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Re: Theropod limbs - how mobile?



----- Original Message -----
From: "Fam Jansma" <fam.jansma@worldonline.nl>
Sent: Friday, May 17, 2002 7:54 PM

> >The paper in Mesozoic Vertebrate Life explains this. *T. rex* arms are
> > incredibly strong and not vestigial in any way. [...]
>
> But...there's always a "but", how incredibly strong were the arms of T.rex
> and what was their limit of subduing or holding prey? Doubt they could
have
> held down a Anatotitan or Triceratops.

"Maximum working range" = 199 kg for the biceps alone.

Kenneth Carpenter & Matt Smith: 9. Forelimb Osteology and Biomechanics of
*Tyrannosaurus rex*, 90 -- 116 in Darren H. Tanke & Kenneth Carpenter (eds)
+ Michael W. Skrepnick (art editor): Mesozoic Vertebrate Life. New Research
Inspired by the Paleontology of Philip J. Currie, Indiana University

"Abstract

Although proportionately the forelimb is very small, the mechanical
advantage reveals an efficiently designed force-based system (vs. a
velocity-based system) used for securing its prey during predation. In
addition, the M. biceps is shown to be 3.5 times more powerful than the same
muscle in the human, the straight, columnar humerus provides maximum
strength to mass ratio to counter the exertion of the M. biceps, and the
[incredibly] thick cortical bone indicates bone selected for ultimate
strength. Such mechanical adaptations can only indicate that the arms were
not useless appendages, but were usted to hold struggling prey while the
teeth dispatched the animal. *Tyrannosaurus rex* was therefore an active
predator and not a mere scavenger, as has been suggested."

> >> When something get's progressively shorter,
> >
> >Were they getting _progressively_ shorter? Aren't all known tyrannosaurid
> >arms of pretty similar sizes?
> >
> Do I need to say more than: "Eotyrannus lengi"???

Yes. Three points are not enough to show a straight line is present. :-)

> Second, the forelimbs of
> several primitive Tyrannosaurids are not known from good material
> (Alectrosaurus, Stokesaurus) or not known at all (Alioramus) to give
precise
> comparisons to Eotyrannus. At least, from the Early Cretaceous to the Late
> Cretaceous the arms became progressively shorter within a span of about 50
> milion years (maybe longer, maybe shorter) in the Tyrannosaur group.

There's a contradiction, isn't there? -- Who mentioned PDW? *Albertosaurus
arctunguis* and *A. megagracilis* (aka *Dinotyrannus*) are now considered
young *T. rex*. While many parts of PDW do still hold, 1988 was 14 years
ago. :-)