Re: Aquatic Origin of birds (was Aquatic spinosaurs (was Size of *Neoceratodus africanus*))

[Mike Habib <habib@jhmi.edu>]

On May 3, 2009, at 10:40 PM, Amtoine Grant wrote:
> Correct me if I'm wrong, but weren't the earliest specimens of  
> Archaeopteryx found in aquatic  deposits from ecosystems relatively  
> devoid of trees? Factoring in Archie's crocodilian/spinosaurid-like  
> (pisciviorous?) conical-esque teeth and the possible non-feathering  
> of the humerus, this theory is only held back ever so slightly by  
> the fact that the tail was already fully feathered.

The aquatic origins hypothesis is interesting in some ways, but  
doesn't have much going for it, at this point.  Among the problems it  
faces is the fact that Archaeopteryx has neither the hindlimb  
structure nor the forelimb structure that one would expect in a diving  
taxon (that is, it does not possess hindlimbs adapted to hindlimb  
propelled swimming, nor forelimb spars indicative of forelimb- 
propelled swimming).  The only thing that is at all "aquatic" looking  
in Archaeopteryx, by modern standards, is is relatively thick  
appendicular cortices and lack of appendicular pneumaticity (these go  
hand-in-hand).  That, however, appears to be plesiomorphic for  
Archaeopteryx, and so does not mean the same thing as the secondary  
reductions in pneumaticity seen in living diving birds.

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