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



----- Original Message -----
From: "John Conway" <john_conway@mac.com>
Sent: Sunday, May 19, 2002 6:40 AM

> This can be put in simpler terms. Ceratopsid of hadrosaurid legs
> powering escape, vs tyrannosaur arms preventing it. Compare the bone
> strengths and muscle masses: legs win, by a long, long way.

And will drive the claws even deeper into the flesh. Not to mention that the
tyrannosaur has already bitten.

> > Which was the purpose -- the prey shouldn't move, and only the
> > predator's
> > head and neck should move :-)
>
> Movement is necessary for the predator to maintain balance. They prey is
> NOT going to stop moving its legs because tyrannosaurid arms are lodged
> in its back (well not right away anyhow).

Not its back. Its sides. I have a poster of a great painting by Brian
Franczak (1991) hanging on a door; it shows 3 *T. rex* chasing a herd of
*Edmontosaurus regalis*. One *T. rex* is biting an *E. regalis* into the
tail from above (similar to the famous neural spine bitten off a
*Saurolophus* tail by a *T. rex*), while its hands reach the ventrolateral
parts of the tail.

> > 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 :-)
>
> Well, tie a couple of big dogs together, same result, I think.  Legs get
> tangled when they cannot move through their full arc.

Too many legs in your example :-)

> If a tyrannosaurid's prey lurched toward it, then one leg would go
> underneath the herbivore,

No, why?

> and it would not be able to swing its tail far
> enough to correct its balance, because the preys body or tail would be
> in the way.

When the tyrannosaur attacks from behind, that is. Maybe it avoided that.

> What's the point of such risky hunting techniques anyway? The bite size
> GSP calculated in PDW looks big enough to fell a Triceratops without
> repeated biting or grappling.

To do this with the *E. regalis* in the painting, it would have to bend its
neck very far to a side... the head would have to be level with the
shoulders.

> > Very difficult according to Fig. 9.13C. The claws point inwards, and any
> > rotation of the forearm is impossible.
>
> This is what I am picturing. I'll draw a picture.

I look forward to that :-)