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Re: pterosaur femora sprawl



> 

> Bats hang, sure, but I wouldn't call them bipedal.  

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

And we don't have 
> enough information on their ancestry (given the enormous range of 
> competing phylogenetic hypotheses on bat origins) to gauge what the 
> ancestral state was.  

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

Besides, even though bats rest while hanging from 
> the hindlimbs, they climb quadrupdeally.  

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

> 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.

>   It only diverges greatly from arboreal expectations in the hand 
> (Swartz and Middleton, 2008). The bat hindlimb is actually quite 
> unsuited for bipedal locomotion - the rotated femoral head makes for 
> good hanging but poor walking.  

Nobody ever said 'walking.'  That's a 'thought cloud' you can dispense with. 
With bats it's all about hanging.

>They're really quite locked into quad 
> walking now.  That doesn't mean that their ancestors were quad walkers, 
> but I do fail to see why we should assume a bipedal intermediate 
> (especially given that none of the potential outgroups to bats are 
> bipedal).

No, there ancestors were quads, until they became sit and wait predators. Bat 
torpor stems from that phase. 
> 
> I also note that launch mechanics suggest birds as the only volant 
> group with bipedal ancestry: bats launch quadrupedally (if they can 
> launch from the ground at all), and pterosaurs very much seem to have 
> done the same.  Birds are therefore the only one of the three that use 
> a hindlimb dominated launch initiation.

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

> 
> The phylogenetic argument is stronger: if you're correct about the 
> placement of pterosaurs, and their immediate outgroups are bipedal, 
> then that would at least partially suggest bipedal ancestry.  However, 
> I'm a bit confused on your last point: how is it that your favored 
> outgroups can be said to be objectively closer than those favored by 
> other phylogenetic hypotheses?  

When one includes Langobardisaurus, Cosesaurus, Sharovipteryx and Longisquama 
with pterosaurs and any other putative sister groups, be they Scleromochlus, 
Marasuchus, dinosaurs, or whathaveyou in cladistic anlaysis, those four genera 
always come out closer to pterosaurs, and for good reason! Anyone can test this 
for themselves, using any readily available cladogram, characters and taxa.

Are you referring to branch support methodologies?

Yes and beyond. Whatever you want to throw at them. The important thing is 
taxon inclusion, rather than prejudicial exclusion, which has been the 
pterosaur legacy. That dang antorbital fenestra!

Best,  David Peters
> 
> 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