Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)

[Dinogeorge@aol.com]

In a message dated 9/26/99 10:51:01 AM EST, mbonnan@hotmail.com writes:

<< No one is saying bipedality "just happened."  Archosaurians have more 
 powerful hindlimbs than forelimbs.  Perhaps bipedality could evolve under 
 various pressures to run faster by getting the forelimbs out of the way, 
 hence the more reduced forelimbs of the early dinosaurs. >>

I have encountered no hypotheses of the origins of bipedality in archosaurs 
except those that simply take it for granted that it was an improvement over 
quadrupedality. The phrase "improved stance" and the like occur all too 
frequently in these works with no justification. If bipedality is some kind 
of "improvement," show me how. Show me the wealth of animals besides birds 
(for which the bipedal stance everyone agrees is plesiomorphic) that employ 
bipedality habitually in their lifestyles. I suspect human paleontologists, 
being bipeds themselves, suffer from "biped chauvinism." Are birds successful 
more because they're bipedal, or more because they're marvelous fliers?

Breaking a leg isn't fun for any animal, quadruped or biped. But at least a 
quadruped has three other usable legs while the broken limb heals; a biped 
has only one. I consider bipedality to be a hindrance that must be overcome 
by compensating adaptations in the forelimbs and other parts of the body. A 
bird with a broken leg can still fly.

There are too many "perhaps this" and "perhaps that" arguments and 
counterarguments in this issue. Not enough constraints to settle the 
question, certainly not enough constraints to reject any reasonable 
hypothesis.