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RE: Scaling problems in Hutchinson 2004



Kris Kripchak (MariusRomanus@aol.com) wrote:

<Has the idea of how large animals develop joints and ligament-tendon
strengths for support, instead of relying upon energy burning muscle, been
taken into account?>

  This has been dealt with in part by Holtz (1994), on defining the
arctometatarsus, and by Snively and Russell (2003) on its biomechanical
loading. Snap-ligaments and the effective control these elements have on
their adjacant bones have been taken into account for some species, and
this is also why John Hutchinson mentioned that his lab is primarily
interested in studying horses. Horses led Holtz (thesis; 1994) to
developing snap-ligaments in the arctometatarsus. Most energy-storing
ligaments I know of are helical in structure, leading to energy
conservation as, when these ligaments expand (are put under tensile
strain) they store energy as when they are contracted (are put under
compressive strain), allowing these ligaments to act as muscular "aids."
Sharks and dolphins have a "sheath" of collagen that anchors muscles that
are arranged as layers of helically wound fibers, as Wainwright et al
(1978) showed on *Negaprion,* and Lingham-Soliar (2001) showed on dolphin.
Reif and Weishampel (1986) showed that the tail sweep of a shark is
_automatic_, an effect of this energy transfer along the tendons to the
tail in the lamnid species. The L. sarcosacral is a ligament in your
pelvis that helps prevent it from dislocating from the sacrum when the
forces exerted from the leg transfer into the hip; it is helical in
structure.

  Some further references:

  http://www.elasmo-research.org/education/white_shark/skin.htm

  Reif, W. E. and D. B. Weishampel. 1986. Anatomy and mechanics of the
    lunate tail in lamnid sharks. _Zoologische Jahrbuch für Anatomie_
    114:221-234.

  Donley, J. M., C. A. Spulveda, P. Konstantinidis, S. Gemballa, and R. E.
    Shadwick. 2004. Convergent evolution in mechanical design of lamnid
    sharks and tunas. _Nature_ 429: 61-65. (w/ suppl. info.)

  Snively, E. and A. P. Russell. 2002. Kinematic model of tyrannosaurid
   (Dinosauria: Theropoda) arctometatarsus function. _Journal of
   Morphology_ 255(2):215-227.

  Some further comments:

  Hutchinson in several papers, including in Hutchinson and Gatesy, has
discussed the use of tendons in their roles in kinematic reconstruction
and the modelling of forces during movement. This is true of his 2001
papers on evolution in the hips and legs of birds, their muscular and
ligamental/tendinous analogues, and so forth.

  Snively and Russell's abstract goes further to show that ligamental
involvement has been almost the PRIMARY means by assessing function of the
anatomy:

  "We present a hypothesis of tyrannosaurid foot function termed the
   tensile keystone model, in which the triangular central metatarsal and
   elastic ligaments dynamically strengthened the foot. The tyrannosaurid
   arctometatarsus, in which the central metatarsal is proximally
   constricted, displays osteological correlates of distal intermetatarsal
   ligaments. The distal wedge-like imbrication of tyrannosaurid
   metatarsals indicates that rebounding ligaments drew the outer elements
   towards the middle digit early in the stance phase, unifying the
   arctometatarsus under high loadings. This suggests increased stability
   and resistance to dissociation and implies, but does not demonstrate,
   greater agility than in large theropods without an arctometatarsus."

  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.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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