Re: Testing competitive exclusion in birds, bats and pterosaurs

[Michael Habib <mhabib5@jhmi.edu>]

> 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.
> JimC

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.

Cheers,

--Mike H.