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re:Betty's question regarding stiff tails



     >Gatesy has shown that in dinosaurs, due to their vertical femora, the 
     >tail must have been pulled down with every extension.  So lateral 
     >undulations did not occur in dinosaur tails during locomotion, only 
     >perhaps in corrective weight shifts to maintain balance during 
     >moments of instability.    -David Peters
     
     __________________________________________________________________
     
     
        So what you're saying is, the tails had more up-and-down bounce 
     with each step, rather than side-to-side movement? 
        Does Gatesy mean by extension, the full-stretch of the leg towards 
     the rear of the animal, AWAY from the head? (in animation the 
     EXTENSION is the name of the move of the leg as it reaches forwards, 
     before contact with the ground during the step, not the relaxing of 
     the leg as it leaves the ground during the step.  The other direction 
     entirely)
        Does Gatesy suggest that the tail bend DOWN to the ground in a 
     straight teeter-totter/see-saw movement?.  That seems very awkward.
       Wouldn't the flexibility of the tendons that Tom was describing lend 
     to a more accordian-like bend of the tail to the diagonal-down-side? 
     If the left leg moves forward, the tail seems to move more naturally 
     to the left and above the plane of the body(this is in weight-shifts 
     only; I haven't seen the way the tendons work from other angles than 
     the side). 
        So for each step, the tail would rise above the plane of the body 
     (the hip rotates, right?  Wouldn't this rotate the tail above and 
     below the plane just by itself?).  The tail would be pulled forwards 
     and up at the hip-meets-tail-point by the skin and tendons along the 
     side of the leg moving forwards, and since the reverse leg would be 
     doing the opposite movement, it would then check it's movement to the 
     side by the tendons and skin from the other side, and move to the 
     other side and mirror the movement during the next step withthe otehr 
     leg.
     
     Sort of like this:
     
     showing hip movement only             showing tail movement only:
     .
     . /\     ___=___                          [----=----]  
     .       ( \   / )                         [     ()--]               
     .          \ /      \/             /\     [    ( )--]
                                        ||    [    (  )--]
     left leg moving forwards           ||    [   (  )--]
     right leg moving back              ||   [  (   )--]
     -showing hip rotation around       ||   [ (   )--]
     .pivet of spine(=)                 ||   [(    )-]
     .                                  ||   [(____)]
     .   (from the back looking         |
     .     towards the head)             weight of tail being pulled        
     .                                   forwards by forwards extensions of 
     .                                   leg
     .
     
     The rotation of the hips seems like it may be reversed, now that I 
     look at it like this.  On humans, the hip sway counter-balances the 
     upper torso, the weight directly ABOVE the hips-this is to keep 
     everything balanced OVER the leg bearing weight, however dinosaurs 
     didn't HAVE any weight above the hips, just fore-and-aft of it, so 
     would the hip rotate counter to how it does in humans?   Grrrrk, now 
     I'm really confused!
     
     -Betty Cunningham
     (bcunning@nssi.com at work)
     (bettyc@flyinggoat.com in the studio)