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Re: vaulting pterosaur launch, questions



Sorry to switch focus from pterosaurs to birds, but how do you
picture
_Archaeopteryx_ getting itself airborne from terra firma? By leaping from a
standstill off the ground? <<<


That presumes, of course, that Archaeopteryx got airborne for any significant period of time at all. It continues to amaze me how we can have discussions using Archaeopteryx as the pivot point for "origin of flight" discussions when it hasn't been properly established that Archaeopteryx flew, or if so, how, when, where, and why?


Scott Hartman Science Director Wyoming Dinosaur Center 110 Carter Ranch Rd. Thermopolis, WY 82443 (800) 455-3466 ext. 230 Cell: (307) 921-8333

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-----Original Message----- From: Tim Williams <twilliams_alpha@hotmail.com> To: dinosaur@usc.edu; mhabib5@jhmi.edu Sent: Sun, 15 Jun 2008 8:27 pm Subject: RE: vaulting pterosaur launch, questions



Michael Habib wrote:


Actually, the degree
to which most paleontologists (and even just biologists in general)
misunderstand running launch has been quite surprising to me. It is
not really a method of improving launch speed or power - running
launch
mostly shows up in birds as a method of dealing with take off from
compliant surfaces (ie. water).


That's interesting, Mike. You could probably count me among that number,
because I thought a running take-off was considered almost canonical for early
birds (such as _Archaeopteryx_, for example). This was an issue addressed (and
redressed?) by Burgers and Chiappe....



Burgers, P. and Chiappe, L.M. (1999). The wing of _Archaeopteryx_ as a primary
thrust generator. Nature 399: 60-62.



First p'graph: "Since the late 1800s, the debate on the origin of flight in
birds has centred around two antagonistic theories: the arboreal (take-off from
trees) and cursorial (take-off from running) models. Despite broad acceptance
of the idea that birds evolved from bipedal and predominantly terrestrial
maniraptoriform dinosaurs, the cursorial model of flight origins has been less
successful than the arboreal model. Three issues have contributed to this lack
of success: the gap between the estimated maximum running speed of
_Archaeopteryx_ (2 metres per second) and its estimated minimum flying speed (6
metres per second); the high energy demands of evolving flight against gravity;
and the problem of explaining the origin of the 'flight' stroke in an earthbound
organism. Here we analyse the take-off run of _Archaeopteryx_ through lift-off
from an aerodynamic perspective, and emphasize the importance of combining
functional and aerodynamic considerations with those of phylogeny.
Our calculations provide a solution to the 'velocity gap' problem and shed
light on how a running _Archaeopteryx_ (or its cursorial maniraptoriform
ancestors) could have achieved the velocity necessary to become airborne by
flapping feathered wings."



Sorry to switch focus from pterosaurs to birds, but how do you picture
_Archaeopteryx_ getting itself airborne from terra firma? By leaping from a
standstill off the ground?



Proximal lever is shorter, distal levers are long. Having a short,
stout humerus is key: it allows for massive bending and torsion
resistance, which is pretty key for a massive quad launching animal.
Note that big birds have short, stout femora for the same reason (but,
again, the role is moved to the hindlimb because birds are obligate
bipeds).


Nice point. Also, birds have shifted stride generation from the hip to the
femur, as part of the forward migration of the center of mass (a flight
adaptation). As such, the more-or-less horizontally oriented femur is exposed
to a lot more stresses than a femur that is oriented vertically (as in non-avian
theropods). Hence, femur of birds is short and stout, to resist these forces.



Refs:


Carrano, M. T. (1998). Locomotion in non-avian dinosaurs: Integrating data from
hindlimb kinematics, in vivo strains, and bone morphology. Paleobiology 24:
450-469.



Farlow, J.O., Gatesy, S.M., Holtz, T.R., Jr., Hutchinson, J.R., and Robinson,
J.M. (2000). Theropod Locomotion. Am. Zool. 40: 640â663.



Gatesy, S. M. (1991). Hind limb scaling in birds and other theropods: Implications for terrestrial locomotion. J. Morph. 209: 83-96




Cheers

Tim


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