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David Peters wrote:

I see arcs that must not intersect the ground. Pterosaurs had a huge arc to pass, one way or the other, as they started with hands on the ground at the zero point on the graph. Granted, there ought to be more bounce when quad, but is it enough?

If it isn't enough, then biped launching is going to be even worse. My calculations thus far indicate that quad launching gives plenty of clearance but biped launching does not. I could be wrong, but I haven't seen any structural or kinematic data to indicate otherwise. Either way, ground clearance is certainly an important factor, and one that I watch for, as well.

In the meantime, I always encourage nonbiped believers to go check out this site with movies of treadmilling lizards -- none of which are as good at this as basal pterosaurs were for a whole raft of anatomical reasons. But dang they're fast. And with that kind of rocket-like speed, maybe launching was different than has been imagined. With the hands off the ground, strange things can happen.

They are indeed fast. Some quadrupedal lizards are even faster. Unlike pterosaurs, though, bipedal lizards (or rather, those that run bipedally) do not have extremely gracile hindlimbs and super-strong forelimbs. This also goes back to the basic issue of leaping vs. running launches - namely, that running speed is probably much less of a factor here than leaping performance. Sweet videos, though, regardless.

Also, as in most things pterosaurian, we can't over-generalize. What was good for one, may not have been good for another due to the wide variations in plan and size.

True. So far, quad launch seems to be the best fit for just about everything I've analyzed (which includes azhdarchids, ornithocheirids, pteranodontids, anurognathids, and tapejarids). For anurognathids, both biped and quad launches work, but quad launch gives better performance, and there are a few forelimb traits that suggest it was the primary launch mode. There is one species of mid-sized pterosaur that might have been an exception, but still working on that. So, while generalizations are dangerous, I'd argue that a good starting point is helpful. In this case, my argument is that starting with the position that most pterosaurs were quad launchers is probably the better option, at least at the moment. We may then find some exceptions to the trend as time goes along (which would be nifty in and of itself).



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