Frog Urostyles on the Dino List???

["Matthew Bonnan" <mbonnan@hotmail.com>]

> At 12:40 PM 07/07/2000 -0700, Jaime A. Headden wrote:
> > And
> > the reason for this little tidbit is a question:
> > What's the anuran urostyle for?

And Ronald Orenstein responded:

> Perhaps for the attachment of tail-wagging muscles in tadpoles?  Ascaphids
> and Leiopelmatids (I think) retain vestiges of such muscles in adulthood.

Hot diggity!  Functional questions are coming out of the woodwork.  And here 
I thought we'd never end the systematics debate! =)  There is an excellent 
paper on just this question:

Jenkins, F. A. and Shubin, N. 1998. _Prosalirus bitis_ and the anuran 
caudopelvic mechanism. Journal of Vertebrate Paleontology, 18(3): 495-510.

The basic functional gist of the article is that the urostyle, sacrum, and 
ilium work together as a kind of spring that assists frogs in doing what 
they do best: jumpin'.  From the abstract:

"Mobile sacro-urostylic and ilio-sacral joints are important kinetic links 
in the anuran caudopelvic mechanism for saltation.  The angular appearance 
of the back common among living anurans reflects a pronounced flexure at the 
sacro-urostylic and ilio-sacral joints.  During the launch phase of a jump, 
the sacrum+presacral vertebral column extends at these joints by the action 
of the longissimus dorsi muscles, aided by forelimb thrust.  The urostyle 
remains fixed between the ilia by the coccygeo-iliacus muscles that transmit 
propulsive thrust from the ilia to the urostyle, and thence to the sacrum 
and presacral column."

Locomotion: how can you not love it? =)  Find me a urostyle in a sauropod, 
and I'll show you a REAL thunder lizard. =) =P  Hey, I figure if you can 
claim that sauropods reared tripodally and were supported by those really 
strong legs, they must have been able to jump even better than elephants!

Matt Bonnan

"Here where you are standing / The dinosaurs did a dance ..."
-- Talking Heads, "City of Dreams"
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