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Re: Baby birds to feathered dinosaurs: incipient wings and evolution of flight



From: Ben Creisler
bcreisler@gmail.com

Apparently my first attempt to send this posting today was lost in
cyberspace like a number of other recent items I have tried to send to
the DML. I'll see if sending a reply works....

On Thu, May 8, 2014 at 11:02 PM, Ben Creisler <bcreisler@gmail.com> wrote:
> From: Ben Creisler
> bcreisler@gmail.com
>
>
> A new online paper:
>
>
> Ashley M. Heers , Kenneth P. Dial , and Bret W. Tobalske (2014)
> From baby birds to feathered dinosaurs: incipient wings and the
> evolution of flight.
> Paleobiology 40(3): 459-476
> doi: http://dx.doi.org/10.1666/13057
> http://www.bioone.org/doi/abs/10.1666/13057
>
> Reconstructing the tree of life requires deciphering major
> evolutionary transformations and the functional capacities of fossils
> with “transitional” morphologies. Some of the most iconic,
> well-studied fossils with transitional features are theropod
> dinosaurs, whose skeletons and feathered forelimbs record the origin
> and evolution of bird flight. However, in spite of over a century of
> discussion, the functions of forelimb feathers during the evolution of
> flight remain enigmatic. Both aerodynamic and non-aerodynamic roles
> have been proposed, but few of the form-function relationships assumed
> by these scenarios have been tested. Here, we use the developing wings
> of a typical extant ground bird (Chukar Partridge) as possible
> analogues/homologues of historical wing forms to provide the first
> empirical evaluation of aerodynamic potential in flapping theropod
> “protowings.” Immature ground birds with underdeveloped, rudimentary
> wings generate useful aerodynamic forces for a variety of locomotor
> tasks. Feather development in these birds resembles feather evolution
> in theropod dinosaurs, and reveals a predictable relationship between
> wing morphology and aerodynamic performance that can be used to infer
> performance in extinct theropods. By spinning an ontogenetic series of
> spread-wing preparations on a rotating propeller apparatus across a
> range of flow conditions and measuring aerodynamic force, we explored
> how changes in wing size, feather structure, and angular velocity
> might have affected aerodynamic performance in dinosaurs choosing to
> flap their incipient wings. At slow angular velocities, wings produced
> aerodynamic forces similar in magnitude to those produced by immature
> birds during behaviors like wing-assisted incline running. At fast
> angular velocities, wings produced forces sufficient to support body
> weight during flight. These findings provide a quantitative,
> biologically relevant bracket for theropod performance and suggest
> that protowings could have provided useful aerodynamic function early
> in maniraptoran history, with improvements in aerodynamic performance
> attending the evolution of larger wings, more effective feather
> morphologies, and faster angular velocities.