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RE: Discovery tonight ... 8 pm



One thing that I absolutely _must_ make clear is that I do not, in any way, 
shape, or form, agree with how that senquence on the show depicted the proposed 
kinesis working. The way that they protrayed the lower jaw literally becoming 
"unhinged" from the quadrate was totally wrong, no arguments here.

~ Michael

> CC: dinosaur@usc.edu
> From: habib@jhmi.edu
> To: tehdinomahn@live.com
> Subject: Re: Discovery tonight ... 8 pm
> Date: Mon, 7 Dec 2009 15:33:20 -0500
>
> On Dec 7, 2009, at 2:17 PM, Michael Erickson wrote:
>
>> I don't know what this tyrannosaur cranial kinesis hating is really
>> all about, maybe that one Witmer paper? But I still beleive that it
>> occurred. Apparrently so does Pete Larson. One single little paper
>> (yes, I've read it top to bottom, and I do find it rather poor, but
>> that's another story) isn't going to convince me that all of the
>> previous work done by too many workers to count since the early
>> 1900s is completely wrong. Now you can attack me for this. And then
>> attack me for expecting to be attacked. (For the record, I'm only
>> half-joking.)
>
> Part of the concern with that particular sequence in the show is that
> the kinesis that was shown involves a full disarticulation of the jaw
> joint. There are a number of issues with this, and it seems to have
> its origins (as a common speculation) in the rampant misconception
> that snakes do something like that. In reality, the only squamate
> joint that "disarticulates" (though not really) is the contact between
> the two mandibles - they don't have a fused symphasis, and the
> ligament there is elastic, so the bones do spread apart. The
> articulation of the lower jaw with the skull proper *looks* like it
> separates in snakes, but that's actually a widely swinging quadrate,
> that effectively produces a two-joint system for depression of the
> lower jaw. The bones do not lose contact.
>
> This is a common theme: in animals with kinetic skulls (scleroglossans
> - snakes included, birds, teleost fish, etc) the motion occurs
> primarily because joints are mobile and/or numerous - not so much
> because the joints come apart. Snakes have hyper-kinetic skulls
> because they have a whole lotta joints in there. If we are to suppose
> a kinetic skull for tyrannosaurids, we need to find some joints.
>
> So, in short, if we are to suppose kinesis in the tyrannosaurid skull,
> we have to ask: where does it happen? There is an intramandibular
> joint in some theropods that can add kinetic aspects, but it is
> apparently not very mobile in tyrannosaurids. Same goes for skull
> roof, palatal elements, etc. In really kinetic skulls, the elements
> essentially hang from the braincase - but tyrannosaurs are basically
> the opposite. That leaves a lot of skepticism regarding the ability
> of the tyrannosaur skull to undergo kinetic deformations, because
> there just aren't any joints for it to happen at.
>
> Cheers,
>
> --Mike H.
>
>
> Michael Habib
> Assistant Professor of Biology
> Chatham University
> Woodland Road, Pittsburgh PA 15232
> Buhl Hall, Room 226A
> mhabib@chatham.edu
> (443) 280-0181
>                                         
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