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

["Matthew Bonnan" <mbonnan@hotmail.com>]

Dinogeorge says:
> 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.

Again, here I disagree.  Breaking a leg is a bad deal for most animals, and 
because it tends to hinder their food collecting abilities and makes them 
more susceptable to predators, I don't see what the difference is.  
Historical constraint on body form may ultimately be what determines the 
likelihood of bipedality arising in a group.  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?

Furthermore, Dinogeorge added:
> 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.

I'm sorry I use "perhaps" and "may," but I would never assume that I knew 
100% this was the way something was.

Are not the boney articulations constraints?  You can only put the bones 
together so many ways, and of those, only certain angles and articulations 
make sense.  I don't think I've said anything here about the bones 
themselves where one could say "perhaps" or "maybe."  You put the bones 
together, they only fit certain ways, you constrain what's going on.  In 
many of these dinosaurs, the only way to get the freedom of movement you see 
in the arms and legs of mammalian tree-dwellers (or descendants thereof) is 
to break or dislocate the bones.

I'm telling you this because I want to know, with such stiff limbs, how such 
animals are walking around in the trees, or how such animals show clear-cut 
evidence that they were descendants of tree-dwellers.  Just being bipedal 
won't cut it for me, not in light of what I know about the boney anatomy of 
theropods.

You may not think so, but I'm giving your hypothesis a fair chance.  I'm 
asking you, show me why you think this.  Again, let's forget about 
cladistics and systematics methodology and just show me some definite 
characteristics in the articulations and bones where I might go, "oh, wow, 
hadn't thought about that, hadn't seen that."

Matt Bonnan

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