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Re: SICB Report, part 1 (long)



see if anybody else can follow this thought...

Theropods stuck out in front and had long tails behind their center of
gravity above the legs-the basic T-shape

Birds don't stick out behind at all but MANY still stick out in
front-including the early forms we DO know.
What balances birds in this? the upright S-shaped posture of the neck
over the shoulder and keel

Wings are present in the early bird forms we do know but flight was not
universal, so I can suggest that the ability of flight is not why birds
could lose their tails without tipping over.  I suggest there was more
going on at the hips and in upper torso posture.  Birds don't have the
mess of ribs pressing almost into the pubis as dinosaurs did, for
example.

Perhaps the hands and arms had a function for a theropod that kept the
whole front end DOWN in the T-shape, but this function is NOT present in
birds, and this arms-down function MUST HAVE BEEN reduced in
protobirds.  If T rex had less functional use of it's reduced arms, WHY
did T rex still have the T-shaped posture?  What kept the T-shape?  Or
in other words, what do birds have (other than wings) that T rex lacked
so they could be upright?  

The spine would have to change in the area of the shoulder girdle so the
vertebrae would allow a more upright posture for one thing.  Weight of
the skeleton would have to shift away from the T-shape to a bent S-shape
(and in doing so the tail could be lost gradually without affecting
balance).  

This suggests that uprightness (S-shape) was present BEFORE the tail was
lost.  Was it?

-Betty Cunningham

luisrey wrote:
> Dinobirds shortened the tail little by little (I suspect as they got better
> at the flying business,the trunk also automatically adapted to that)