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Flapping-based locomotory hypotheses in bird antecedents (free pdf)

Ben Creisler

A recent paper as open-access PeerJ preprint:

T. Alexander Dececchi, Hans C.E. Larsson & Michael B. Habib (2016)
The wings before the bird: an evaluation of flapping-based locomotory
hypotheses in bird antecedents.
PeerJ PrePrints 4:e1676v1
doi: https://doi.org/10.7287/peerj.preprints.1676v1

Background. Powered flight is implicated as a major driver for the
success of birds. Here we examine the effectiveness of three
hypothesized pathways for the evolution of the flight stroke, the
forelimb motion that powers aerial locomotion, in a terrestrial
setting across a range of stem and basal avians: flap running, Wing
Assisted Incline Running (WAIR), and wing-assisted leaping. Methods.
Using biomechanical mathematical models based on known aerodynamic
principals and in vivo experiments and ground trothed using extant
avians we seek to test if an incipient flight stroke may have
contributed sufficient force to permit flap running, WAIR, or leaping
takeoff along the phylogenetic lineage from Coelurosauria to birds.
Results. None of these behaviours were found to meet the biomechancial
threshold requirements before Paraves. Neither was there a continuous
trend of refinement for any of these biomechanical performances across
phylogeny nor a signal of universal applicability near the origin of
birds. None of these flap-based locomotory models appear to have been
a major influence on pre-flight character acquisition such as
pennaceous feathers, suggesting non-locomotory behaviours, and less
stringent locomotory behaviours such as balancing and braking, played
a role in the evolution of the maniraptoran wing and nascent flight
stroke. We find no support for widespread prevalence of WAIR in
non-avian theropods, but can’t reject its presence in large winged,
small-bodied taxa like Microraptor and Archaeopteryx. Discussion.
Using our first principles approach we find that “near flight”
locomotor behaviors are most sensitive to wing area, and that
non-locomotory related selection regimes likely expanded wing area
well before WAIR and other such behaviors were possible in derived
avians. These results suggest that investigations of the drivers for
wing expansion and feather elongation in theropods need not be
intrinsically linked to locomotory adaptations, and this separation is
critical for our understanding of the origin of powered flight and
avian evolution.