Laminarity in Avian Long Bones

["Jaime A. Headden" <qilongia@yahoo.com>]

A paper from last year has not yet been mentioned on the list, and has
some bearing on the biomechanics of avian flight, so I thought I'd mention
it.

  de Margerie, E. 2002. Laminar bone as an adaptation to torsional loads
in flapping flight. _Journal of Anatomy_ 201: 521-526.

  Abstract -- Using a new histometric method, the orientation of primary
osteons was measured in the main long bones of adult mallards (*Anas
platyrhynchos*). In the light of previous biomechanical and ontogenetic
studied, a functional hypothesis is proposed, explaining the histological
differences observed between long bones; laminar bone tissue, mainly found
in the wing bones, may be a biomechanical adaptation to torsional loads
caused by flapping flight.

  Suggests the presence of particular orientations of primary osteons may
indicate the increased usage of the wings in flapping, and may best permit
an analysis of which animals were flapping for adding greater loading onto
their wings, versus those that weren't, and perhaps differentiate flappers
from gliders. Subsequent histological studies include de Ricqlés et al.
(2003, _JVP_ 23(2): 373-386) in which the sections for the limbs may
compare. De Margerie limited her study to the mallard, but opens the floor
for more avian taxa to be added, using her given criteria for assessing
laminarity in bones:

  laminarity = the value of the circular vascular orientation, divided by
the summed values for the circular, oblique, radial, and longidtunidal
vascular orientations.

  In this,  the highest degree of laminarity was found in the forelimb
versus the hind, and the highest degree of laminarity of the forelimb in
the ulna, whereas the radius had a value simialr to the tibia, but
slightly higherl meanwhile, the femur has a value greater than the radius,
similar to the humerus, but not as much as in the carpometacarpus. The
reasons for these are not fully understood, and de Margerie calls them
"anomolous" cases, but approaches them thusly: the radius appears to
exhibit little torsion, and its known function is to facilitate wing
folding as a "pushrod," the the loading on the wing transmit into the
ulna, rather than the radius. The femur exhibits high torsion because it
is horizontal, the effect of walking causing it to twist (Carrano, 1998;
Carrano & Biewener, 1999). The radius, like the rest of the hindlimb,
undergo more tension/compression then do the forelimb/femur, so this
divergence of expression of laminarity is expected.

  Citations:

  Carrano, M.T. 1998. Locomotion in non-avian dinosaurs: Integrating data
    from hindlimb kinematics, _in vivo_ strains, and bone morphoplogy.
    _Paleobiology_ 24: 450-469.

  _____________ & Biewener, A.A. 1999. Experimental alteration of limb
    posture in the chicken (*Gallus gallus*) and its bearing on the use of
    birds as analogs for dinosaur locomotion. _Journal of Morphology_ 240:
    237-249.

  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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