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

[Dinogeorge@aol.com]

In a message dated 9/26/99 5:42:50 PM EST, mbonnan@hotmail.com writes:

<< I think we really should think 
 about the more powerful hindlimbs in archosaurs as a necessary exaptation 
 for becoming bipedal on the ground first.  In most mammals, the forelimbs 
 carry more weight than the hindlimbs, so perhaps they were constrained by 
 this and weren't able to become bipedal as often?  And, I have never once 
 said bipedality was an "improvement" over anything.  Perhaps it was the only 
 way for dinosaurs to move appreciably fast on the ground? >>

I have previously suggested that development of strong hind legs would help a 
grounded dinobird with flightworthy wings to take off by running without 
having to climb back into a tree first. This seems sufficient reason for 
dinobirds to develop strong hind limbs, bipedal stance, and fore-and-aft leg 
articulations, and probably accounts for the prevalence of strong running 
legs throughout the theropod-bird clade. But without the wings, I see 
absolutely no compelling reason to acquire bipedality and some pretty good 
reasons not to. Most mammals run wonderfully well on all four limbs and never 
in their evolutionary history preferred bipedal stance to quadrupedal. Ditto 
most nonavian reptiles, amphibians, etc.