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

Re: pterosaur femora sprawl



MHabib wrote:
> 
> 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.

Since most bats typically neither run nor walk, perhaps they (vampires 
secondarily excepted) basically have no gait. Essentially they fly and rest. 
They are different from most tetrapods since they do not use their manus palms 
down to locomote on substrate. It is a bit odd. And aye, there's a phylogenetic 
behavioral trail to follow as well with a big gap right at the beginning of 
bats, but not as big as previously assumed (paralleling the false mystery of 
pterosaur orgins).
> 
> > 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 competing studies include civets and Ptilocercus. That's why they're all 
running into brick walls. What if blood tests differ? Well, let's put it this 
way, we'll follow all the clues and use parsimony. DNA tests are contradictory 
with regard to reptile relations. So, dna tests are not perfect. Let's just get 
it right, no matter the path taken. I'm just shining a light where none has 
shone before, no big deal.
> 
> > 
> 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.

Previous to the point that bats became inverted, bipedal and perhaps 
essentially immobile while attached to tree limbs and cave walls, their civet 
ancestors would have been mobile and had a true gait. Then, closer to bats, 
they didn't. There was a cut-off point. Frankly, I don't have a clue as to 
_exactly why_ bat hands became wings. Fossils and living taxa just tell us what 
happened before and after.
> 
> >
> 
> 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.

If you're using your hands pressed against the substrate to locomote, your 
hands have no opportunity to become oversized, foldable flying organs. Case in 
point: Dermopterans and flying squirrels (convergent membranes, not homologous) 
have smaller grasping hands because they did not have a bipedal phase. 
> 
> > 
> 
> True, a small pterosaur could facultatively launch bipedally.  However, 
> I see no reason to expect that this was their normal mode of launch.  

If primitive pterosaurs were small and launched bipedally, that, by definition 
is the normal mode. Anything deviating from that norm is derived.

> 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.

Please, Mike, this I have to see. I will even animate it, once I have the 
stages involved as I have animated walking and landings before. I'm fascinated 
by the possibility and eager to explore your theories, but if I see a reason it 
can't or has trouble working, I'll let you know. Pterosaurs have big thighs, 
great for launches. But vampires use their forelimbs, so let's see which model 
is more parsimonious. Don't keep me in the dark.
> 
> >  .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.

As you know, Bennett, for simplicity perhaps, illustrated only the launching 
hindlimb of Dimorphodon. He did not expound on the use of the fore limbs during 
launch.
> 
> > 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).  

Yes, this is what I want to see -- as you see it.

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.  

Nyctosaurus too?

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.

Yes, very early in pterosaurs. All pterosaurs except one were able to touch the 
ground while standing erect in the bipedal configuration (glenoid over toes), 
most with elbows bent, some not. The exception, naturally enough, is the most 
basal pterosaur. 

Please send some drawings whenever you can. Jim has had the same request for 
awhile. And what would it take to get you to be convinced that there are no 
known closer relatives to pterosaurs than Sharovipteryx and kin? 
> 
> >> 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?

Bats? or Pterosaurs? In either case I've used heuristic and bootstrap 
algorithms with high 90s and 80s except where taxa are known by skulls only or 
without skulls. I employ various decay analyses, deleting taxa, characters, 
randomly, non randomly all with confirming results. Unlike prior workers, I get 
a single tree. One in which sisters look alike. Speaking of which, no prior 
pterosaur analyses discuss the issues you raise.

Best regards, David.

> 
> 
> 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