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Re: Pterosaur.net



> I'm sure we don't want to confuse young (and old) minds by first saying one
 thing and then its opposite.

 [...]

 "Pterosaur fossils are rare" is found in the same paragraph as "Even
 so, we have thousands of specimens."

 "This makes them unsuitable for fossilisation" is found in the same
 paragraph as "many pterosaur fossils are from exceptionally well
 preserved fossil beds and thus are known with skin, beaks, claws,
 wings and other soft tissues preserved, and not just bones."

You're in very good company in being confused by this, but it is _not_ a contradiction. In spite of containing "thousands of specimens" of which "many [...] are known with skin, beaks, claws wings and other soft tissue preserved", the fossil record still preserves only a teeny tiny biased sample of past biodiversity, and only a tiny part of this ("many" in absolute terms, not out of "thousands") preserves so much as two-dimensional pycnofibers -- none preserves original colors, DNA, soft internal anatomy yadda yadda.

 "Pterosaurs are not dinosaurs (or birds for that matter), but close
 relatives of them. Their exact origins are still uncertain (see the
 origins section)." In the Origins Section one reads, "Essentially,
 much of the information we would look for was lost, so there is
 little to tie pterosaurs to other groups through shared characters.
 This means that it is actually quite hard to see how pterosaurs fit
 in the great tree of life." then "It really boils down to two
 possibilities - the dinosauromorphs (that also produced the
 dinosaurs) or the basal archosauromorphs (that spawned many
 lineages)."

After how much discussion does this follow?

 then "There is not much to chose between them, and even
 many pterosaur experts disagree, but right now the weight of evidence
 falls (just) on the side of the dinosauromorphs." This all seems a
 bit vague,

...exactly as promised in the quotes you give above! :-)

 especially since the origins section includes this note,
 "We can look at their DNA, bones, muscles, physiology and much more.
 Since all organisms (if you go back far enough) have a shared
 evolutionary history, the more similar two species are, the more
 closely related they must be."

Reality is always more complicated. That should really go without saying. :-|

What should not go without saying, however, is the difference between phenetics and phylogenetics. Without any added qualifications, "the more similar two species are, the more closely related they must be" is not a great thing to say.

 All in all it sounds like no one has cared enough or was persistent
 enough, to find the lineage of taxa that really demonstrates an
 increasing number of pterosaur synapomorphies. Seems like anyone,
 even an amateur, could find a lineage that was closer to pterosaurs
 than the vague enigmas that are presented here.

That would be a PhD thesis' amount of work.

 the two studies that claimed to figure this out once and for all

Did they make such a categorical statement?

 Too bad that study also failed to find a distinct
 lineage of proto-pterosaurs.

Here you go again, overestimating the completeness of the fossil record -- and our current sampling of it -- by several orders of magnitude. We have no reason to expect that a transitional series (as known for the origins of whales, limbed vertebrates, birds, mammals, and a few others) should be already known. If people fail to identify one, that could well be because they haven't looked in the right places; but it could just as well be because there just isn't any in collections yet.

 "On the ground the ârhamphorhynchoidsâ were probably pretty poor.
 Their large rear membrane would have shackled their hindlegs together
 making walking difficult, and the shape of their hips and upper legs
 meant that could only really sprawl and not walk upright." Wait a
 minute! This doesn't make sense. The plesiomorphic condition is
 "unshackled," no matter which ancestry one chooses. Perhaps there was
 a misidentificat in the uropatagia(um)? Maybe it was more like the
 unshackled Sharovipteryx?

In the "shackled" condition, how broad was the (cr?)uropatagium mediolaterally? If it was broad enough (and the legs were spread in flight), it wouldn't have hindered walking at all unless an obstacle got between the legs. Is there a fossil that specifically demonstrates a narrow (cr)uropatagium?

 "Eggs were probably laid a few at a time and buried in nests..." If
 buried in nests, were these made of mud, sand or leaves and sticks?
 If they were buried, how did the eggs end up being covered in
 volcanic ash (Wang et al. 2004) or flood sediments (Ji et al. 2004,
 Chiappe et al. 2004)? Why didn't they just stay buried where momma
 put them?

Floods tend to wash soil away, complete with the eggs in it.

 And if buried, why did they have eggshells thinner than any
 known archosaur? -- As thin as lizards that retain their eggs until
 just before partuition?

Lack of a calcareous layer in the eggshell is plesiomorphic. A thin calcareous layer is plesiomorphic for archosaurs, being found in crocodiles; it also occurs in some turtles. A thick calcareous layer is limited to some turtles, geckos, and dinosaurs. AFAIK the pterosaurian condition is rather crocodilelike.