Summary: Allen et al. (2013)

Neornithes (living birds) locomote by feather-aided flight and they have a bipdeal crouched hindlimb support structure that facilitates walking / running. The evolution of both these traits is controversial, however, computer modelling and well preserved specimens are paving the way for identifying the underlying biomechanics of locomotion. Allen et al. (2013) digitally reconstructed the body morphology of species across the Archosauria clade (17 species), using three-dimensional reconstruction of body shape, to measure the trends in evolutionary locomotor biomechanics. Species used included the four major species representing major key stages in avian body plan evolution: Microraptor, Archaeopteryx, Pengornis and Yixianornis. Allen et al. (2013) suggest that a more-crouched limb posture was acquired gradually in a step-wise fashion through theropod evolution, although this was accelerated in the Maniraptoran clade. They also found that enlargement of the pectoral limb, with other associated trends, had a stronger influence on the evolution of hindlimb posture than tail reduction. Within the Manirapotra, Allen et al. (2013) also found that the evolution of flight is closely correlated with the accelerated morpho-functional trends observed. They suggest that anatomical novelties in the pelvic and pectoral limbs is closely linked to the evolution of flight in birds.