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The Lungs of Maniraptoran Dinosaurs

Proc Biol Sci. 2008 Jan 22;275(1631):157-61.
Avian-like breathing mechanics in maniraptoran
dinosaurs.Codd JR, Manning PL, Norell MA, Perry SF.
Faculty of Life Sciences, University of Manchester,
Manchester M13 9PL, UK.

In 1868 Thomas Huxley first proposed that dinosaurs
were the direct ancestors of birds and subsequent
analyses have identified a suite of 'avian'
characteristics in theropod dinosaurs. Ossified
uncinate processes are found in most species of extant
birds and also occur in extinct non-avian maniraptoran
dinosaurs. Their presence in these dinosaurs
represents another morphological character linking
them to Aves, and further supports the presence of an
avian-like air-sac respiratory system in theropod
dinosaurs, prior to the evolution of flight. Here we
report a phylogenetic analysis of the presence of
uncinate processes in Aves and non-avian maniraptoran
dinosaurs indicating that these were homologous
structures. Furthermore, recent work on Canada geese
has demonstrated that uncinate processes are integral
to the mechanics of avian ventilation, facilitating
both inspiration and expiration. In extant birds,
uncinate processes function to increase the mechanical
advantage for movements of the ribs and sternum during
respiration. Our study presents a mechanism whereby
uncinate processes, in conjunction with lateral and
ventral movements of the sternum and gastral basket,
affected avian-like breathing mechanics in extinct
non-avian maniraptoran dinosaurs.