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tucking (long)



     >While we're on the subject, and now that the famed Greg Paul is in
     >our midst (Hi Greg!), what does everyone think about the now-common 
     >pictures of theropods (etc.) running with the arms all tucked up?  It 
     >does look kind of cool, but do you think it really happened?  I'm 
     >certain that for aerodynamic reasons, they kept the arms close in to 
     >their _sides_, but I'm not so sure about having them all curled up (a 
     >la bird wings)...
     
     
     Bipeds go both ways in what their extra appendages do when moving 
     upright.   
     
     Humans DON"T tuck their arms while running, we use the swing of the 
     arm to counterweight the leg movements.  We move pretty fast and cover 
     a lot of ground as steady runners.  We are built to run or walk over 
     long distances.
     
     Most other primates rarely walk around on bipedally, but when they do, 
     they swing their arms as counterbalance, OR rock to the sides to aid 
     in counterbalancing.  Monkeys and lemurs usually raise their arms 
     while walking and keep them stiff and out of the way OR rock to the 
     sides, rarely swinging them (usually the ratio of arm length exceeding 
     leg length is a simple explanation)
     
     Basilisk lizards run with their arms tucked straight doun at their 
     sides.  They only do bursts, and the arms are moved out of the way as 
     the "landing" of the lizard is usually abrupt and they need the front 
     legs ready to land on.
     
     Birds that fly as their major means of transportation tuck their arms, 
     their wings don't move from a given position while running.  (You can 
     tell by looking at the feather directions where the wings fold next to 
     the body-the imprint of the wing is a permanent growth-pattern.)  
     Birds that are trying to take off are excluded from this 
     discription.(they hold their arms out)
     
     Birds that don't fly tend to raise their wings up off the back.  They 
     don't flap or rotate the arms at all to aid counterbalancing.  The 
     ostrich and emu may do this to cool the body.  The penguin doesn't 
     flap to aid counterbalancing; I think it's more of a display function.
     
     Bears keep their arms at their sides, while ambling on their hind 
     legs.  If their arms are out for an attack, the arms don't swing, but 
     are sort of held in front of the bear as he uses his weight to fall on 
     his prey.
     
       I believe that animals that are solely dependant on bipedal movement 
     will swing their arms in counterbalance as the final goal of their 
     evolution, as it is a great aid to distribution of weights and 
     balances during locomotion.  Monkeys and lemurs aren't totally 
     dependant on walking or running, as brachiating is their main form of 
     movement.  Birds that run are devolving the use of the wing entirely, 
     and would soon have vestigal remaints of arms (probably just for 
     display purposes).  Penguins swim and the wings are used for that.
     
     Thus:
     large bipedal/quadrapedal dinosaurs such as hadrosaurs which spend 
     some time on all fours grazing (on whatever), would tuck while running 
     on two legs.
     
     large therapods would probably run with arms up out of the way of 
     their feet, stiffly forwards, and in a position where their arms would 
     be out in an attack position (even stumpy T rex).  They probably 
     walked with their arms tucked under their bodies.  The size of the 
     arms in therapods tends to the vestigal sort of paradigm.
     
     medium therapods and smaller therapods, ornithosaurs, coulesaurs, 
     hypsepholodons(sorry, I'm at work-no spelling check for names) all 
     quite probably swung their arms to counterbalance their weight.  The 
     arms were of a significant size to affect weight shifts, and evolution 
     would tend to aid a mechanism that aids in aiding movement.  The 
     shoulder girdles of the ornithosaurs wouldn't allow for much rotation 
     side to side, but plenty from front to back.  Great arm swinging 
     stuff.
     
     Betty Cunningham(Flyinggoat@aol.com)
                     (bcunning@nssi.com)