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Re: Fw: Dinosaurs and birds

Thanks for the tip.  This was one of my sources...

http://darrennaish.blogspot.com/2006/05/pterosaur-wings-broad-chord- narrow.html

Ah, yes, I've read that post as well. Darren Naish is a really sharp guy, and he writes very well, but I think he may have missed a couple of items in that particular assessment. For starters, the The Crato Formation azhdarchoid specimen SMNK Pal 3830 does not show much about the patagium at all. If you look at an uncropped photo you'll see that the section of patagium actually just passes under the hind limb altogether. It is either just a completely detached piece of wing , or it is a flipped section of uropatagium (which is what I think is going on).

That leaves the apparent phylogenetic bracket unbounded, such that we have a few "rhamphorynchoids" like Sordes that seem to have broad chords, and some others (like rhamphorynchids) seem to have quite narrow chords. This leaves very little information about derived pterodactyloids. I've actually talked to Darren about some pterosaur mechanics, and I don't think he's actually particularly dead set on wide chords for all pterosaurs (though he'd have to confirm that).

A few authors have found a correlation between forelimb and hind limb lengths in pterosaurs, and suggested that this indicates a continuous patagium. This is likely a constraint related to quadrapedal terrestrial locomotion, instead.

The expected situation (at least from my point of view) is that the planforms of pterosaurs would be efficient for their habitat and associated flight dynamic, just as in modern flying animals. Species in cluttered environments, or small bodied species that hunt insects, would be expected to have wide chord wings. Pelagic species, which are the vast majority of pterosaurs, would be much better served by high aspect ratio wings and independent flight surfaces. Large-bodied pterodactyloids, in general, would probably be most efficient with high aspect ratio wings free of the hind limb, even those that lived inland. There are a lot of common misunderstandings about flight dynamics, especially soaring flight. I think some of these have heavily influenced the preference for continuous flight surface models among some pterosaur workers.


--Mike H.