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



don ohmes wrote:

I already pointed out the error, which is failing to consider the various points of various glide sequences at which selection on incipient flapping can occur. Nothing to do w/ falsifying equations.

That's the different issue from the one which I was addressing. The point was simply that the required set of ancestral traits for arboreal flight origins may be more strict than it appears. Or, to be more specific - assuming that bats did indeed have gliding ancestors, it is still quite likely that living gliders (like flying squirrels and possums) are not good analogs, in part because the gliding mode and planform of animals like flying squirrels produce mechanical limitations to flapping.


I know of no successful attempt to falsify either route, including the current "bird evolution cannot be gravity-driven because they are not purely arboreal in origin" attempt, which is itself falsified by the fact that early birds could have readily utilized trees in the way I describe.

I tried to falsify arboreal origin years ago, and failed. Ditto ground-up. Concluded it couldn't be done ("way too hard"), and am very skeptical of claims to the contrary. It is all 'best guess', afaik. But it is fun to falsify the attempts to "solve" the mystery.

It's better than best guess, but not definitive, either. The evidence that we have for birds indicates a strong terrestrial component to flight origins. That does not eliminate any possible arboreal component, but it does contrast with bats, for which evidence suggests a strong arboreal component. This difference appears, as best we can tell, to be real and notable. To that extent, the various models are testable. More specific scenarios, while fun, are largely speculative and probably not very informative. Especially if they try to make assumptions about the magnitude of selection coefficients (estimating sign is a bit more reasonable).


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