Re: Evolution of tyrannosauroid bite power

[don ohmes <d_ohmes@yahoo.com>]

Heh. If your arms were only 15 cm long, I would think "12 lbs" was pretty good. 
I would also think that you were still finding them useful for something, even 
if I didn't know what it was. 

The numbers you mention ain't bad for a one meter arm ... no matter what it is 
attached to.

So, the first question is, "why were the arms so little (1m)?" The second 
question is, "why were they still useful (ie, not vestigial)?" The third 
question "If they were useful, why weren't they bigger?"

Re-allocation of mass is what answers all three questions. The load had to be 
lightened somehow, and the arms were what could be spared, due to lifestyle. 
Just a cartoon, though, not currently testable (I think), other than with 
logic. Ask me what the arms were useful for, I promise a fuzzy answer neither 
critically involving, nor totally eliminating, predation. Getting up comes to 
mind ...

Don





----- Original Message ----
From: ptnorton <ptnorton@suscom-maine.net>
To: d_ohmes@yahoo.com; dinosaur@usc.edu
Sent: Sunday, December 30, 2007 4:44:06 PM
Subject: Re: Evolution of tyrannosauroid bite power


----- Original Message ----- 
From: "don ohmes" <d_ohmes@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Sunday, December 30, 2007 3:45 PM
Subject: Re: Evolution of tyrannosauroid bite power


Don Ohmes wrote, in part:

*Snip*

>that a relatively large and powerful head was absolutely essential to
 life 
>style, because it is relative >arm length that decreased (even while
 the 
>arms remained strong), rather than relative head size.

"Strong" is a relative term. Carpenter and Smith (2001) estimated the 
maximum force capable of being generated by the M. biceps in T. rex to
 be 
about 1955 N, or about 199 kg (440 pounds) per arm. Although grasping
 900 
pounds or so may sound "strong" in absolute terms, in relative terms 
(assuming a 6000-7000 kg mass for an adult T. rex) it equates to me (a
 200 
pound person) being able to curl about 12 pounds, using both arms. I
 think 
the question is not why T. rex arms were so "strong", but why were they
 so 
weak?

PTJN