[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: pterosaur femora sprawl



Why not? If they are...(even upside down) they are! Don't expect them to walk bipedally though.

I don't consider resting pose to be a gait. When I use the term bipedal I refer to running or walking. So yes, bats hang in a "bipedal" fashion. But, since is is not a locomotor gait, and given that the hind limbs are not adapted to bipedal walking, I find your assumption that "bipedalism" was important for flight evolution in bats a bit odd - if you're correct about the "freeing" of the forelimbs, then only having them freed while sleeping seems insufficient.


Bats are civets. So are Ptilocercus and dermopterans, according to cladistic analysis. They haven't been tested against each other yet in dna tests.

According to your phylogenetic reconstruction, yes. But there are several competing cladistic analyses. You admit yourself that molecular support has yet to be gleaned - what if that differs?


No problem there. Same with humans. Same with 19 lizards capable of bipedalism. Same with pterosaurs. I have no doubts that Sharovipteryx and Longisquama bellied up to some tree trunks too.

Ah, but even facultatively bipedal lizards actually use the hind limbs for a true gait (ie. sprinting). Maybe pterosaur ancestors did the same thing - I'm not saying they didn't (though I see no reason to assume that they did, at present). However, I doubt that bat ancestors did.


BTW, don't forget, bats climb with their thumbs -- also a departure from tetrapod norms. So, probably secondarily adopted.

Actually, I suspect the departure comes from the lack of use of the other four fingers in climbing. Same effect, different polarity.


In fact, bats have
essentially arboreal limb proportions and structural strengths
(especially pteropodids): they are quantitatively like suspensory
primates in the forelimb structure from the shoulder down to the wrist.

No problem. So are humans.

Humans actually walk bipedally, though. My resting position is laying down, but I wouldn't say that I share a gait with squamates. Again, I agree that the hanging adaptations in bats are important, I just fail to see why they are necessary for the evolution of wings.


Not true. Sharovipteryx, a pterosaur relative, would disagree with you. And when you repair the pterosaur stance, aligning all the axes, bringing them back into more typical tetrapod configurations, then you'll see the shoulder glenoid is aligned above the toes, as in birds, the pelvis is elongated, as in birds, the tarsus has a nice trochlea, as in birds, and you'll see that pterosaurs, especially the early ones with short metacarpi, were fully capable of hind limb launches.

True, a small pterosaur could facultatively launch bipedally. However, I see no reason to expect that this was their normal mode of launch. Quad launching would be more effective for them, and their structural scaling patterns demonstrate that quad launching is the more likely standard method for nearly all sizes of pterosaur - thought it only becomes the obligate state at large sizes.


.Bennett followed von Huene is proposing a hind limb leaping arboreal origin for pterosaurs. That has not been disputed in print.

True. Note that animals can leap quadrupedally, though, and this has little effect on his overall model. I think hind limb leaping was assumed because the bipedally launch model has been intrenched for a while.


I know J. Cunningham is fond of the forelimb launch in Q. but he or anyone else has yet to put a storyboard together on how this happens. I'm curious as all get-out to see it too. Not saying it doesn't happen, but if so, it was not the ancestral way.

Jim is not alone in this; I have a paper in press on the structural evidence for quad launch in pterosaurs, and have more on that in the works (he and I came to the same conclusion, separately, through different means some time ago). I'm not sure what you mean by "storyboard", but if you mean the launch kinematic, then Jim actually has worked it out, as have I (though Jim worked it out in more detail, and prior to myself). Quad launch was almost certainly not limited to Quetzalcoatlus. The structural strength ratios, body size trends, walking stance, muscle builds, and trabecular bracing of pterosaur long bones all indicate that most species quad launched as the primary take off dynamic. Small species could facultatively launch bipedally, if need be, but quad launch would be more rapid and efficient. I suspect, therefore, that quad launch was basal to pterosaurs proper. That said, if the nearest relatives of pterosaurs do turn out to be bipedal, then it may be that the ancestral state (in the stem group) was bipedalism, as you indicate. At present, I am not convinced that this must have been the case, and if it was then the switch to quad walking/climbing and launching occurred very early in pterosaurs.


Are you referring to branch support methodologies?

Yes and beyond. Whatever you want to throw at them.

Fair enough. In that case, what branch support algorithms have you used so far? What sort of nodal support do you get? Have you done any sort of sensitivity analysis regarding character assignment/use?



Cheers,

--Mike


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