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Re: Testing competitive exclusion in birds, bats and pterosaurs

Birds developed the specializations for marine soaring flight within 5 million years of the demise of pterosaurs (different requirements from terrestrial soaring). I think a speculative case could be made that pterosaurs may have been excluding birds from this niche.

It does seem quite suggestive, especially given that pelagic birds apparently existed throughout much of the Cretaceous, but no lineages (that we know of) generated large-bodied soarers until after the K/T.

Note also that there is still no consensus that all or any pterosaurs had a wing-hindlimb connection.

Good point. I think morphospace analyses of pterosaurs (like the one referenced at the start of this thread) sometimes confuse the results of quadrapedal terrestrial gaits (and their subsequent constraints on limb proportions) with evidence for a wing-hindlimb connection.

A universal wing-hindlimb connection in all species implies that pterosaurs were specialized for terrestrial soaring. Unusual in animals that seem to have been mostly fish eaters.

In addition, the planforms proposed for wings connected to the hindlimb in pterosaurs tend to be poor even for a terrestrial soaring form, with both the estimated loadings and aspect ratios often falling well below those seen in living dedicated thermal soarers. Living raptors and storks do not have wings nearly as short and broad (nor masses as low) as some individuals seem to expect. After all, living inland soaring birds use a number of sources of lift other than thermals, many of which are better extracted with greater spans and/or higher loadings. Such species also have to travel between lifting sources at a reasonable rate. Not to mention that the largest pterodactyloids would be seriously pushing the limit with regards to being able to stay within a narrow thermal ring, simply by virtue of total span. Cloud streets would be much more useful to an animal that size, and I expect that extracting energy from cloud streets would usually select for a narrow chord planform.


--Mike H.