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


On Sunday, May 19, 2002, at 04:02 AM, David Marjanovic wrote:

"Maximum working range" = 199 kg for the biceps alone.
Not estimates, calculations :-) The math is spread over several pages, so I
won't explain it here (hm... sounds as if I'd understand it :-> ) 

I wouldn't understand anyway. I'm an artist, not exactly a math whizz.

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?

I don't understand how we can be certain about the arms, and yet the legs................ you know where I'm going with that.

To get their
hand claws lodged in their prey would require tyrannosaurids to get very
close, with wide areas of contact with their prey.

Were they so broad?

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.

At such close
quarters, a simple shift in weight from the herbivore would throw the
tyrannosaurid off balance, because its movement would be severely
restricted.

Should depend on the tyrannosaur's leg muscles...

Not really, because its movement was restricted by the animal it was holding on to.

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.

It has been suggested before (sorry, I can't remember who it was) that
they used their arms for intraspecific contests. The arms were small to
keep them out of the way, and save energy growing them, yet they
remained muscular for arm-wrestling with rivals.

Wouldn't explain the strong pulling muscles, I think, and the fingers:
"Finally, to ensure that the struggling prey not escape while the mouth is
attempting to kill it, the two ungual claws [sic] point somewhat inward
(fig. 9.13C) so that they do not slip out of the prey easily.

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

Maybe this description is enough:
"We envision that *T. rex* stalked or ambushed prey, mostly subadult
or young adult hadrosaurs (see Carpenter 2000). As with most extant
predators, the mouth was used to grasp the prey. Then the short, powerful
arms were used to grasp or clutch the prey against the body to prevent its
escape while the teeth were disengaged and repeated bites made to kill the
prey."
:-)

Nope, didn't do it for me, just can't picture it. (And that's my job!) :-)


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/