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Re: Vestigial Arms (was: Theropod limbs - how mobile?)

----- Original Message -----
From: "John Conway" <john_conway@mac.com>
Sent: Saturday, May 18, 2002 8:35 PM

> Excuse my further skepticism, but we don't really know how big the
> muscles were, do we? How can we really know how strong they were?

Oh, sorry. Forgot to write that: Muscle attachment sites. How big are they,
and where exactly are they? What diameters would the tendons therefore have,
and at what angles would they be positioned? What would various mechanical
advantages be? That sort of thing. All quantifiable.

> To get an effective grip with its arms a tyrannosaurid would have at
> least its chest in contact with its prey, and almost certainly one thigh
> as well. Enough to severely restrict movement.

Which was the purpose -- the prey shouldn't move, and only the predator's
head and neck should move :-)

> Try this: tie yourself to someone else (close like a T. rex) and get
> them to thrash about like they're being bitten. I bet you both fall
> over, because you cannot shift your balance or move your legs properly.
> Now, if you both weigh several tonnes, this is going to hurt, and you
> may break your legs.

Hm. My center of gravity is maybe half a meter above my hip joints instead
of between them, and I don't have a tail. And *T. rex* can stop anyone
thrashing about :-)

> It would explain the pulling muscles if they stood side by side, and
> hooked hands, trying to pull each others arms outward.

Very difficult according to Fig. 9.13C. The claws point inwards, and any
rotation of the forearm is impossible.