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Re: Evolution of tyrannosauroid bite power



"Tyrannosaur forelimbs were clearly 
undergoing strong selection of some sort across phylogenetic space as 
they shrank, reduced digits, and otherwise altered the heck out of the 
morphology; if they were undergoing selection for prey manipulation I 
would expect the safety margin to be higher." -- Scott Hartman

Yes. Also, it is unexpected that extreme shortness of the forearms would 
represent the optimal prey manipulation tool shape within bipeds. Further, the 
existence of other very large carnivorous bipeds with extremely dinky arms that 
are NOT unexpectedly strong (ie, as strong as those of T rex) would argue 
strongly against the idea that arm shortness is result of selection for 
predatory behavior. Instead, arm shortness is logically the end result of other 
common factors; very large body size, combined with the need for very large 
jaws (and related equipment), and an active bipedal lifestyle. Mass 
re-allocation, in a word. Er, two words.

Don

----- Original Message ----
From: "dinoboygraphics@aol.com" <dinoboygraphics@aol.com>
To: Ken.Carpenter@dmns.org; ptnorton@suscom-maine.net; d_ohmes@yahoo.com; 
dinosaur@usc.edu
Sent: Wednesday, January 2, 2008 11:44:42 AM
Subject: Re: Evolution of tyrannosauroid bite power

>>It seems pointless to continue this discussion since you admit that 
you
>>cannot see how a strongly built arm with a high incidence of 
pathologies
>>indicating struggling prey do not logically indicate an active 
predator.

Maybe I should have read this series of posts more carefully, but there
 
seem to be 2 separate arguements here:

1) What can be inferred about general T. rex  behavioral ecology from 
the incidence of pathologies in the forelimbs

2) What can be said about the function of the forelimbs themselves

Regardless of how the forelimbs were used, it isn't unreasonable to say
 
that a high incidence of pathology indicates frequent (and violent) 
activity.  Being a carnivore, predatory behavior is an obvious 
potential source of the pathologies.  Hypothetically, they could be 
 from interspecific activity or locomotory mishaps (walking into trees,
 
or falling down).  In the former case I'd expect a bimodal distribution
 
(along genderal lines) and in the latter case I'd expect the forelimbs 
to be shattered beyond the damage seen, so I don't think Ken is too far
 
out on a limb here (sorry, pun sadly intended...) to say that a high 
degree of forelimb injuries is more consistent with an actively 
predatory T. rex than it is with a purely scavenging behavioral model.

That said, we are still left with the "What the heck did the arms do?" 
issue.  Ken (Carpenter & Smith, 2001) suggest that the arms may have 
been used to help subdue struggling prey; in this case I think Mike 
Habib's observation about selection and pathologies is pertinent.  It's
 
certainly true that animals are not optimized the way an engineer 
would, but it's also true that organisms usually maintain a relatively 
high safety margin when there are strong selective pressures relating 
to behavior and mechanical stress.  Tyrannosaur forelimbs were clearly 
undergoing strong selection of some sort across phylogenetic space as 
they shrank, reduced digits, and otherwise altered the heck out of the 
morphology; if they were undergoing selection for prey manipulation I 
would expect the safety margin to be higher.

I would take the high level of pathologies to indicate that an active 
predator was getting them banged up, but probably not (intentionally) 
using them in the hunt.  Of course what a predator "intends" to do and 
what ends up happening are often two different things, and it's 
unreasonable to say that the forelimbs (and anything else available) 
weren't used if a rogue edmontosaur or ceratopsian started to turn the 
tables on a luckless predator, but I don't see compelling evidence that
 
the forelimbs were specialized for prey aquisition.

As for other behaviors (display, carcass lifting, transport of meat to 
young, etc) those are all possible, and as near as I can determine 
untestable at the moment (and I think all involved have agreed).


Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message-----
From: Ken.Carpenter@dmns.org
To: ptnorton@suscom-maine.net; d_ohmes@yahoo.com; dinosaur@usc.edu
Sent: Tue, 1 Jan 2008 2:03 pm
Subject: RE: Evolution of tyrannosauroid bite power



It seems pointless to continue this discussion since you admit that you
cannot see how a strongly built arm with a high incidence of
 pathologies
indicating struggling prey do not logically indicate an active
 predator.
You may believe as you wish about carcass lifting.

Kenneth Carpenter, Ph.D.
Curator of Lower Vertebrate Paleontology & Chief Preparator
Department of Earth Sciences
Denver Museum of Nature & Science
2001 Colorado Blvd.
Denver, CO 80205 USA

Office phone: 303-370-6392
Museum fax: 303-331-6492
---------------------------------------------------------------
For PDFs of some of my publications, as well as information of the
 Cedar
Mountain Project:
https://scientists.dmns.org/sites/kencarpenter/default.aspx
(if you have problems with the link, cut and paste it into the browser
address bar)
-----------------------------------------------------------------
The scientific method is a myth:
http://www.dharma-haven.org/science/myth-of-scientific-method.htm
--------------------------------------------


-----Original Message-----
From: ptnorton [mailto:ptnorton@suscom-maine.net]
Sent: Tuesday, January 01, 2008 1:58 PM
To: Ken Carpenter; d_ohmes@yahoo.com; dinosaur@usc.edu
Subject: Re: Evolution of tyrannosauroid bite power

>Unfortunately, your carcass-pumping hypothesis can not be verified.<

It's carcass lifting, not carcass pumping. And, as I said, I agree that
the
behavior of extinct animals can't be tested directly.

>Smith and I at least constrained our interpretation to  what can be
verified by others.<

I have no argument with the biomechanical work in Carpenter and Smith
(2001). But the conclusion about predatory behavior does not logically
follow from that work.

>We might as well say that T rex used its arms to
build an advanced civilization and the lack of artifacts is simply
because we haven't yet found them, not that they don't exist. <

You can say that if you wish, but I certainly don't.

PTJN




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