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Re: pterosaur femora sprawl

David Peters wrote:

Which first pterosaurs? No pterosaurs (and I mean _none_) had a shoulder-knuckle length less then their hip-ankle length. 

True. But no pterosaurs walked, bipedally or quadrupedally, with a
horizontal backbone.

I'm not sure how you can know this (is there something I've missed?). In any case, the fore(walking)limb is always longer than the hindlimb. This would result in the backbone on a slope even in the shortest forelimbed critters when they had their hands on the ground.

True. I had Arthurdactylus in my mind's eye when I wrote Anhanguera.

Arthurdactylus has a hindlimb/forelimb ratio only moderately moderately higher at 5.2. That might be in the range of individual variation for Anhanguera.

And you are so right about certain Nyctosaurus, Rhamphorhynchus and
Campylognathoides. In any case the point is relative mass or bulk --
not length -- although length is more readily measureable and
certainly, as you point out, a factor. The pelvis, hindlimb and feet
of ornithocheirids are so small they are dwarfed, in comparison, by
the bulk of the wings, despite their length.

Yes, the mass is more important. The hindlimbs on Rhamphorhynchus look pretty flimsy to me. At least as flimsy (if not more so) than ornithocheirids. Nyctosaurus's hindlimbs are a joke!

Don't forget the albatross and the hummingbird (comparatively small legs). Case closed? : )

The data I have for albatrosses puts their ratio at 4.3-4.4. Eyeballing it, they seem to have much more robust legs than any of the pterosaurs with ratios that high or higher. I don't have anything on hummingbirds.

Now, the point of this argument (I think!) was about whether pterosaurs had the legs for a bipedal launch. Lots of pterosaurs obviously had teeny-weeny legs (shorter and less robust than an albatross), which were probably inadequate as the primary launch mechanism. Derived ornithocheirids are not a special case here, we see it in lot of them.

This works well for the quad launch hypothesis, because puny-legged pterosaurs could still launch in the ordinary pterosaur way. The bipedal launch scenario, however, demands they launch in a special way (diving off cliffs?).

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Palaeontography: http://palaeo.jconway.co.uk