RE: T. rex forelimbs (was Carnotaurus)

["Tracy Ford" <dino.hunter@home.com>]

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Thomas R. Holtz, Jr.
Sent: Tuesday, April 24, 2001 5:50 AM
To: rbi@dana.ucc.nau.edu; dinosaur@usc.edu
Subject: RE: T. rex forelimbs (was Carnotaurus)

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> R. Irmis
>
> <<It could be possible that the more robust arms are an
> allometric result of
> increased body size, not because they had a specific "use".>>
>
> This wouldn't be considered robust then.  If the arms simply increase
> proportionally with size, they would still be as gracile as before.
> Evidently, the size of the bones and proportions are larger than if one
> simply scaled up an *Albertasaurus* to *Tyrannosaurus* size.

Being somewhat familiar with the tyrannosaur literature (;-), I can say that
NO ONE has yet published a study plotting relative robusticity of tyrant
dino arms with increasing size.  As such, it has yet to be demonstrated that
_Tyrannosaurus rex_ has considerably more powerfully built arms than a
_Gorgosaurus_ or _Albertosaurus_ scaled up to that size.  (_Tarbosaurus
bataar_, though, does seem to have greater reduction of the forelimb than
_T. rex_).

However, comparing equivalent sized humeri of _Tyrannosaurus rex_ and
_Acrocanthosaurus_ (a similar sized taxon), we see that they are of
comparable length, but the latter has MUCH larger muscle attachments.
Tyrannosaurid limbs, in general, were lightly muscled compared to   the arms
of at least that big carnosaur.

The femur/humerus ratio for T.rex is 1:3,

In Tarbosaurus, Albertosaurus, Gorgosaurus it is 1:4,

This would mean that the arms in Tyrannosaurids was getting bigger in the
Maastrichtian not smaller.

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074