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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
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-----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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