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Re: pterosaur femora sprawl



Since most bats typically neither run nor walk, perhaps they (vampires secondarily excepted) basically have no gait.

Interesting thought. I'd say that they have a climbing gait, though (I forgot to include that before in the definition of possible gaits, my fault). Pteropodids, for example, are essentially quadrupedal suspensory climbers, and that should count. But yes, bats are odd. That's why they're fun to work on!


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.

Absolutely, molecular trees have their own problems. I'm just cautioning against firm statements where they are not yet warranted - you originally stated that civets and bats are close relatives, as if it were a certain relationship. What you meant, of course, is that your tree places them there, specifically. You might be right on target, but I'd also suggest being more open to the uncertainty of the situation. That's just par the course for phylogenetics.


If you're using your hands pressed against the substrate to locomote, your hands have no opportunity to become oversized, foldable flying organs.

Why is that? After all, the rules of macroevolutionary trends are not the same as individual daily-use. Seeing as how bats and pterosaurs have/had dual-use forelimbs, how can we be certain that the limbs didn't evolve that way in the first place?


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.

Ah, but I said that they could *facultatively* launch bipedally. That is, quad launch was probably the norm for small, primitive pterosaurs, but they were not limited to using only a quad launch simply because their required launch speeds were not very high. I was referring to the "normal" mode of launch in the sense of day to day activity. That is, a given small-bodied, early pterosaur would normally launch with all four limbs, but might sometimes use only the hindlimbs if need be.


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.

I'm working on it; don't want to do a sloppy job, after all. Feedback always appreciated.


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.

Yes pterosaurs have reasonably large thigh muscles, but they have much larger muscles associated with the forelimb and pectoral girdle. The bone strengths are also vastly different in the forelimb and hindlimb, which further supports this trend. The ratio of bone strength between the humerus and femur (strength in bending, that is) for Anhanguera is 56 times the same ratio for an albatross. If pterosaurs were bipedal launchers, like birds, then the ratio should actually be smaller in Anhanguera (given it is larger than an albatross). Remember, the hindlimbs are still involved in the quad launch, they just generate less power than the forelimbs, and the forelimbs leave the ground last.


Also, vampires have reasonably large thighs and strong femora relative to other bats. Their femora are not the strongest among bats, which indicates that hindlimb strength is not the only critical factor in terrestrial mobility for bats (see Riskin), but several studies (including my own dataset) show that vampires actually have elevated strength in the femora as well as their humeri. However, the humeri are still much stronger than the femora - pterosaurs match this trend (they have good, strong hindlimbs, but much stronger forelimbs).

In terms of parsimony, quad launching does not require pterosaurs to change gaits for launch - we know they walked quadrupedally, so switching to a bipedal launch dynamic is actually less parimonious. Phylogenetically, it's still uncertain - there might have been an early shift to quad walking (and, as Jim and I suggest, quad launching), assuming the ancestors were bipeds, or quad gaits might be basal for the group. Either way, it's a single, fairly simple shift on the tree, so phylogenetic parsimony is probably not the best way to judge the likelihood of the proposed launch system. It's really a mechanics problem - we can detect what the animal's were capable of (and their likely locomotor behavior) using structural mechanics. Of course, we need the phylogenies to determine things like timing and convergence.

Nyctosaurus too?

I suspect that Nyctosaurus quad launched, yes, though with rather less power and speed than critters like azhdarchids (which had power-house builds).


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?

There will be illustrations made available. In terms of pterosaur sister-taxa, I'd be convinced by the typical means - if the proposed sister group (Sharovipteryx and allies) repeatedly falls out next to pterosaurs within the analyses of various authors using a variety of character sets. Quantitative support systems also help, of course. And, of course, the characters in question can make a difference, but this can be very group specific - synapomorphies like feathers can be unusually compelling, for example. Hard to say what this would be for pterosaurs, but it's a secondary issue (I don't require any sort of silver bullet, nor expect one).


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.

Sounds great; I look forward to the upcoming publication(s). Out of curiosity, what are your strongest and weakest clades in terms of bootstrap and decay analyses?


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.

Finding a single tree is convenient, but actually doesn't say much about accuracy one way or the other. Sisters should "look alike" from a character standpoint by definition - I assume you mean in a broad, qualitative sense. That's interesting, as it suggests low levels of predicted convergence, but it also doesn't say much about accuracy, per se. It could mean, for example, that some homoplasy is being missed.



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