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RE: Limbs and niche partitioning

Attempting scientific discussion on the dinolist, Matt Bonnan wrote:

>  In other words, maybe one of the problems with getting 
>  huge is that if you have multiple degrees of freedom in your joints, you 
>  have problems going beyond a certain size because of all the torques, 
>  stresses, etc.  If you are ancestrally constrained, perhaps it is easier
>  for you to get big?
        I don't know where he got it, but this is similar to the position
adovcated by Sankar Chatterjee in our Vert Paleo class at Tech. He argued
that the cylindrical femur head was good for supporting weight...

Nick Pharris wrote:
>This may also be why dinosaurs were not particularly effective at producing
>small-mammal-sized forms [...], since flexible limbs and 
>spines are probably more effective than dinosaur-type limbs and spines for 
>skittering along the ground and in the trees.
        ...Yeah, Chatterjee was with y'all on this too. he pointed out that,
at smaller sizes, terrain is far more irregular. A pebble is not a big
obstacle for us; if it is small enough, the flesh on the bottom of our feet
will conform to it. For a mouse, a pebble is a hurdle that has to be
negociated. Now imagine you are a small bipedal archosaur with femora
constrained to parasagital motion. Might be pretty hard to get over that
there obstacle. It might be one thing if you are a growing juvenile, and a
little more rough-and-tumble, growing reasonably fast and possibly relying
on your parents to lift you over rocks (do you suppose cartilagenous joint
surfaces helped?). But, do you think these guys would be able to compete
against mammals?

     Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
  "Why do I sense we've picked up another pathetic lifeform?" - Obi-Wan Kenobi