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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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