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Re: bauplan convergence



George wrote:

Not just "easier." I think the physics of the situation >completely
precludes< evolution of flight "ground up" in vertebrates. Energy to remain
aloft without already having well-developed, flightworthy wings is simply not
there. This falsifies the ground up hypothesis; drives a stake through its
heart.

Terms like "remain aloft" and "flightworthy" suggest that you already know by what path flight developed. Ah, back again to BCF. Walked right into that one.


If insects could evolve flight from the ground up (or the pond up), why not vertebrates?

<< If the transition from biped to quadruped can happen in the growth series
of
a single species, I see no reason why it should be so difficult to happen
within an evolutionary lineage. Why should it be necessarily "more
difficult" than switching from scansorial to quadrupedal. >>


I'm talking about >obligatory< bipeds, not facultative bipeds here.

Is there such a big difference? In my books, the only difference is that in facultative bipeds the forelimbs can help support the weight of the body (useful for feeding at or near ground level), while in obligate bipeds, the forelimbs cannot (or or are not used as such habitually).


Speaking of quadrupedal dinosaurs - I know Dong Zhi-Ming thought the mid-Jurassic theropod _Xuanhanosaurus_ might be partly quadrupedal. The idea was based not just on the size and robustness of the shoulder and arms, but the design of the manus (which seems to suggest that the fingers were useless for grasping). That was back in 1984. Does anybody have an update on this notion?


Tim ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com