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Uncinate processes in respiration in maniraptorans and birds

From: Ben Creisler

A new online paper:

TICKLE, P. G., NORELL, M. A. and CODD, J. R. (2012)
Ventilatory mechanics from maniraptoran theropods to extant birds.
Journal of Evolutionary Biology (advance online publication)
doi: 10.1111/j.1420-9101.2012.02465.x

Shared behavioural, morphological and physiological characteristics
are indicative of the evolution of extant birds from nonavian
maniraptoran dinosaurs. One such shared character is the presence of
uncinate processes and respiratory structures in extant birds. Recent
research has suggested a respiratory role for these processes found in
oviraptorid and dromaeosaurid dinosaurs. By measuring the geometry of
fossil rib cage morphology, we demonstrate that the mechanical
advantage, conferred by uncinate processes, for movements of the ribs
in the oviraptorid theropod dinosaur, Citipati osmolskae, basal
avialan species Zhongjianornis yangi, Confuciusornis sanctus and the
more derived ornithurine Yixianornis grabaui, is of the same magnitude
as found in extant birds. These skeletal characteristics provide
further evidence of a flow-through respiratory system in nonavian
theropod dinosaurs and basal avialans, and indicate that uncinate
processes are a key adaptation facilitating the ventilation of a lung
air sac system that diverged earlier than extant birds.