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Re: Rex Fall part 2



Wayne Anderson wrote:

> Since the fibula seems far less important for load- bearing than the
> (unbroken) tibia, I can see that she may not have fallen, but I also
> think it's still likely that she did -- from whatever broke the bone
> in the first place.

      Why is that?  What do you think might have broken the bone?  

>         Broken tibias come in because the tibia is the main
> load-bearing bone in the lower leg, and a broken tibia would almost
> certainly involve a fall.  I was wondering if there are any healed
> broken tibias in captivity, which would be almost proof of surviving a
> fall.

     That was the point I inferred from Darren Tankes posting that there 
were healed fibulas, but no known breaks in the femur or tibia that 
showed any signs of healing, implying that the animal died when its leg 
broke or not too long after.  And again, the important theme is death OR 
serious damage.  Evn if the fall isn't fatal, the impact is potentially 
crippling.  Not good.    
 
>         As far as the speed the Rex was traveling when he/she
> hypothetically falls, I don't see that it makes much
> difference. 

     The idea is that the faster an animal is moving, the more likely it 
is to trip, and the more difficult it would be to recover from the trip 
before it fell.

>         The vertical component of the fall is what causes the 6g
> impact on the torso, and 14g on the head -- if we accept Farlow's
> figures unmodified.

      Farlow included models discussing the speed and skid component of 
the fall, which I haven't got around to posting yet.

> 
>         By the way, wouldn't a simple "drop" fall result in the torso
> weight landing directly on the pubis? 

     Yes, but if it was moving forward at the time, it wouldn't just drop 
straight down, due to inertia.  The pubis would probably hit the ground, 
but so would the front part of the body.

>         1) The pubis, acting as a vertical load-bearing column, is
> able to withstand the impact (highly questionable), transferring it to
> the rest of the pelvis.  The pelvis being attached to the vertebrae
> can absorb most of the shock in vertebral flexion -- that is, the
> dino's body would bend.
 
     If the pubis, a somewhat hefty bone, is going to break from the 
impact (wich I agree it probably would) imagine the damage the same force 
could to to the animal's back.  Dinosaur dorsal vertebrae have a fair 
amount of lateral flexibility, but not much vertical flexibility. 

>         3) A lack of any such evidence might be taken as indicating
> that PERHAPS the dinos took some form of rolling action, probably
> sideward, to avoid direct falls.

    From dropping straight down?  In any case, no on has 
anwswered my challange that the ribs and scalulae would be as ill 
suited to sustain the impact forces as any other bones.  Remember 
that the relationship between bone strength and mass is not 
linear.  Finally, the lack of impact broken bones may only 
indicate that T.rexs were by and large being careful to avoid falling, which 
is what I've been arguing.            
 
LN Jeff
O-
p.s.: I got to hear Jane Goodal talk last night.