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Re:Archaeopteryx or Velociraptor



Re:Archaeopteryx or Velociraptors

>>   With the primary locomotion means being flight in this ancestral
>> group, the need for tail based Caudi-femoralis running muscles
>> would have been reduced, possibly resulting in the rear facing pubic
>> bones (for balance) and thinner, stiffer tails.

Thomas R. Holtz, Jr. replied
>There are other  biomechanical explanations for this reorganization of
>the pelvic/hindlimb/tail muscle complex, which may have been exapted into
>the flight tail of birds.

   If the pubic boot on theropods was used as a resting surface for a
theropod, rearward reversion could: a) allow a more vertical resting
position; b) allow a lower stalking position on ground; c) allow the
theropods to get closer to branches in climbing.
   If the pubic boot served as attachment point for muscles attached to
the top of the femur to both control rotation about the axis of the femur
and to prevent splaying of the femur, a rearward evolution might mean: a)
that other hip/femur muscles would have to perform some of this; b) that
some of these boot based muscles would be used to keep both femurs
retracted during flight (in place of the Caudi-femoralis muscles) so that
the tail angle and rotation could be controlled by hip based tail muscles
without interference; c) that these dinosaurs walked with a more upright
gait (seems improbable).
   The development of the ?drumstick muscles? for flexing the ankle and
driving the dinosaur forward may also have allowed for the forward
propulsion of the dinosaurs without much rotation of the femur.  This
might also allows forward motion without the need for the caudi-femoralis
muscle.  This would also explain why an ostrich has a short femur and
rotates it very little (compare Greg Paul,s diagrams p. 115 of Predatory
Dinosaurs).
  The rear ilium muscles from my dissections of chicken legs appear better
suited for rotating the knee joint or allowing retraction of a flexed knee
joint than for retracting the femur, although I?m sure it helps do this
also. However, birds (or dinosaurs) that have long iliums probably
developed this condition to help retract the femur.  Regardless, the short
length of this muscle (compared to the caudi-femoralis) probably resulted
in; a) shorter femurs in birds (or descendants of flying dinosaurs); b)
shorter rotation angles of the femur; c) retracting the femur primarily
when running at full speed.
   In summary, it would appear that a rear facing pubis and development of
 the ?drumstick? muscles may also have allowed the reduction (possibly for
weight reduction) of the caudi-femoralis.  Theropods with rear facing
pubes, relatively shorter femurs, and thinner tails may have had flying
ancestors.
    These are the only other biomechanical reasons I could come up with,
are there others that I am missing?
        Mark Shelly     Mark Shelly