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



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