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Re: pteros have lift-off

David Peters wrote:

I see storks and herons taking off from a standing start, perhaps using ground effect before gaining cruise speed. There's no 30º trajectory there.

Storks and herons may use a bit of ground effect in certain conditions, but they don't generally require it. They take off at steep angles owing to specifics of limb morphology and very low wing loadings (and reasonably short spans). The difference in launch angle isn't all that informative here - it just indicates that a pterosaur probably didn't look much like a heron taking off. They're not built like herons, so that's not surprising. It seems that pterosaurs were built to launch fast and powerfully, but not especially steeply (with perhaps some exceptions in the smaller body mass ranges).

Do your figures take into effect 'ground effect' flying?

I don't usually bother, though the calculations could be made more accurate by doing so. Ground effect will not allow large pterosaurs to launch bipedally, though. The effect is insufficient in magnitude to solve the problem at hand (that much I have confirmed, at which point I usually just leave it out).

I mapped sequential photos of a pelican taking off (I can send this via a non DML email). Although the pelican is airborne immediately, the acceleration over a half dozen frames is easy to measure while flying in ground effect. Maybe, like pelicans and herons the availability of ground effect means pterosaurs don't have to reach cruise speed within a second after take-off? Perhaps a trajectory in big pteros lower than 30º would be equivalent (i. e. ultimately leading to flying at cruise speed)?

Ground effect doesn't help quite that much. Besides, a biped launch doesn't get many pterosaurs even close to cruise speed - they need to get at least close enough for an anaerobic burst window to finish the job. And there remains the lingering issue that pterosaurs are so well built for quad launching and so poorly built, as a general rule, for biped launching.

Looks like: 1) crouch simultaneous with wing unfolding and upbeat. 2) hindlimb extension simultaneous with first downbeat. No surprises. Probably common to most birds.

The hindlimb impulse precedes the production of most of the aerodynamic force production - at least, that's true for all birds so far tested explicitly.

So, I'm gathering from the video that a large amount of thrust is generated by the wings along with thrust from the hind limbs. Which seemingly relieves the hindlimbs of a large amount of duty -- which was a major concern of yours.

The wings do not produce much launch force - that is the real kicker here. As David M. correctly ascertained, about 90% of the launch force (in birds) comes from the hindlimb impulse. The wings are not traveling fast enough to generate much force. Even hummingbirds, with their tiny legs, produce 59% of their launch force from the hindlimbs (see work by Tobalske).

The upshot of this is that hindlimb skeletal strength scales very rapidly in birds - such that large species have disproportionately strong femora. The humeri scale much more slowly, by comparison. Pterosaur scaling patterns are literally reversed.

And this is incompatible with small and large pterosaurs because...?

See above - it is incompatible because most of the launch force needs to come from the initial leap, and the comparatively gracile hindlimbs in large pterosaurs are insufficient to carry the loads. Smaller species are more uncertain - biped launch isn't absolutely forbidden, but there is no good evidence for it, while the structural scaling patterns and forelimb morphology of most small taxa continue to indicate quad launch adaptations. Lacking any positive evidence for bipedal launching, the most simple model at present is that even small species preferred a quad launch. It appears to be required for big guys.



Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280 0181 habib@jhmi.edu