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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)




don ohmes wrote:
Not really. Competitive exclusion is a basic principle, while postulating that mechanical hurdles prevent a passive-to-powered flight transition are not, especially when it is consensus that bats and pterosaurs did it.

Competitive exclusion is indeed a well-established concept in biology, but so is the knowledge of mechanical constraints. Besides, being a "basic principle" does not make a given factor more likely. Competitive exclusion is notoriously difficult to demonstrate, in fact, and it is still uncertain how important it is in determining evolutionary patterns. Personally, I tend to think that exclusion plays a major role in many cases, but that doesn't mean that it gains "throw away" dominance over other explanations - especially when there are other constraints known to be a factor. The mechanical hurdles to which I refer are not mere postulates, incidentally - the specific structure and planform of many living gliders is such that rapid oscillations of the airfoils would have a negative impact on vorticity.


The origin of flight in pterosaurs is currently equivocal. The transition is a bit better supported for bats, but the details are still unknown - it is quite probable (given the morphological evidence) that a glide-to-powered transition occurred in bats, but we can also hypothesize that something about bat ancestors made this transition more mechanically feasible than it would be for many living groups of gliders. We won't know until better fossil resolution is obtained from near the base of bats.

Heh. Although I gather there is a contingent that favors a terrestrial origin for ptero's. Sorry, that was a cheap shot. Anything (almost) is possible.

No worries. Actually, I consider the origin for pterosaurs to be currently equivocal, as do most pterosaur workers. It is completely plausible that arboreality could have been involved - but it didn't have to be.


I note that incipient birds did not have to compete w/ either modern birds, or bats. Or (I assume) mice, shrews, weasels....

They may have had competition from pterosaurs, however (in terms of flying groups), and there were certainly plenty of small endotherms around. There were no mice or weasels, but there were multis and basal therians. Depending on the specific habitats and diets of the basal birds, they could have had numerous potential competitors. The impact on flight evolution is currently difficult to determine.


Heh. Oh, do you have an example of "terrestrial origins for flight"? :D

As mentioned before, birds may very well be an example. Insects might be, as well. Pterosaurs are currently equivocal.


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