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_Giganoto_ is no speedster (was RE: T rex brooding)



At 08:49 PM 8/20/98 -0700, Jamie wrote:

><The estimates I have read and/or heard is that the Giganotosaurus was
>longer & perhaps heavier than a Tyrannosaurus Rex, but not as tall or
>muscular. Does that match the Mount in Philadelphia?>
>
>  Longer, perhaps. Longer skull, definately. Taller, perhaps, but more
>muscular? Perhaps not. *Tyrannosaurus* definatelty had a stronger,
>more bulky neck, even thighs and tail, while *Giganotosaurus* was a
>slender, speedier fellow.

Speedier?  Not likely!!

_Gig._ has very robust, short, stocky legs whose proportions track
allometrically with other typical theropods (most ceratosaurs, basal
tetanurines, carnosaurs, and most coelurosaurs).

_Tyrannosaurus_ has long, slender legs whose proportions track with the
ornithomimosaurs, troodontids, caenagnathids, etc.  On top of that, they
have a certain unusual adaptation of the metatarsus, which some functional
morphometric and biomechanical work (me, 1995, JVP 14:480-519) seems to
indicate is related to enhanced cursorial ability.

Also, in _Tyrannosaurus_ (as in coelurosaurs in general), the caudofemoralis
probably terminates closer to the pelvis than in more primitive theropods,
so the anterior portion of the tail might have been "bulkier" than in
_Giganotosaurus_, but the posterior part of the tail would probably be more
slender (less muscled).

[As an aside for artists and others: PLEASE be VERY VERY cautious when
restoring proportions of the limbs and tail in _Tyrannosaurus rex_.  The
AMNH mount and those derived from it (such as the ANSP mount) have some
major errors: the legs are from a larger, more robust individual than the
rest of the skeleton, the foot is restored far to short and far to broad
(and lacking the true structure of tyrannosaurid feet), the tail of the
mount still uses _Allosaurus_ based vertebral and chevron "falsies" (when
perfectly good examples of real tyrannosaurid caudals and chevron are to be
found on the _Gorgosaurus_ models on the wall), etc.]

>A slash & run attacker, unlike the Super Rex
>(or at least, I presume not).

I seriously doubt running is much of an option for _Gig._, relative to
tyrannosaurids.  
On the matter of slashing, however, I agree most whole heartedly, as I will
discuss in a lot more detail at SVP this year (the title of my talk being
"LARGE THEROPOD COMPARATIVE CRANIAL FUNCTION: A NEW "TWIST" FOR TYRANNOSAURS").

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661