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Re: Do not misunderestimate the king was Re: Evolution of tyrannosauroid



"[ ... ] it is impossible, because *T. rex*, too, was incapable of 
pronating its forearms. Put the edges of your hands on the table; this
 is 
the position *T. rex* was capable of. You'll see that digging the claws
 into 
the ground was not an option. (Plus, its wrists were almost immobile.)
 Also, 
how should this produce an avulsion of the tendon of the M. triceps,
 which 
is a forearm extensor?" -- DM.

Assuming that any T.rex or functional equivalent that ended up on it's back 
after a fall would need to roll over onto it's stomach in the process of 
getting up, then levering the body center of mass toward the feet w/ the snout 
prior to standing up and/or moving the feet forward (under the cm) would seem 
necessary. Logically, the arms might be useful in providing roll-wise 
stability, or even minimal thrust in such maneuvers, although ill-suited for 
such, even as you say. 

However, if data support the existence of an arm-strength hierarchy in the 
large-jawed mega-bipeds, w/ T. rex at the top, then such arm-strength 
differentials would argue _against_ including any 'getting up' scenarios in a 
selective regime governing arm strength. Assuming all the largest species were 
equally subject to falling, and that a fall was not a death sentence, as seems 
reasonable.

Don

----- Original Message ----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Tuesday, January 1, 2008 8:31:19 PM
Subject: Re: Do not misunderestimate the king was Re: Evolution of 
tyrannosauroid

----- Original Message ----- 
From: "Dann Pigdon" <dannj@alphalink.com.au>
Sent: Wednesday, January 02, 2008 1:51 AM

> I'm skeptical that *adult* tyrannosaur forelimbs were used to capture
 or
> manipulate prey at all. It wouldn't matter how strong the arm muscles
> themselves were if the shoulder joints weren't up to withstanding the
 
> forces
> generated by struggling multi-tonne prey.

What is not stable about the shoulder joints? And doesn't the tendon 
avulsion illustrated by Carpenter & Smith (2001) look rather fresh?

> If I were an adult tyrannosaur,
> I'd rather use my massive jaw and neck muscles to subdue prey - or
 use a
> 'bite and retreat' method and not attempt to hold onto prey at all.

The latter is what all other theropods of this size seem to have used.
 They 
had weak jaw muscles and normal archosauriform teeth (recurved,
 compressed 
from side to side). Unlike tyrannosaurs. The other method could benefit
 from 
arms holding the prey between two bites if the first bite (that catches
 the 
prey) doesn't suffice to stop it from fighting or running away.

> Perhaps the main use adult tyrannosaurs had for their forelimbs was
 to 
> help them rise from a crouching position? [...]

You are describing exactly Newman's (1970) scenario. As I explained 
yesterday, it is impossible, because *T. rex*, too, was incapable of 
pronating its forearms. Put the edges of your hands on the table; this
 is 
the position *T. rex* was capable of. You'll see that digging the claws
 into 
the ground was not an option. (Plus, its wrists were almost immobile.)
 Also, 
how should this produce an avulsion of the tendon of the M. triceps,
 which 
is a forearm extensor?

On the problem of how the poor beast did stand up, it has long been 
suggested that it was no problem to extend the legs in such a way that
 the 
animal stood up vertically. Ratites do it that way, and while *T. rex*
 had a 
much heavier head and neck, it also had a fairly reasonable tail...