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

On Sunday, May 19, 2002, at 05:13 AM, David Marjanovic wrote:

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.

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.

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).

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.

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

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.

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.

This is what I am picturing. I'll draw a picture.

John Conway, Palaeoartist

"All art is quite useless." - Oscar Wilde

Protosite: http://homepage.mac.com/john_conway/
Systematic ramblings: http://homepage.mac.com/john_conway/phylogenetic/