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Re:Caudo-femoralis remodeling



was:Archaeopteryx or Velociraptors
Peter Buchholz  wrote about the reduction of the tail muscles.
>>When this happened, the caudo-femoralis, which in dinos
was the MAJOR leg mover, lost most of its attachment area, so to
compensate birds etc elongated the tarsometatarsus and enlarged their calf
muscles.
  This is also an explanation as to why big quadrupedal dinos never lost
their big tails.  There is no real reason sauropods needed long tails for
balance or whatever.  They did need them to anchor their leg muscles
though, and there was no real reason to change to the calf dominant bird
style, since the tails of sauropods didn't get in the way like they would
in the branches of a tree.>>
   I also believe that the caudo-femoralis (or is it caudi-femoralis?) was
the major propulsive muscle group in dinosaurs.  Many muscle
reconstructions leave out this muscle altogether or place the muscles in a
position that will not work.  This tail based muscle would have many
advantages.  The weight of the muscle would not need to be rotated with
every step, allowing faster rotating limbs than would an equivalently
muscled leg.  In addition, long muscle fibers would allow a good
mechanical advantage over a longer rotating distance than hip based
muscles.   Look how far the forth trochanter is from the hip socket to see
the mechanical advantage allowed. With people and birds as our bipedal
models, it is easy to see why this muscle would be overlooked.
   The best I can see, a tendon attaching to the forth trochanter would
extend past the hip based leg muscle before muscle fibers were attached
along a long tendon.  The location of the tendon should be visibal when
looking at the tail.
   The dinosaurs with short, downturned tails such as triceratops
probably were not as dependent on this muscle as were earlier dinosaurs.
                
Mark Shelly     Mark Shelly