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Uncinate paper + dissertation
Peter G. Tickle, A. Roland Ennos, Laura E. Lennox, Steven F. Perry, and
Jonathan R. Codd (2007). Functional significance of the uncinate processes in
birds. Journal of Experimental Biology 210: 3955-3961.
Summary: "The functional significance of the uncinate processes to the
ventilatory mechanics of birds was examined by combining analytical modeling
with morphological techniques. A geometric model was derived to determine the
function of the uncinate processes and relate their action to morphological
differences associated with locomotor specializations. The model demonstrates
that uncinates act as levers, which improve the mechanical advantage for the
forward rotation of the dorsal ribs and therefore lowering of the sternum
during respiration. The length of these processes is functionally important;
longer uncinate processes increasing the mechanical advantage of the Mm.
appendicocostales muscle during inspiration. Morphological studies of four bird
species showed that the uncinate process increased the mechanical advantage by
factors of 2–4. Using canonical variate analysis and analysis of variance we
then examined the variation in skeletal parameters in birds with different
primary modes of locomotion (non-specialists, walking and diving). Birds
clustered together in distinct groups, indicating that uncinate length is more
similar in birds that have the same functional constraint, i.e. specialization
to a locomotor mode. Uncinate processes are short in walking birds, long in
diving species and of intermediate length in non-specialist birds. These
results demonstrate that differences in the breathing mechanics of birds may be
linked to the morphological adaptations of the ribs and rib cage associated
with different modes of locomotion."
For further reading on the functional morphology of uncinate processes (in a
more maniraptoran/dinosaurian context), you can also check out...
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