus is
>from Tyrannosaurus, so if both the latter two generic names are retained,
>both the former two should be.  (The alternative, which Greg Paul advocated
>in Predatory Dinosaurs of the World, is to sink Gorgosaurus into
>Albertosaurus AND to sink Daspletosaurus into Tyrannosaurus).
>
Ralph Molnar listed fifteen characteristics distinguishing T. rex.  When I
looked at these, some are just relative proportions, but some are a bit more
substantial.  Are the differences between libratus and sarcophagus as
substantial (or as trivial, I guess you could also say) as these?

>Note: neither of these arguements have been published yet, but are in
>preparation.
>

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...
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dinoguy@interlog.com