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Re: What is biomechanics? (or, The Truth About Flying Snakes - Was: Re: science and philosophy)



Colin McHenry (cmchenry@westserv.net.au) wrote:

[...]

  Though I appreciate greatly Colin's approach to this thread, I got the
odd feeling my words were taken from a purely anatomical and mechanical
perspective and relayed into an evolutioary one. I emplyed Occam's Razor
not as a cladistic support but simply as a method to gague form in
function. Phylogeny had little to do with what I had written. I may
perform cladistic excercises, but i am no cladist; a scientist can be a
scientist despite the methodology and practice. For example, we can diss
Drs. Feduccia and Ruben for [some of] their methods, but they are in their
fields quite accomplished scientists and I agree with Alan on many things
strictly avian, and John on some things strictly crocodilian and
metabolic.

  Anyway, since the thesis of my post was on the nature of biomechanics, I
will focus on Colin's critique of my post on that score.

  A forelimb's operation is succinct, and bound by the joints; in the
shoulder joint of birds, as I would like to elucidate for Tracy's sake
especially, is very mobile. It bears virtually no limitations or
constraints. Not so that of most theropod dinosaurs. Resultant to this,
birds have a great deal of shoulder mobility, but as the critics to the
Stevens/Parrish work on sauropod neck joints have said, it takes more than
bones to make a neck move, extend it, or constrain it. Muscles, sinovia,
menisci, and cartilage constrains the limbs of vertebrates, and this can
be seen in experimenting with a crocodile limb, where the shoulder is very
mobile. This is due to the nature of a laterally facing glenoid socket and
no shalving ridges to constrait the humerus ... on top of that, the
humeral caput is condylar and subcircular in section, providing great ease
of position. The effects of muscles on the shoulder and humerus, which I
was describing earlier, are the biomechanical "unstable trusses" that must
be employed and analyzed. The shoulder of *Velociraptor* is no different,
and comparison would serve us well. The effective movements I described by
Novas and Puerta on *Unenlagia* and by Erickson on *Torosaurus* are the
same and are, contra Colin, biomechanical in nature. I can describe the
functional morphology of the scapular glenoid, but the relation between a
humerus and shoulder girdle are biomechanical.

  To test the mechanics of arm-shoulder relation, Per Erickson and his
team constructed a forelimb of a recently recovered *Torosaurus*, added
elastic bands to simulate the positions and arrangement of the major
flexors/adductors, extensors/abductors, and applied mechanical movements
to it, in order to assess the flexibility and constraints of the arm.
Today, Stevens' DinoMorph program has the potential to do this when bones
are digitally scanned, using the research that the Triceratops Project
(tm), headed by former list member Ralph Chapman. 

  This can be done for a bird's shoulder, for complete recovered
*Deinonychus* shouders, for models of *Archaeopteryx*, etc, in order to
determine constraits and permissions in the biomechanism. I see no flaw in
this method, and it was this that I alluded to previously. One does not
need a cladistic program to perform any part of this excercise.
Furthermore, I alluded to the EPB of Witmer, and in this the application
was to relations of muscles, sites for muscles, and types of muscles. This
can permit a better understanding of ranges of constraints during muscular
effect. Carranno and Hutchinson, 2002, have provided that sites for
muscles can help determine size for muscles, as seen in Hutchinson and
Garcia, 2002, for which effect of muscle power can be determined.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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